Note the following details of the code protection feature on Microchip devices:
•Microchip products meet the specification contained in their particular Microchip Data Sheet.
•Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the
intended manner and under normal conditions.
•There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our
knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data
Sheets. Most likely, the person doing so is engaged in theft of intellectual property.
•Microchip is willing to work with the customer who is concerned about the integrity of their code.
•Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not
mean that we are guaranteeing the product as “unbreakable.”
Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our
products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts
allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.
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The Microchip name and logo, the Microchip logo, Accuron,
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Microchip received ISO/TS-16949:2002 certification for its worldwide
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Company’s quality system processes and procedures are for its PIC
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6.0Flash Program Memory.............................................................................................................................................................. 95
8.08 x 8 Hardware Multiplier..........................................................................................................................................................111
17.0 Master Synchronous Serial Port (MSSP) Module ....................................................................................................................187
21.0 Comparator Voltage Reference Module...................................................................................................................................263
24.0 Special Features of the CPU.................................................................................................................................................... 343
25.0 Instruction Set Summary..........................................................................................................................................................361
26.0 Development Support............................................................................................................................................................... 411
28.0 DC and AC Characteristics Graphs and Tables.......................................................................................................................451
Appendix D: Migration From Baseline to Enhanced Devices............................................................................................................. 462
Appendix E: Migration from Mid-Range to Enhanced Devices .......................................................................................................... 463
Appendix F: Migration from High-End to Enhanced Devices............................................................................................................. 463
Index ..................................................................................................................................................................................................465
The Microchip Web Site..................................................................................................................................................................... 477
Customer Change Notification Service ..............................................................................................................................................477
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This document contains device specific information for
the following devices:
• PIC18F2585
• PIC18F2680
• PIC18F4585
• PIC18F4680
This family of devices offers the advantages of all PIC18
microcontrollers – namely, high computational
performance at an economical price – with the addition
of high-endurance, Enhanced Flash program memory.
In addition to these features, the
PIC18F2585/2680/4585/4680 family introduces design
enhancements that make these microcontrollers a
logical choice for many high-performance, power
sensitive applications.
1.1New Core Features
1.1.1nanoWatt TECHNOLOGY
All of the devices in the PIC18F2585/2680/4585/4680
family incorporate a range of features that can significantly reduce power consumption during operation.
Key items include:
• Alternate Run Modes: By clocking the controller
from the Timer1 source or the internal oscillator
block, power consumption during code execution
can be reduced by as much as 90%.
• Multiple Idle Modes: The controller can also run
with its CPU core disabled but the peripherals still
active. In these states, power consumption can be
reduced even further, to as little as 4% of normal
operation requirements.
• On-the-fly Mode Switching: The power
managed modes are invoked by user code during
operation, allowing the user to incorporate
power-saving ideas into their application’s
software design.
• Lower Consumption in Key Modules: The
power requirements for both Timer1 and the
Watchdog Timer have been reduced by up to
80%, with typical values of 1.1 and 2.1 μA,
respectively.
• Extended Instruction Set: In addition to the
standard 75 instructions of the PIC18 instruction
set, PIC18F2585/2680/4585/4680 devices also
provide an optional extension to the core CPU
functionality. The added features include eight
additional instructions that augment indirect and
indexed addressing operations and the
implementation of Indexed Literal Offset
Addressing mode for many of the standard PIC18
instructions.
1.1.2MULTIPLE OSCILLATOR OPTIONS
AND FEATURES
All of the devices in the PIC18F2585/2680/4585/4680
family offer ten different oscillator options, allowing
users a wide range of choices in developing application
hardware. These include:
• Four Crystal modes, using crystals or ceramic
resonators
• Two External Clock modes, offering the option of
using two pins (oscillator input and a divide-by-4
clock output) or one pin (oscillator input, with the
second pin reassigned as general I/O)
• Two External RC Oscillator modes with the same
pin options as the External Clock modes
• An internal oscillator block which provides an
8 MHz clock (±2% accuracy) and an INTRC
source (approximately 31 kHz, stable over
temperature and V
6 user selectable clock frequencies, between
125 kHz to 4 MHz, for a total of 8 clock
frequencies. This option frees the two oscillator
pins for use as additional general purpose I/O.
• A Phase Lock Loop (PLL) frequency multiplier,
available to both the high-speed crystal and
internal oscillator modes, which allows clock
speeds of up to 40 MHz. Used with the internal
oscillator, the PLL gives users a complete
selection of clock speeds, from 31 kHz to
32 MHz – all without using an external crystal or
clock circuit.
Besides its availability as a clock source, the internal
oscillator block provides a stable reference source that
gives the family additional features for robust
operation:
• Fail-Safe Clock Monitor: This option constantly
monitors the main clock source against a reference signal provided by the internal oscillator. If a
clock failure occurs, the controller is switched to
the internal oscillator block, allowing for continued
low-speed operation or a safe application
shutdown.
• Two-Speed Start-up: This option allows the
internal oscillator to serve as the clock source
from Power-on Reset, or wake-up from Sleep
mode, until the primary clock source is available.
• Memory Endurance: The Enhanced Flash cells
for both program memory and data EEPROM are
rated to last for many thousands of erase/write
cycles – up to 100,000 for program memory and
1,000,000 for EEPROM. Data retention without
refresh is conservatively estimated to be greater
than 40 years.
• Self-programmability: These devices can write
to their own program memory spaces under internal software control. By using a bootloader routine located in the protected Boot Block at the top
of program memory, it becomes possible to create
an application that can update itself in the field.
• Extended Instruction Set: The
PIC18F2585/2680/4585/4680 family introduces
an optional extension to the PIC18 instruction set,
which adds 8 new instructions and an Indexed
Addressing mode. This extension, enabled as a
device configuration option, has been specifically
designed to optimize re-entrant application code
originally developed in high-level languages, such
as C.
• Enhanced CCP1 module: In PWM mode, this
module provides 1, 2 or 4 modulated outputs for
controlling half-bridge and full-bridge drivers.
Other features include Auto-Shutdown, for
disabling PWM outputs on interrupt or other select
conditions and Auto-Restart, to reactivate outputs
once the condition has cleared.
• Enhanced Addressable USART: This serial
communication module is capable of standard
RS-232 operation and provides support for the LIN
bus protocol. Other enhancements include
automatic baud rate detection and a 16-bit Baud
Rate Generator for improved resolution. When the
microcontroller is using the internal oscillator
block, the EUSART provides stable operation for
applications that talk to the outside world without
using an external crystal (or its accompanying
power requirement).
• 10-bit A/D Converter: This module incorporates
programmable acquisition time, allowing for a
channel to be selected and a conversion to be
initiated without waiting for a sampling period and
thus, reduce code overhead.
• Extended Watchdog Timer (WDT): This
enhanced version incorporates a 16-bit prescaler,
allowing a time-out range from 4 ms to over
131 seconds, that is stable across operating
voltage and temperature.
1.3Details on Individual Family
Members
Devices in the PIC18F2585/2680/4585/4680 family are
available in 28-pin (PIC18F2X8X) and 40/44-pin
(PIC18F4X8X) packages. Block diagrams for the two
groups are shown in Figure 1-1 and Figure 1-2.
The devices are differentiated from each other in six
ways:
1.Flash program memory (48 Kbytes for
PIC18FX585 devices, 64 Kbytes for
PIC18FX680).
2.A/D channels (8 for PIC18F2X8X devices, 11 for
PIC18F4X8X devices).
3.I/O ports (3 bidirectional ports and 1 input only
port on PIC18F2X8X devices, 5 bidirectional
ports on PIC18F4X8X devices).
4.CCP1 and Enhanced CCP1 implementation
(PIC18F2X8X devices have 1 standard CCP1
module, PIC18F4X8X devices have one
standard CCP1 module and one ECCP1
module).
5.Parallel Slave Port (present only on
PIC18F4X8X devices).
6.PIC18F4X8X devices provide two comparators.
All other features for devices in this family are identical.
These are summarized in Table 1-1.
The pinouts for all devices are listed in Table 1-2 and
Table 1-3.
Like all Microchip PIC18 devices, members of the
PIC18F2585/2680/4585/4680 family are available as
both standard and low-voltage devices. Standard
devices with Enhanced Flash memory, designated with
an “F” in the part number (such as PIC18F2585),
accommodate an operating V
Low-voltage parts, designated by “LF” (such as
PIC18LF2585), function over an extended V
of 2.0V to 5.5V.
ST = Schmitt Trigger input with CMOS levels I= Input
O= Output P= Power
Number
PDIP,
SOIC
10
Pin
Buffer
Type
1
9
P
I/O
O
O
I/O
Type
Master Clear (input) or programming voltage (input).
I
ST
I
ST
I
ST
I
CMOS
TTL
—
—
TTL
Master Clear (Reset) input. This pin is an active-low
Reset to the device.
Programming voltage input.
Digital input.
Oscillator crystal or external clock input.
Oscillator crystal input or external clock source input.
ST buffer when configured in RC mode; CMOS otherwise.
External clock source input. Always associated with pin
function OSC1. (See related OSC1/CLKI, OSC2/CLKO pins.)
General purpose I/O pin.
Oscillator crystal or clock output.
Oscillator crystal output. Connects to crystal or resonator in
Crystal Oscillator mode.
In RC mode, OSC2 pin outputs CLKO which has 1/4 the
frequency of OSC1 and denotes the instruction cycle rate.
General purpose I/O pin.
ST = Schmitt Trigger input with CMOS levels I= Input
O= Output P= Power
Pin Number
PDIPQFNTQFP
11818
133230
143331
Pin
Typ e
I
P
I
I
I
I/O
O
O
I/O
Buffer
Type
ST
ST
ST
CMOS
TTL
—
—
TTL
Description
Master Clear (input) or programming voltage (input).
Master Clear (Reset) input. This pin is an
active-low Reset to the device.
Programming voltage input.
Digital input.
Oscillator crystal or external clock input.
Oscillator crystal input or external clock source input.
ST buffer when configured in RC mode;
CMOS otherwise.
External clock source input. Always associated with
pin function OSC1. (See related OSC1/CLKI,
OSC2/CLKO pins.)
General purpose I/O pin.
Oscillator crystal or clock output.
Oscillator crystal output. Connects to crystal or
resonator in Crystal Oscillator mode.
In RC mode, OSC2 pin outputs CLKO which has 1/4
the frequency of OSC1 and denotes the instruction
cycle rate.
General purpose I/O pin.
ST = Schmitt Trigger input with CMOS levels I= Input
O= Output P= Power
Pin Number
PDIPQFNTQFP
193838
203939
214040
224141
2722
2833
2944
3055
Pin
Typ e
I/O
I/O
I
I/O
I/O
I
I/O
I/O
I
I/O
I/O
I
I/O
I/O
I/O
O
I/O
I/O
O
I/O
I/O
O
I/O
I/O
O
Buffer
Type
ST
TTL
Analog
ST
TTL
Analog
ST
TTL
Analog
ST
TTL
Analog
ST
TTL
ST
TTL
ST
TTL
TTL
ST
TTL
TTL
ST
TTL
TTL
Description
PORTD is a bidirectional I/O port or a Parallel Slave
Port (PSP) for interfacing to a microprocessor port.
These pins have TTL input buffers when PSP module
is enabled.
Digital I/O.
Parallel Slave Port data.
Comparator 1 input (+).
Digital I/O.
Parallel Slave Port data.
Comparator 1 input (-)
Digital I/O.
Parallel Slave Port data.
Comparator 2 input (+).
Digital I/O.
Parallel Slave Port data.
Comparator 2 input (-).
Digital I/O.
Parallel Slave Port data.
Capture2 input/Compare2 output/PWM2 output.
ECCP1 PWM output A.
Digital I/O.
Parallel Slave Port data.
ECCP1 PWM output B.
Digital I/O.
Parallel Slave Port data.
ECCP1 PWM output C.
Digital I/O.
Parallel Slave Port data.
ECCP1 PWM output D.
PIC18F2585/2680/4585/4680 devices can be operated
in ten different oscillator modes. The user can program
the Configuration bits, FOSC3:FOSC0, in Configuration
Register 1H to select one of these ten modes:
1.LPLow-Power Crystal
2.XTCrystal/Resonator
3.HSHigh-Speed Crystal/Resonator
4.HSPLL High-Speed Crystal/Resonator
with PLL enabled
5.RCExternal Resistor/Capacitor with
F
OSC/4 output on RA6
6.RCIOExternal Resistor/Capacitor with I/O
on RA6
7.INTIO1 Internal Oscillator with F
on RA6 and I/O on RA7
8.INTIO2 Internal Oscillator with I/O on RA6
and RA7
9.ECExternal Clock with F
10. ECIOExternal Clock with I/O on RA6
2.2Crystal Oscillator/Ceramic
Resonators
In XT, LP, HS or HSPLL Oscillator modes, a crystal or
ceramic resonator is connected to the OSC1 and
OSC2 pins to establish oscillation. Figure 2-1 shows
the pin connections.
The oscillator design requires the use of a parallel cut
crystal.
Note:Use of a series cut crystal may give a
frequency out of the crystal manufacturer’s
specifications.
OSC/4 output
OSC/4 output
FIGURE 2-1:CRYSTAL/CERAMIC
RESONATOR OPERATION
(XT, LP, HS OR HSPLL
CONFIGURATION)
(1)
C1
(1)
C2
Note 1: See Table 2-1 and Table 2-2 for initial values of
2: A series resistor (R
3: R
OSC1
XTAL
OSC2
C1 and C2.
strip cut crystals.
F varies with the oscillator mode chosen.
(3)
RF
Sleep
PIC18FXXXX
S) may be required for AT
To
Logic
TABLE 2-1:CAPACITOR SELECTION FOR
CERAMIC RESONATORS
Typical Capacitor Values Used:
ModeFreqOSC1OSC2
XT455 kHz
2.0 MHz
4.0 MHz
HS8.0 MHz
16.0 MHz
Capacitor values are for design guidance only.
These capacitors were tested with the resonators
listed below for basic start-up and operation. Thesevalues are not optimized.
Different capacitor values may be required to produce
acceptable oscillator operation. The user should test
the performance of the oscillator over the expected
DD and temperature range for the application.
V
See the notes on page 24 for additional information.
Resonators Used:
56 pF
47 pF
33 pF
27 pF
22 pF
56 pF
47 pF
33 pF
27 pF
22 pF
455 kHz4.0 MHz
2.0 MHz8.0 MHz
16.0 MHz
Note:When using resonators with frequencies
above 3.5 MHz, the use of HS mode,
rather than XT mode, is recommended.
HS mode may be used at any V
DD for
which the controller is rated. If HS is
selected, it is possible that the gain of the
oscillator will overdrive the resonator.
Therefore, a series resistor should be
placed between the OSC2 pin and the
resonator. As a good starting point, the
recommended value of R
Capacitor values are for design guidance only.
These capacitors were tested with the crystals listed
below for basic start-up and operation. These values
are not optimized.
Different capacitor values may be required to produce
acceptable oscillator operation. The user should test
the performance of the oscillator over the expected
DD and temperature range for the application.
V
See the notes following this table for additional
information.
Note 1: Higher capacitance increases the stability
Crystal
Freq
200 kHz15 pF15 pF
4 MHz27 pF27 pF
8 MHz22 pF22 pF
20 MHz15 pF15 pF
Crystals Used:
32 kHz4 MHz
200 kHz8 MHz
1 MHz20 MHz
of the oscillator but also increases the
start-up time.
2: When operating below 3V V
using certain ceramic resonators at any
voltage, it may be necessary to use the
HS mode or switch to a crystal oscillator.
3: Since each resonator/crystal has its own
characteristics, the user should consult
the resonator/crystal manufacturer for
appropriate values of external
components.
4: Rs may be required to avoid overdriving
crystals with low drive level specification.
5: Always verify oscillator performance over
DD and temperature range that is
the V
expected for the application.
Typical Capacitor Values
Tested:
C1C2
DD, or when
An external clock source may also be connected to the
OSC1 pin in the HS mode, as shown in Figure 2-2.
FIGURE 2-2:EXTERNAL CLOCK
INPUT OPERATION
(HS OSCILLATOR
CONFIGURATION)
Clock from
Ext. System
Open
OSC1
OSC2
PIC18FXXXX
(HS Mode)
2.3External Clock Input
The EC and ECIO Oscillator modes require an external
clock source to be connected to the OSC1 pin. There is
no oscillator start-up time required after a Power-on
Reset or after an exit from Sleep mode.
In the EC Oscillator mode, the oscillator frequency
divided by 4 is available on the OSC2 pin. This signal
may be used for test purposes or to synchronize other
logic. Figure 2-3 shows the pin connections for the EC
Oscillator mode.
FIGURE 2-3:EXTERNAL CLOCK
INPUT OPERATION
(EC CONFIGURATION)
Clock from
Ext. System
F
OSC/4
The ECIO Oscillator mode functions like the EC mode,
except that the OSC2 pin becomes an additional
general purpose I/O pin. The I/O pin becomes bit 6 of
PORTA (RA6). Figure 2-4 shows the pin connections
for the ECIO Oscillator mode.
For timing insensitive applications, the “RC” and
“RCIO” device options offer additional cost savings.
The actual oscillator frequency is a function of several
factors:
• supply voltage
• values of the external resistor (R
capacitor (C
EXT)
• operating temperature
Given the same device, operating voltage and temperature and component values, there will also be unit-to-unit
frequency variations. These are due to factors such as:
• normal manufacturing variation
• difference in lead frame capacitance between
package types (especially for low C
• variations within the tolerance of limits of R
EXT
and C
In the RC Oscillator mode, the oscillator frequency
divided by 4 is available on the OSC2 pin. This signal
may be used for test purposes or to synchronize other
logic. Figure 2-5 shows how the R/C combination is
connected.
FIGURE 2-5:RC OSCILLATOR MODE
VDD
REXT
OSC1
CEXT
VSS
F
Recommended values: 3 kΩ ≤ REXT ≤ 100 kΩ
OSC/4
OSC2/CLKO
EXT > 20 pF
C
EXT) and
EXT values)
EXT
Internal
Clock
PIC18FXXXX
2.5PLL Frequency Multiplier
A Phase Locked Loop (PLL) circuit is provided as an
option for users who wish to use a lower frequency
oscillator circuit or to clock the device up to its highest
rated frequency from a crystal oscillator. This may be
useful for customers who are concerned with EMI due
to high-frequency crystals or users who require higher
clock speeds from an internal oscillator.
2.5.1HSPLL OSCILLATOR MODE
The HSPLL mode makes use of the HS mode oscillator
for frequencies up to 10 MHz. A PLL then multiplies the
oscillator output frequency by 4 to produce an internal
clock frequency up to 40 MHz.
The PLL is only available to the crystal oscillator when
the FOSC3:FOSC0 Configuration bits are programmed
for HSPLL mode (= 0110).
FIGURE 2-7:PLL BLOCK DIAGRAM
(HS MODE)
HS Osc Enable
PLL Enable
(from Configuration Register 1H)
OSC2
OSC1
HS Mode
Crystal
Osc
IN
F
FOUT
÷4
Phase
Comparator
Loop
Filter
VCO
SYSCLK
MUX
The RCIO Oscillator mode (Figure 2-6) functions like
the RC mode, except that the OSC2 pin becomes an
additional general purpose I/O pin. The I/O pin
becomes bit 6 of PORTA (RA6).
2.5.2PLL AND INTOSC
The PLL is also available to the internal oscillator block
in selected oscillator modes. In this configuration, the
FIGURE 2-6:RCIO OSCILLATOR MODE
VDD
PLL is enabled in software and generates a clock
output of up to 32MHz. The operation of INTOSC with
the PLL is described in Section 2.6.4 “PLL in INTOSC
The PIC18F2585/2680/4585/4680 devices include an
internal oscillator block which generates two different
clock signals; either can be used as the microcontroller’s
clock source. This may eliminate the need for external
oscillator circuits on the OSC1 and/or OSC2 pins.
The main output (INTOSC) is an 8MHz clock source,
which can be used to directly drive the device clock. It
also drives a postscaler, which can provide a range of
clock frequencies from 31 kHz to 4 MHz. The INTOSC
output is enabled when a clock frequency from 125 kHz
to 8 MHz is selected.
The other clock source is the internal RC oscillator
(INTRC), which provides a nominal 31 kHz output.
INTRC is enabled if it is selected as the device clock
source; it is also enabled automatically when any of the
following are enabled:
• Power-up Timer
• Fail-Safe Clock Monitor
• Watchdog Timer
• Two-Speed Start-up
These features are discussed in greater detail in
Section 24.0 “Special Features of the CPU”.
The clock source frequency (INTOSC direct, INTRC
direct or INTOSC postscaler) is selected by configuring
the IRCF bits of the OSCCON register (Register 2-2).
bit 6PLLEN: Frequency Multiplier PLL for INTOSC Enable bit
1 = PLL enabled for INTOSC (4 MHz and 8 MHz only)
0 = PLL disabled
Note 1: Available only in certain oscillator configurations; otherwise, this bit is unavailable
bit 5Unimplemented: Read as ‘0’
bit 4-0TUN4:TUN0: Frequency Tuning bits
01111 = Maximum frequency
• •
• •
00001
00000 = Center frequency. Oscillator module is running at the calibrated frequency.
11111
• •
• •
10000 = Minimum frequency
(1)
(1)
and reads as ‘0’. See text for details.
U-0R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
—TUN4TUN3TUN2TUN1TUN0
(1)
Legend:
R = Readable bitW = Writable bitU = Unimplemented bit, read as ‘0’
-n = Value at POR‘1’ = Bit is set‘0’ = Bit is clearedx = Bit is unknown
2.6.5.1Compensating with the EUSART
An adjustment may be required when the EUSART
begins to generate framing errors or receives data with
errors while in Asynchronous mode. Framing errors
indicate that the device clock frequency is too high. To
adjust for this, decrement the value in OSCTUNE to
reduce the clock frequency. On the other hand, errors
in data may suggest that the clock speed is too low. To
compensate, increment OSCTUNE to increase the
clock frequency.
2.6.5.2Compensating with the Timers
This technique compares device clock speed to some
reference clock. Two timers may be used; one timer is
clocked by the peripheral clock, while the other is
clocked by a fixed reference source, such as the
Timer1 oscillator.
Both timers are cleared, but the timer clocked by the
reference generates interrupts. When an interrupt
occurs, the internally clocked timer is read and both
timers are cleared. If the internally clocked timer value
is greater than expected, then the internal oscillator
block is running too fast. To adjust for this, decrement
the OSCTUNE register.
2.6.5.3Compensating with the CCP1
Module in Capture Mode
The CCP1 module can use free running Timer1 (or
Timer3), clocked by the internal oscillator block and an
external event with a known period (i.e., AC power
frequency). The time of the first event is captured in the
CCPRxH:CCPRxL registers and is recorded for use
later. When the second event causes a capture, the
time of the first event is subtracted from the time of the
second event. Since the period of the external event is
known, the time difference between events can be
calculated.
If the measured time is much greater than the
calculated time, the internal oscillator block is running
too fast. To compensate, decrement the OSCTUNE
register. If the measured time is much less than the
calculated time, the internal oscillator block is running
too slow. To compensate, increment the OSCTUNE
register.
Like previous PIC18 devices, the PIC2585/2680/
4585/4680 family includes a feature that allows the
device clock source to be switched from the main
oscillator to an alternate low-frequency clock source.
PIC18F2585/2680/4585/4680 devices offer two alternate clock sources. When an alternate clock source is
enabled, the various power managed operating modes
are available.
Essentially, there are three clock sources for these
devices:
• Primary oscillators
• Secondary oscillators
• Internal oscillator block
The primary oscillators include the External Crystal
and Resonator modes, the External RC modes, the
External Clock modes and the internal oscillator block.
The particular mode is defined by the FOSC3:FOSC0
Configuration bits. The details of these modes are
covered earlier in this chapter.
The secondary oscillators are those external sources
not connected to the OSC1 or OSC2 pins. These
sources may continue to operate even after the
controller is placed in a power managed mode.
PIC18F2585/2680/4585/4680 devices offer the Timer1
oscillator as a secondary oscillator. This oscillator, in all
power managed modes, is often the time base for
functions such as a real-time clock.
Most often, a 32.768kHz watch crystal is connected
between the RC0/T1OSO/T13CKI and RC1/T1OSI
pins. Like the LP mode oscillator circuit, loading
capacitors are also connected from each pin to ground.
The Timer1 oscillator is discussed in greater detail in
Section 12.3 “Timer1 Oscillator”.
In addition to being a primary clock source, the internaloscillator block is available as a power managed
mode clock source. The INTRC source is also used as
the clock source for several special features, such as
the WDT and Fail-Safe Clock Monitor.
The clock sources for the PIC18F2585/2680/4585/4680
devices are shown in Figure 2-8. See Section 24.0“Special Features of the CPU” for Configuration
The OSCCON register (Register 2-2) controls several
aspects of the device clock’s operation, both in full
power operation and in power managed modes.
The System Clock Select bits, SCS1:SCS0, select the
clock source. The available clock sources are the
primary clock (defined by the FOSC3:FOSC0 Configuration bits), the secondary clock (Timer1 oscillator) and
the internal oscillator block. The clock source changes
immediately after one or more of the bits is written to,
following a brief clock transition interval. The SCS bits
are cleared on all forms of Reset.
The Internal Oscillator Frequency Select bits,
IRCF2:IRCF0, select the frequency output of the
internal oscillator block to drive the device clock. The
choices are the INTRC source, the INTOSC source
(8 MHz) or one of the frequencies derived from the
INTOSC postscaler (31kHz to 4 MHz). If the internal
oscillator block is supplying the device clock, changing
the states of these bits will have an immediate change
on the internal oscillator’s output. On device Resets,
the default output frequency of the internal oscillator
block is set at 1 MHz.
When an output frequency of 31 kHz is selected
(IRCF2:IRCF0 = 000), users may choose which
internal oscillator acts as the source. This is done with
the INTSRC bit in the OSCTUNE register
(OSCTUNE<7>). Setting this bit selects INTOSC as a
31.25 kHz clock source by enabling the divide-by-256
output of the INTOSC postscaler. Clearing INTSRC
selects INTRC (nominally 31 kHz) as the clock source.
This option allows users to select the tunable and more
precise INTOSC as a clock source, while maintaining
power savings with a very low clock speed. Regardless
of the setting of INTSRC, INTRC always remains the
clock source for features such as the Watchdog Timer
and the Fail-Safe Clock Monitor.
The OSTS, IOFS and T1RUN bits indicate which clock
source is currently providing the device clock. The
OSTS bit indicates that the Oscillator Start-up Timer
has timed out and the primary clock is providing the
device clock in primary clock modes. The IOFS bit
indicates when the internal oscillator block has
stabilized and is providing the device clock in RC Clock
modes. The T1RUN bit (T1CON<6>) indicates when
the Timer1 oscillator is providing the device clock in
secondary clock modes. In power managed modes,
only one of these three bits will be set at any time. If
none of these bits are set, the INTRC is providing the
clock or the internal oscillator block has just started and
is not yet stable.
The IDLEN bit determines if the device goes into Sleep
mode or one of the Idle modes when the SLEEP
instruction is executed.
The use of the flag and control bits in the OSCCON
register is discussed in more detail in Section 3.0
“Power Managed Modes”.
Note 1: The Timer1 oscillator must be enabled to
select the secondary clock source. The
Timer1 oscillator is enabled by setting the
T1OSCEN bit in the Timer1 Control register (T1CON<3>). If the Timer1 oscillator is
not enabled, then any attempt to select a
secondary clock source when executing a
SLEEP instruction will be ignored.
2: It is recommended that the Timer1
oscillator be operating and stable before
executing the SLEEP instruction, or a very
long delay may occur while the Timer1
oscillator starts.
2.7.2OSCILLATOR TRANSITIONS
PIC18F2585/2680/4585/4680 devices contain circuitry
to prevent clock “glitches” when switching between
clock sources. A short pause in the device clock occurs
during the clock switch. The length of this pause is the
sum of two cycles of the old clock source and three to
four cycles of the new clock source. This formula
assumes that the new clock source is stable.
Clock transitions are discussed in greater detail in
Section 3.1.2 “Entering Power Managed Modes”.
2.8Effects of Power Managed Modes
on the Various Clock Sources
When PRI_IDLE mode is selected, the designated
primary oscillator continues to run without interruption.
For all other power managed modes, the oscillator
using the OSC1 pin is disabled. The OSC1 pin (and
OSC2 pin, if used by the oscillator) will stop oscillating.
In secondary clock modes (SEC_RUN and
SEC_IDLE), the Timer1 oscillator is operating and
providing the device clock. The Timer1 oscillator may
also run in all power managed modes if required to
clock Timer1 or Timer3.
In internal oscillator modes (RC_RUN and RC_IDLE),
the internal oscillator block provides the device clock
source. The 31 kHz INTRC output can be used directly
to provide the clock and may be enabled to support
various special features, regardless of the power
managed mode (see Section 24.2 “Watchdog Timer
(WDT)”, Section 24.3 “Two-Speed Start-up” and
Section 24.4 “Fail-Safe Clock Monitor” for more
information on WDT, Two-Speed Start-up and Fail-Safe
Clock Monitor). The INTOSC output at 8 MHz may be
used directly to clock the device or may be divided
down by the postscaler. The INTOSC output is disabled
if the clock is provided directly from the INTRC output.
If the Sleep mode is selected, all clock sources are
stopped. Since all the transistor switching currents
have been stopped, Sleep mode achieves the lowest
current consumption of the device (only leakage
currents).
Enabling any on-chip feature that will operate during
Sleep will increase the current consumed during Sleep.
The INTRC is required to support WDT operation. The
Timer1 oscillator may be operating to support a
real-time clock. Other features may be operating that
do not require a device clock source (i.e., SSP slave,
PSP, INTn pins and others). Peripherals that may add
significant current consumption are listed in
Section 27.2 “DC Characteristics: Power Down and
Supply Current”.
2.9Power-up Delays
Power-up delays are controlled by two timers, so that
no external Reset circuitry is required for most applications. The delays ensure that the device is kept in
Reset until the device power supply is stable under normal circumstances and the primary clock is operating
and stable. For additional information on power-up
delays, see Section 4.5 “Device Reset Timers”.
The first timer is the Power-up Timer (PWRT), which
provides a fixed delay on power-up (parameter 33,
Table 27-10). It is enabled by clearing (= 0) the
PWRTEN
The second timer is the Oscillator Start-up Timer
(OST), intended to keep the chip in Reset until the
crystal oscillator is stable (LP, XT and HS modes). The
OST does this by counting 1024 oscillator cycles
before allowing the oscillator to clock the device.
When the HSPLL Oscillator mode is selected, the
device is kept in Reset for an additional 2 ms, following
the HS mode OST delay, so the PLL can lock to the
incoming clock frequency.
There is a delay of interval T
Table 27-10), following POR, while the controller
becomes ready to execute instructions. This delay runs
concurrently with any other delays. This may be the
only delay that occurs when any of the EC, RC or INTIO
modes are used as the primary clock source.
Configuration bit.
CSD (parameter 38,
TABLE 2-3:OSC1 AND OSC2 PIN STATES IN SLEEP MODE
OSC ModeOSC1 PinOSC2 Pin
RC, INTIO1Floating, external resistor should pull highAt logic low (clock/4 output)
RCIO, INTIO2Floating, external resistor should pull highConfigured as PORTA, bit 6
ECIOFloating, pulled by external clockConfigured as PORTA, bit 6
ECFloating, pulled by external clockAt logic low (clock/4 output)
LP, XT and HSFeedback inverter disabled at quiescent
voltage level
Note:See Table 4-2 in Section 4.0 “Reset” for time-outs due to Sleep and MCLR
PIC18F2585/2680/4585/4680 devices offer a total of
seven operating modes for more efficient power
management. These modes provide a variety of
options for selective power conservation in applications
where resources may be limited (i.e., battery-powered
devices).
There are three categories of power managed modes:
• Run modes
• Idle modes
• Sleep mode
These categories define which portions of the device
are clocked and sometimes, what speed. The Run and
Idle modes may use any of the three available clock
sources (primary, secondary or internal oscillator
block); the Sleep mode does not use a clock source.
The power managed modes include several power
saving features offered on previous PIC
is the clock switching feature, offered in other PIC18
devices, allowing the controller to use the Timer1
oscillator in place of the primary oscillator. Also
included is the Sleep mode, offered by all PIC devices,
where all device clocks are stopped.
3.1Selecting Power Managed Modes
Selecting a power managed mode requires two
decisions: if the CPU is to be clocked or not and the
selection of a clock source. The IDLEN bit
(OSCCON<7>) controls CPU clocking, while the
SCS1:SCS0 bits (OSCCON<1:0>) select the clock
source. The individual modes, bit settings, clock sources
and affected modules are summarized in Table 3-1.
®
devices. One
3.1.1CLOCK SOURCES
The SCS1:SCS0 bits allow the selection of one of three
clock sources for power managed modes. They are:
• the primary clock, as defined by the
FOSC3:FOSC0 Configuration bits
• the secondary clock (the Timer1 oscillator)
• the internal oscillator block (for RC modes)
3.1.2ENTERING POWER MANAGED
MODES
Switching from one power managed mode to another
begins by loading the OSCCON register. The
SCS1:SCS0 bits select the clock source and determine
which Run or Idle mode is to be used. Changing these
bits causes an immediate switch to the new clock
source, assuming that it is running. The switch may
also be subject to clock transition delays. These are
discussed in Section 3.1.3 “Clock Transitions AndStatus Indicators” and subsequent sections.
Entry to the Power Managed Idle or Sleep modes is
triggered by the execution of a SLEEP instruction. The
actual mode that results depends on the status of the
IDLEN bit.
Depending on the current mode and the mode being
switched to, a change to a power managed mode does
not always require setting all of these bits. Many
transitions may be done by changing the oscillator
select bits, or changing the IDLEN bit, prior to issuing a
SLEEP instruction. If the IDLEN bit is already
configured correctly, it may only be necessary to
perform a SLEEP instruction to switch to the desired
mode.
TABLE 3-1:POWER MANAGED MODES
Mode
IDLEN<7>
Sleep0N/AOffOffNone – All clocks are disabled
PRI_RUNN/A00ClockedClockedPrimary – LP, XT, HS, HSPLL, RC, EC, INTRC
The length of the transition between clock sources is
the sum of two cycles of the old clock source and three
to four cycles of the new clock source. This formula
assumes that the new clock source is stable.
Three bits indicate the current clock source and its
status. They are:
• OSTS (OSCCON<3>)
• IOFS (OSCCON<2>)
• T1RUN (T1CON<6>)
In general, only one of these bits will be set while in a
given power managed mode. When the OSTS bit is
set, the primary clock is providing the device clock.
When the IOFS bit is set, the INTOSC output is providing a stable 8MHz clock source to a divider that
actually drives the device clock. When the T1RUN bit is
set, the Timer1 oscillator is providing the clock. If none
of these bits are set, then either the INTRC clock
source is clocking the device, or the INTOSC source is
not yet stable.
If the internal oscillator block is configured as the
primary clock source by the FOSC3:FOSC0 Configuration bits, then both the OSTS and IOFS bits may be set
when in PRI_RUN or PRI_IDLE modes. This indicates
that the primary clock (INTOSC output) is generating a
stable 8 MHz output. Entering another RC power
managed mode at the same frequency would clear the
OSTS bit.
Note 1: Caution should be used when modifying a
single IRCF bit. If V
possible to select a higher clock speed
than is supported by the low VDD.
Improper device operation may result if
the VDD/FOSC specifications are violated.
2: Executing a SLEEP instruction does not
necessarily place the device into Sleep
mode. It acts as the trigger to place the
controller into either the Sleep mode or
one of the Idle modes, depending on the
setting of the IDLEN bit.
DD is less than 3V, it is
3.1.4MULTIPLE SLEEP COMMANDS
The power managed mode that is invoked with the
SLEEP instruction is determined by the setting of the
IDLEN bit at the time the instruction is executed. If
another SLEEP instruction is executed, the device will
enter the power managed mode specified by IDLEN at
that time. If IDLEN has changed, the device will enter
the new power managed mode specified by the new
setting.
3.2Run Modes
In the Run modes, clocks to both the core and
peripherals are active. The difference between these
modes is the clock source.
3.2.1PRI_RUN MODE
The PRI_RUN mode is the normal, full power execution
mode of the microcontroller. This is also the default
mode upon a device Reset, unless Two-Speed Start-up
is enabled (see Section 24.3 “Two-Speed Start-up”
for details). In this mode, the OSTS bit is set. The IOFS
bit may be set if the internal oscillator block is the
primary clock source (see Section 2.7.1 “OscillatorControl Register”).
3.2.2SEC_RUN MODE
The SEC_RUN mode is the compatible mode to the
“clock switching” feature offered in other PIC18
devices. In this mode, the CPU and peripherals are
clocked from the Timer1 oscillator. This gives users the
option of lower power consumption while still using a
high accuracy clock source.
SEC_RUN mode is entered by setting the SCS1:SCS0
bits to ‘01’. The device clock source is switched to the
Timer1 oscillator (see Figure 3-1), the primary oscillator is shut down, the T1RUN bit (T1CON<6>) is set and
the OSTS bit is cleared.
Note:The Timer1 oscillator should already be
running prior to entering SEC_RUN mode.
If the T1OSCEN bit is not set when the
SCS1:SCS0 bits are set to ‘01’, entry to
SEC_RUN mode will not occur. If the
Timer1 oscillator is enabled but not yet
running, device clocks will be delayed until
the oscillator has started. In such situations, initial oscillator operation is far from
stable and unpredictable operation may
result.
On transitions from SEC_RUN mode to PRI_RUN, the
peripherals and CPU continue to be clocked from the
Timer1 oscillator while the primary clock is started.
When the primary clock becomes ready, a clock switch
back to the primary clock occurs (see Figure 3-2).
When the clock switch is complete, the T1RUN bit is
cleared, the OSTS bit is set and the primary clock is
providing the clock. The IDLEN and SCS bits are not
affected by the wake-up; the Timer1 oscillator
continues to run.
FIGURE 3-1:TRANSITION TIMING FOR ENTRY TO SEC_RUN MODE
FIGURE 3-2:TRANSITION TIMING FROM SEC_RUN MODE TO PRI_RUN MODE (HSPLL)
3.2.3RC_RUN MODE
In RC_RUN mode, the CPU and peripherals are
clocked from the internal oscillator block using the
INTOSC multiplexer; the primary clock is shut down.
When using the INTRC source, this mode provides the
best power conservation of all the Run modes, while
still executing code. It works well for user applications
which are not highly timing sensitive or do not require
high-speed clocks at all times.
If the primary clock source is the internal oscillator
block (either INTRC or INTOSC), there are no distinguishable differences between PRI_RUN and
RC_RUN modes during execution. However, a clock
switch delay will occur during entry to and exit from
RC_RUN mode. Therefore, if the primary clock source
is the internal oscillator block, the use of RC_RUN
mode is not recommended.
This mode is entered by setting SCS1 to ‘1’. Although
it is ignored, it is recommended that SCS0 also be
cleared; this is to maintain software compatibility with
future devices. When the clock source is switched to
the INTOSC multiplexer (see Figure3-3), the primary
oscillator is shut down and the OSTS bit is cleared. The
IRCF bits may be modified at any time to immediately
PIC18F2585/2680/4585/4680
If the IRCF bits and the INTSRC bit are all clear, the
INTOSC output is not enabled and the IOFS bit will
remain clear; there will be no indication of the current
clock source. The INTRC source is providing the
device clocks.
If the IRCF bits are changed from all clear (thus,
enabling the INTOSC output) or if INTSRC is set, the
IOFS bit becomes set after the INTOSC output
becomes stable. Clocks to the device continue while
the INTOSC source stabilizes after an interval of
IOBST.
T
On transitions from RC_RUN mode to PRI_RUN mode,
the device continues to be clocked from the INTOSC
multiplexer while the primary clock is started. When the
primary clock becomes ready, a clock switch to the
primary clock occurs (see Figure 3-4). When the clock
switch is complete, the IOFS bit is cleared, the OSTS
bit is set and the primary clock is providing the device
clock. The IDLEN and SCS bits are not affected by the
switch. The INTRC source will continue to run if either
the WDT or the Fail-Safe Clock Monitor is enabled.
If the IRCF bits were previously at a non-zero value or
if INTSRC was set before setting SCS1 and the
INTOSC source was already stable, the IOFS bit will
remain set.
FIGURE 3-3:TRANSITION TIMING TO RC_RUN MODE
Q4Q3Q2
Q1
123n-1n
Clock Transition
PC + 2PC
INTRC
OSC1
CPU
Clock
Peripheral
Clock
Program
Counter
Q1
Q4Q3Q2Q1Q3Q2
PC + 4
FIGURE 3-4:TRANSITION TIMING FROM RC_RUN MODE TO PRI_RUN MODE
Q3 Q4
Q1
Q1
INTOSC
Multiplexer
OSC1
PLL Clock
Output
CPU Clock
Peripheral
Clock
Program
Counter
SCS1:SCS0 bits changed
Note 1: TOST = 1024 TOSC; TPLL = 2 ms (approx). These intervals are not shown to scale.
The Power Managed Sleep mode in the
PIC18F2585/2680/4585/4680 devices is identical to
the legacy Sleep mode offered in all other PIC devices.
It is entered by clearing the IDLEN bit (the default state
on device Reset) and executing the SLEEP instruction.
This shuts down the selected oscillator (Figure 3-5). All
clock source status bits are cleared.
Entering the Sleep mode from any other mode does not
require a clock switch. This is because no clocks are
needed once the controller has entered Sleep. If the
WDT is selected, the INTRC source will continue to
operate. If the Timer1 oscillator is enabled, it will also
continue to run.
When a wake event occurs in Sleep mode (by interrupt,
Reset or WDT time-out), the device will not be clocked
until the clock source selected by the SCS1:SCS0 bits
becomes ready (see Figure 3-6), or it will be clocked
from the internal oscillator block if either the
Two-Speed Start-up or the Fail-Safe Clock Monitor are
enabled (see Section 24.0 “Special Features of theCPU”). In either case, the OSTS bit is set when the
primary clock is providing the device clocks. The
IDLEN and SCS bits are not affected by the wake-up.
3.4Idle Modes
The Idle modes allow the controller’s CPU to be
selectively shut down while the peripherals continue to
operate. Selecting a particular Idle mode allows users
to further manage power consumption.
If the IDLEN bit is set to a ‘1’ when a SLEEP instruction is
executed, the peripherals will be clocked from the clock
source selected using the SCS1:SCS0 bits; however, the
CPU will not be clocked. The clock source status bits are
not affected. Setting IDLEN and executing a SLEEP
instruction provides a quick method of switching from a
given Run mode to its corresponding Idle mode.
If the WDT is selected, the INTRC source will continue
to operate. If the Timer1 oscillator is enabled, it will also
continue to run.
Since the CPU is not executing instructions, the only
exits from any of the Idle modes are by interrupt, WDT
time-out or a Reset. When a wake event occurs, CPU
execution is delayed by an interval of T
(parameter 38, Table 27-10) while it becomes ready to
execute code. When the CPU begins executing code,
it resumes with the same clock source for the current
Idle mode. For example, when waking from RC_IDLE
mode, the internal oscillator block will clock the CPU
and peripherals (in other words, RC_RUN mode). The
IDLEN and SCS bits are not affected by the wake-up.
While in any Idle mode or the Sleep mode, a WDT
time-out will result in a WDT wake-up to the Run mode
currently specified by the SCS1:SCS0 bits.
CSD
FIGURE 3-5:TRANSITION TIMING FOR ENTRY TO SLEEP MODE
Q4Q3Q2
Q1Q1
OSC1
CPU
Clock
Peripheral
Clock
Sleep
Program
Counter
PC + 2PC
FIGURE 3-6:TRANSITION TIMING FOR WAKE FROM SLEEP (HSPLL)
OSC1
PLL Clock
Output
CPU Clock
Peripheral
Clock
Program
Counter
Note1: T
Q1Q2 Q3 Q4 Q1 Q2
(1)
TOST
Wake Event
OST = 1024 TOSC; TPLL = 2 ms (approx). These intervals are not shown to scale.
This mode is unique among the three Low-Power Idle
modes, in that it does not disable the primary device
clock. For timing sensitive applications, this allows for
the fastest resumption of device operation with its more
accurate primary clock source, since the clock source
does not have to “warm up” or transition from another
oscillator.
PRI_IDLE mode is entered from PRI_RUN mode by
setting the IDLEN bit and executing a SLEEP instruction. If the device is in another Run mode, set IDLEN
first, then clear the SCS bits and execute SLEEP.
Although the CPU is disabled, the peripherals continue
to be clocked from the primary clock source specified
by the FOSC3:FOSC0 Configuration bits. The OSTS
bit remains set (see Figure3-7).
When a wake event occurs, the CPU is clocked from the
primary clock source. A delay of interval T
required between the wake event and when code
execution starts. This is required to allow the CPU to
become ready to execute instructions. After the
wake-up, the OSTS bit remains set. The IDLEN and
SCS bits are not affected by the wake-up (see
Figure 3-8).
CSD is
3.4.2SEC_IDLE MODE
In SEC_IDLE mode, the CPU is disabled but the
peripherals continue to be clocked from the Timer1
oscillator. This mode is entered from SEC_RUN by setting the IDLEN bit and executing a SLEEP instruction. If
the device is in another Run mode, set the IDLEN bit
first, then set the SCS1:SCS0 bits to ‘01’ and execute
SLEEP. When the clock source is switched to the
Timer1 oscillator, the primary oscillator is shut down,
the OSTS bit is cleared and the T1RUN bit is set.
When a wake event occurs, the peripherals continue to
be clocked from the Timer1 oscillator. After an interval of
CSD following the wake event, the CPU begins
T
executing code being clocked by the Timer1 oscillator.
The IDLEN and SCS bits are not affected by the
wake-up; the Timer1 oscillator continues to run (see
Figure 3-8).
Note:The Timer1 oscillator should already be
running prior to entering SEC_IDLE mode.
If the T1OSCEN bit is not set when the
SLEEP instruction is executed, the SLEEP
instruction will be ignored and entry to
SEC_IDLE mode will not occur. If the
Timer1 oscillator is enabled but not yet running, peripheral clocks will be delayed until
the oscillator has started. In such situations,
initial oscillator operation is far from stable
and unpredictable operation may result.
FIGURE 3-7:TRANSITION TIMING FOR ENTRY TO IDLE MODE
Q1
OSC1
CPU Clock
Peripheral
Clock
Program
Counter
Q1
Q2
Q3
PCPC + 2
Q4
FIGURE 3-8:TRANSITION TIMING FOR WAKE FROM IDLE TO RUN MODE
In RC_IDLE mode, the CPU is disabled but the peripherals continue to be clocked from the internal oscillator
block using the INTOSC multiplexer. This mode allows
for controllable power conservation during Idle periods.
From RC_RUN, this mode is entered by setting the
IDLEN bit and executing a SLEEP instruction. If the
device is in another Run mode, first set IDLEN, then set
the SCS1 bit and execute SLEEP. Although its value is
ignored, it is recommended that SCS0 also be cleared;
this is to maintain software compatibility with future
devices. The INTOSC multiplexer may be used to
select a higher clock frequency, by modifying the IRCF
bits, before executing the SLEEP instruction. When the
clock source is switched to the INTOSC multiplexer, the
primary oscillator is shut down and the OSTS bit is
cleared.
If the IRCF bits are set to any non-zero value or the
INTSRC bit is set, the INTOSC output is enabled. The
IOFS bit becomes set, after the INTOSC output
becomes stable, after an interval of T
(parameter 39, Table 27-10). Clocks to the peripherals
continue while the INTOSC source stabilizes. If the
IRCF bits were previously at a non-zero value, or
INTSRC was set before the SLEEP instruction was
executed and the INTOSC source was already stable,
the IOFS bit will remain set. If the IRCF bits and
INTSRC are all clear, the INTOSC output will not be
enabled, the IOFS bit will remain clear and there will be
no indication of the current clock source.
When a wake event occurs, the peripherals continue to
be clocked from the INTOSC multiplexer. After a delay
CSD following the wake event, the CPU begins
of T
executing code being clocked by the INTOSC multiplexer. The IDLEN and SCS bits are not affected by the
wake-up. The INTRC source will continue to run if
either the WDT or the Fail-Safe Clock Monitor is
enabled.
IOBST
3.5Exiting Idle and Sleep Modes
An exit from Sleep mode or any of the Idle modes is
triggered by an interrupt, a Reset or a WDT time-out.
This section discusses the triggers that cause exits
from power managed modes. The clocking subsystem
actions are discussed in each of the power managed
modes (see Section 3.2 “Run Modes”, Section 3.3“Sleep Mode” and Section 3.4 “Idle Modes”).
3.5.1EXIT BY INTERRUPT
Any of the available interrupt sources can cause the
device to exit from an Idle mode or the Sleep mode to
a Run mode. To enable this functionality, an interrupt
source must be enabled by setting its enable bit in one
of the INTCON or PIE registers. The exit sequence is
initiated when the corresponding interrupt flag bit is set.
On all exits from Idle or Sleep modes by interrupt, code
execution branches to the interrupt vector if the
GIE/GIEH bit (INTCON<7>) is set. Otherwise, code
execution continues or resumes without branching
(see Section 9.0 “Interrupts”).
A fixed delay of interval T
is required when leaving Sleep and Idle modes. This
delay is required for the CPU to prepare for execution.
Instruction execution resumes on the first clock cycle
following this delay.
CSD following the wake event
3.5.2EXIT BY WDT TIME-OUT
A WDT time-out will cause different actions depending
on which power managed mode the device is in when
the time-out occurs.
If the device is not executing code (all Idle modes and
Sleep mode), the time-out will result in an exit from the
power managed mode (see Section 3.2 “Run Modes”
and Section 3.3 “Sleep Mode”). If the device is
executing code (all Run modes), the time-out will result
in a WDT Reset (see Section 24.2 “Watchdog Timer(WDT)”).
The WDT timer and postscaler are cleared by executing a SLEEP or CLRWDT instruction, the loss of a
currently selected clock source (if the Fail-Safe Clock
Monitor is enabled) and modifying the IRCF bits in the
OSCCON register if the internal oscillator block is the
device clock source.
3.5.3EXIT BY RESET
Normally, the device is held in Reset by the Oscillator
Start-up Timer (OST) until the primary clock becomes
ready. At that time, the OSTS bit is set and the device
begins executing code. If the internal oscillator block is
the new clock source, the IOFS bit is set instead.
The exit delay time from Reset to the start of code
execution depends on both the clock sources before
and after the wake-up and the type of oscillator if the
new clock source is the primary clock. Exit delays are
summarized in Table 3-2.
Code execution can begin before the primary clock
becomes ready. If either the Two-Speed Start-up (see
Section 24.3 “Two-Speed Start-up”) or Fail-Safe
Clock Monitor (see Section 24.4 “Fail-Safe ClockMonitor”) is enabled, the device may begin execution
as soon as the Reset source has cleared. Execution is
clocked by the INTOSC multiplexer driven by the
internal oscillator block. Execution is clocked by the
internal oscillator block until either the primary clock
becomes ready or a power managed mode is entered
before the primary clock becomes ready; the primary
clock is then shut down.
Certain exits from power managed modes do not
invoke the OST at all. There are two cases:
• PRI_IDLE mode where the primary clock source
is not stopped; and
• the primary clock source is not any of the LP, XT,
HS or HSPLL modes.
In these instances, the primary clock source either
does not require an oscillator start-up delay, since it is
already running (PRI_IDLE), or normally does not
require an oscillator start-up delay (RC, EC and INTIO
Oscillator modes). However, a fixed delay of interval
CSD following the wake event is still required when
T
leaving Sleep and Idle modes to allow the CPU to prepare for execution. Instruction execution resumes on
the first clock cycle following this delay.
TABLE 3-2:EXIT DELAY ON WAKE-UP BY RESET FROM SLEEP MODE OR ANY IDLE MODE
(BY CLOCK SOURCES)
Clock Source
Before Wake-up
Primary Device Clock
(PRI_IDLE mode)
T1OSC or INTRC
INTOSC
None
(Sleep mode)
Note 1:In this instance, refers specifically to the 31 kHz INTRC clock source.
2:TCSD (parameter 38) is a required delay when waking from Sleep and all Idle modes and runs concurrently
with any other required delays (see Section 3.4 “Idle Modes”).
3:Includes both the INTOSC 8 MHz source and postscaler derived frequencies.
4:T
OST is the Oscillator Start-up Timer (parameter 32). t
also designated as T
5:Execution continues during T
(1)
(3)
PLL.
Clock Source
After Wake-up
Exit Delay
LP, XT, HS
(2)
EC, RC
(1)
INTRC
INTOSC
(3)
LP, XT, HSTOST
EC, RC
(1)
INTRC
INTOSC
(2)
LP, XT, HSTOST
EC, RC
(1)
INTRC
INTOSC
(2)
LP, XT, HST
EC, RC
(1)
INTRC
INTOSC
IOBST (parameter 39), the INTOSC stabilization period.
This section discusses Resets generated by MCLR
POR and BOR and covers the operation of the various
start-up timers. Stack Reset events are covered in
Section 5.1.2.4 “Stack Full and Underflow Resets”.
WDT Resets are covered in Section 24.2 “Watchdog
,
4.1RCON Register
Device Reset events are tracked through the RCON
register (Register 4-1). The lower five bits of the
register indicate that a specific Reset event has
occurred. In most cases, these bits can only be cleared
by the event and must be set by the application after
the event. The state of these flag bits, taken together,
can be read to indicate the type of Reset that just
occurred. This is described in more detail in
Section 4.6 “Reset State of Registers”.
The RCON register also has control bits for setting
interrupt priority (IPEN) and software control of the
BOR (SBOREN). Interrupt priority is discussed in
Section 9.0 “Interrupts”. BOR is covered in
Section 4.4 “Brown-out Reset (BOR)”.
Timer (WDT)”.
FIGURE 4-1:SIMPLIFIED BLOCK DIAGRAM OF ON-CHIP RESET CIRCUIT
RESET
Instruction
Stack
Pointer
Stack Full/Underflow Reset
MCLR
VDD
OSC1
( )_IDLE
Sleep
WDT
Time-out
DD Rise
V
Detect
Brown-out
Reset
OST/PWRT
32 μs
(1)
INTRC
External Reset
MCLRE
POR Pulse
BOREN
OST
PWRT
1024 Cycles
10-bit Ripple Counter
65.5 ms
11-bit Ripple Counter
S
Chip_Reset
R
Q
Enable PWRT
Enable OST
(2)
Note 1: This is the INTRC source from the internal oscillator block and is separate from the RC oscillator of the CLKI pin.
was set to ‘1’ by software immediately after POR).
is ‘0’ and POR is ‘1’ (assuming
PIC18F2585/2680/4585/4680
4.2Master Clear Reset (MCLR)
The MCLR pin provides a method for triggering an
external Reset of the device. A Reset is generated by
holding the pin low. These devices have a noise filter in
the MCLR
pulses.
The MCLR
including the WDT.
In PIC18F2585/2680/4585/4680 devices, the MCLR
input can be disabled with the MCLRE Configuration
bit. When MCLR
input. See Section 10.5 “PORTE, TRISE and LATE
PIC18F2585/2680/4585/4680 devices implement a BOR
circuit that provides the user with a number of configuration and power-saving options. The BOR is controlled by
the BORV1:BORV0 and BOREN1:BOREN0 Configuration bits. There are a total of four BOR configurations
which are summarized in Table 4-1.
The BOR threshold is set by the BORV1:BORV0 bits. If
BOR is enabled (any values of BOREN1:BOREN0,
except ‘00’), any drop of V
D005) for greater than T
the device. A Reset may or may not occur if V
below V
Brown-out Reset until V
If the Power-up Timer is enabled, it will be invoked after
V
Reset for an additional time delay, T
(parameter 33). If VDD drops below VBOR while the
Power-up Timer is running, the chip will go back into a
Brown-out Reset and the Power-up Timer will be
initialized. Once V
Timer will execute the additional time delay.
BOR and the Power-on Timer (PWRT) are
independently configured. Enabling BOR Reset does
not automatically enable the PWRT.
BOR for less than TBOR. The chip will remain in
DD rises above VBOR; it then will keep the chip in
DD rises above VBOR, the Power-up
4.4.1SOFTWARE ENABLED BOR
When BOREN1:BOREN0 = 01, the BOR can be
enabled or disabled by the user in software. This is
done with the control bit, SBOREN (RCON<6>).
Setting SBOREN enables the BOR to function as
previously described. Clearing SBOREN disables the
BOR entirely. The SBOREN bit operates only in this
mode; otherwise it is read as ‘0’.
DD below VBOR (parameter
BOR (parameter 35) will reset
DD falls
DD rises above VBOR.
PWRT
Placing the BOR under software control gives the user
the additional flexibility of tailoring the application to its
environment without having to reprogram the device to
change BOR configuration. It also allows the user to
tailor device power consumption in software by eliminating the incremental current that the BOR consumes.
While the BOR current is typically very small, it may
have some impact in low-power applications.
Note:Even when BOR is under software control,
the BOR Reset voltage level is still set by
the BORV1:BORV0 Configuration bits. It
cannot be changed in software.
4.4.2DETECTING BOR
When BOR is enabled, the BOR bit always resets to ‘0’
on any BOR or POR event. This makes it difficult to
determine if a BOR event has occurred just by reading
the state of BOR
simultaneously check the state of both POR
This assumes that the POR
immediately after any POR event. IF BOR
POR
is ‘1’, it can be reliably assumed that a BOR event
has occurred.
alone. A more reliable method is to
and BOR.
bit is reset to ‘1’ in software
is ‘0’ while
4.4.3DISABLING BOR IN SLEEP MODE
When BOREN1:BOREN0 = 10, the BOR remains
under hardware control and operates as previously
described. Whenever the device enters Sleep mode,
however, the BOR is automatically disabled. When the
device returns to any other operating mode, BOR is
automatically re-enabled.
This mode allows for applications to recover from
brown-out situations, while actively executing code,
when the device requires BOR protection the most. At
the same time, it saves additional power in Sleep mode
by eliminating the small incremental BOR current.
TABLE 4-1:BOR CONFIGURATIONS
BOR Configuration Status of
BOREN1BOREN0
00UnavailableBOR disabled; must be enabled by reprogramming the Configuration bits.
01AvailableBOR enabled in software; operation controlled by SBOREN.
10UnavailableBOR enabled in hardware in Run and Idle modes, disabled during Sleep
11UnavailableBOR enabled in hardware; must be disabled by reprogramming the
PIC18F2585/2680/4585/4680 devices incorporate
three separate on-chip timers that help regulate the
Power-on Reset process. Their main function is to
ensure that the device clock is stable before code is
executed. These timers are:
• Power-up Timer (PWRT)
• Oscillator Start-up Timer (OST)
• PLL Lock Time-out
4.5.1POWER-UP TIMER (PWRT)
The Power-up Timer (PWRT) of PIC18F2585/2680/
4585/4680 devices is an 11-bit counter which uses the
INTRC source as the clock input. This yields an
approximate time interval of 2048 x 32 μs=65.6ms.
While the PWRT is counting, the device is held in
Reset.
The power-up time delay depends on the INTRC clock
and will vary from chip to chip due to temperature and
process variation. See DC parameter 33 for details.
The PWRT is enabled by clearing the PWRTEN
Configuration bit.
4.5.2OSCILLATOR START-UP TIMER
(OST)
The Oscillator Start-up Timer (OST) provides a 1024
oscillator cycle (from OSC1 input) delay after the
PWRT delay is over (parameter 33). This ensures that
the crystal oscillator or resonator has started and
stabilized.
The OST time-out is invoked only for XT, LP, HS and
HSPLL modes and only on Power-on Reset or on exit
from most power managed modes.
4.5.3PLL LOCK TIME-OUT
With the PLL enabled in its PLL mode, the time-out
sequence following a Power-on Reset is slightly
different from other oscillator modes. A separate timer
is used to provide a fixed time-out that is sufficient for
the PLL to lock to the main oscillator frequency. This
PLL lock time-out (T
the oscillator start-up time-out.
PLL) is typically 2 ms and follows
4.5.4TIME-OUT SEQUENCE
On power-up, the time-out sequence is as follows:
1.After the POR pulse has cleared, PWRT
time-out is invoked (if enabled).
2.Then, the OST is activated.
The total time-out will vary based on oscillator configuration and the status of the PWRT. Figure 4-3,
Figure 4-4, Figure 4-5, Figure 4-6 and Figure4-7 all
depict time-out sequences on power-up, with the
Power-up Timer enabled and the device operating in
HS Oscillator mode. Figures 4-3 through 4-6 also apply
to devices operating in XT or LP modes. For devices in
RC mode and with the PWRT disabled, on the other
hand, there will be no time-out at all.
Since the time-outs occur from the POR pulse, if MCLR
is kept low long enough, all time-outs will expire.
Bringing MCLR
(Figure 4-5). This is useful for testing purposes or to
synchronize more than one PIC18FXXXX device
operating in parallel.
high will begin execution immediately
TABLE 4-2:TIME-OUT IN VARIOUS SITUATIONS
Oscillator
Configuration
HSPLL66 ms
HS, XT, LP66 ms
EC, ECIO66 ms
RC, RCIO66 ms
INTIO1, INTIO266 ms
Note 1: 66 ms (65.5 ms) is the nominal Power-up Timer (PWRT) delay.
2:2 ms is the nominal time required for the PLL to lock.
Most registers are unaffected by a Reset. Their status
is unknown on POR and unchanged by all other
Table 4-4 describes the Reset states for all of the
Special Function Registers. These are categorized by
Power-on and Brown-out Resets, Master Clear and
WDT Resets and WDT wake-ups.
Resets. The other registers are forced to a “Reset
state” depending on the type of Reset that occurred.
Most registers are not affected by a WDT wake-up,
since this is viewed as the resumption of normal
operation. Status bits from the RCON register, RI
PD
, POR and BOR, are set or cleared differently in
, TO,
different Reset situations, as indicated in Table 4-3.
These bits are used in software to determine the nature
of the Reset.
TABLE 4-3:STATUS BITS, THEIR SIGNIFICANCE AND THE INITIALIZATION CONDITION FOR
Shaded cells indicate conditions do not apply for the designated device.
Note 1:One or more bits in the INTCONx or PIRx registers will be affected (to cause wake-up).
2:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the PC is loaded with the interrupt
vector (0008h or 0018h).
3:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the TOSU, TOSH and TOSL are
updated with the current value of the PC. The STKPTR is modified to point to the next location in the
hardware stack.
4:See Table 4-3 for Reset value for specific condition.
5:Bits 6 and 7 of PORTA, LATA and TRISA are enabled, depending on the oscillator mode selected. When
not enabled as PORTA pins, they are disabled and read ‘0’.
6:This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
Legend: u = unchanged, x = unknown, - = unimplemented bit, read as ‘0’, q = value depends on condition.
Note 1:One or more bits in the INTCONx or PIRx registers will be affected (to cause wake-up).
2:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the PC is loaded with the interrupt
3:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the TOSU, TOSH and TOSL are
4:See Table 4-3 for Reset value for specific condition.
5:Bits 6 and 7 of PORTA, LATA and TRISA are enabled, depending on the oscillator mode selected. When
6:This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
2585 2680 4585 46800q-1 11q00q-q qquuuq-u qquu
2680 4585 46800-00 00000-00 0000u-uu uuuu
Shaded cells indicate conditions do not apply for the designated device.
vector (0008h or 0018h).
updated with the current value of the PC. The STKPTR is modified to point to the next location in the
hardware stack.
not enabled as PORTA pins, they are disabled and read ‘0’.
Legend: u = unchanged, x = unknown, - = unimplemented bit, read as ‘0’, q = value depends on condition.
Note 1:One or more bits in the INTCONx or PIRx registers will be affected (to cause wake-up).
2:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the PC is loaded with the interrupt
3:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the TOSU, TOSH and TOSL are
4:See Table 4-3 for Reset value for specific condition.
5:Bits 6 and 7 of PORTA, LATA and TRISA are enabled, depending on the oscillator mode selected. When
6:This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
Shaded cells indicate conditions do not apply for the designated device.
Note 1:One or more bits in the INTCONx or PIRx registers will be affected (to cause wake-up).
2:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the PC is loaded with the interrupt
vector (0008h or 0018h).
3:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the TOSU, TOSH and TOSL are
updated with the current value of the PC. The STKPTR is modified to point to the next location in the
hardware stack.
4:See Table 4-3 for Reset value for specific condition.
5:Bits 6 and 7 of PORTA, LATA and TRISA are enabled, depending on the oscillator mode selected. When
not enabled as PORTA pins, they are disabled and read ‘0’.
6:This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
Shaded cells indicate conditions do not apply for the designated device.
Note 1:One or more bits in the INTCONx or PIRx registers will be affected (to cause wake-up).
2:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the PC is loaded with the interrupt
vector (0008h or 0018h).
3:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the TOSU, TOSH and TOSL are
updated with the current value of the PC. The STKPTR is modified to point to the next location in the
hardware stack.
4:See Table 4-3 for Reset value for specific condition.
5:Bits 6 and 7 of PORTA, LATA and TRISA are enabled, depending on the oscillator mode selected. When
not enabled as PORTA pins, they are disabled and read ‘0’.
6:This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
Shaded cells indicate conditions do not apply for the designated device.
Note 1:One or more bits in the INTCONx or PIRx registers will be affected (to cause wake-up).
2:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the PC is loaded with the interrupt
vector (0008h or 0018h).
3:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the TOSU, TOSH and TOSL are
updated with the current value of the PC. The STKPTR is modified to point to the next location in the
hardware stack.
4:See Table 4-3 for Reset value for specific condition.
5:Bits 6 and 7 of PORTA, LATA and TRISA are enabled, depending on the oscillator mode selected. When
not enabled as PORTA pins, they are disabled and read ‘0’.
6:This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
Shaded cells indicate conditions do not apply for the designated device.
Note 1:One or more bits in the INTCONx or PIRx registers will be affected (to cause wake-up).
2:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the PC is loaded with the interrupt
vector (0008h or 0018h).
3:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the TOSU, TOSH and TOSL are
updated with the current value of the PC. The STKPTR is modified to point to the next location in the
hardware stack.
4:See Table 4-3 for Reset value for specific condition.
5:Bits 6 and 7 of PORTA, LATA and TRISA are enabled, depending on the oscillator mode selected. When
not enabled as PORTA pins, they are disabled and read ‘0’.
6:This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
2585 2680 4585 4680xxxx xxxxuuuu uuuuuuuu uuuuLegend: u = unchanged, x = unknown, - = unimplemented bit, read as ‘0’, q = value depends on condition.
Shaded cells indicate conditions do not apply for the designated device.
Note 1:One or more bits in the INTCONx or PIRx registers will be affected (to cause wake-up).
2:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the PC is loaded with the interrupt
vector (0008h or 0018h).
3:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the TOSU, TOSH and TOSL are
updated with the current value of the PC. The STKPTR is modified to point to the next location in the
hardware stack.
4:See Table 4-3 for Reset value for specific condition.
5:Bits 6 and 7 of PORTA, LATA and TRISA are enabled, depending on the oscillator mode selected. When
not enabled as PORTA pins, they are disabled and read ‘0’.
6:This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
Legend: u = unchanged, x = unknown, - = unimplemented bit, read as ‘0’, q = value depends on condition.
Shaded cells indicate conditions do not apply for the designated device.
Note 1:One or more bits in the INTCONx or PIRx registers will be affected (to cause wake-up).
2:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the PC is loaded with the interrupt
vector (0008h or 0018h).
3:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the TOSU, TOSH and TOSL are
updated with the current value of the PC. The STKPTR is modified to point to the next location in the
hardware stack.
4:See Table 4-3 for Reset value for specific condition.
5:Bits 6 and 7 of PORTA, LATA and TRISA are enabled, depending on the oscillator mode selected. When
not enabled as PORTA pins, they are disabled and read ‘0’.
6:This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
Legend: u = unchanged, x = unknown, - = unimplemented bit, read as ‘0’, q = value depends on condition.
Shaded cells indicate conditions do not apply for the designated device.
Note 1:One or more bits in the INTCONx or PIRx registers will be affected (to cause wake-up).
2:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the PC is loaded with the interrupt
vector (0008h or 0018h).
3:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the TOSU, TOSH and TOSL are
updated with the current value of the PC. The STKPTR is modified to point to the next location in the
hardware stack.
4:See Table 4-3 for Reset value for specific condition.
5:Bits 6 and 7 of PORTA, LATA and TRISA are enabled, depending on the oscillator mode selected. When
not enabled as PORTA pins, they are disabled and read ‘0’.
6:This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
Legend: u = unchanged, x = unknown, - = unimplemented bit, read as ‘0’, q = value depends on condition.
Shaded cells indicate conditions do not apply for the designated device.
Note 1:One or more bits in the INTCONx or PIRx registers will be affected (to cause wake-up).
2:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the PC is loaded with the interrupt
vector (0008h or 0018h).
3:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the TOSU, TOSH and TOSL are
updated with the current value of the PC. The STKPTR is modified to point to the next location in the
hardware stack.
4:See Table 4-3 for Reset value for specific condition.
5:Bits 6 and 7 of PORTA, LATA and TRISA are enabled, depending on the oscillator mode selected. When
not enabled as PORTA pins, they are disabled and read ‘0’.
6:This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
Legend: u = unchanged, x = unknown, - = unimplemented bit, read as ‘0’, q = value depends on condition.
Shaded cells indicate conditions do not apply for the designated device.
Note 1:One or more bits in the INTCONx or PIRx registers will be affected (to cause wake-up).
2:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the PC is loaded with the interrupt
vector (0008h or 0018h).
3:When the wake-up is due to an interrupt and the GIEL or GIEH bit is set, the TOSU, TOSH and TOSL are
updated with the current value of the PC. The STKPTR is modified to point to the next location in the
hardware stack.
4:See Table 4-3 for Reset value for specific condition.
5:Bits 6 and 7 of PORTA, LATA and TRISA are enabled, depending on the oscillator mode selected. When
not enabled as PORTA pins, they are disabled and read ‘0’.
6:This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
There are three types of memory in PIC18 Enhanced
microcontroller devices:
• Program Memory
• Data RAM
• Data EEPROM
As Harvard architecture devices, the data and program
memories use separate busses; this allows for concurrent access of the two memory spaces. The data
EEPROM, for practical purposes, can be regarded as
a peripheral device, since it is addressed and accessed
through a set of control registers.
Additional detailed information on the operation of the
Flash program memory is provided in Section 6.0“Flash Program Memory”. Data EEPROM is
discussed separately in Section 7.0 “Data EEPROM
Memory”.
5.1Program Memory Organization
PIC18 microcontrollers implement a 21-bit program
counter, which is capable of addressing a 2-Mbyte
program memory space. Accessing a location between
the upper boundary of the physically implemented
memory and the 2-Mbyte address will return all ‘0’s (a
NOP instruction).
The PIC18F2585 and PIC18F4585 each have
48 Kbytes of Flash memory and can store up to 24,576
single-word instructions. The PIC18F2680 and
PIC18F4680 each have 64Kbytes of Flash memory
and can store up to 32,768 single-word instructions.
PIC18 devices have two interrupt vectors. The Reset
vector address is at 0000h and the interrupt vector
addresses are at 0008h and 0018h.
The program memory maps for PIC18FX585 and
PIC18FX680 devices are shown in Figure 5-1.
FIGURE 5-1:PROGRAM MEMORY MAP AND STACK FOR
PIC18F2585/2680/4585/4680 DEVICES
PIC18X585
PC<20:0>
CALL,RCALL,RETURN
RETFIE,RETLW
Stack Level 1
Stack Level 31
Reset Vector
High Priority Interrupt Vector
Low Priority Interrupt Vector
The Program Counter (PC) specifies the address of the
instruction to fetch for execution. The PC is 21 bits wide
and is contained in three separate 8-bit registers. The
low byte, known as the PCL register, is both readable
and writable. The high byte, or PCH register, contains
the PC<15:8> bits; it is not directly readable or writable.
Updates to the PCH register are performed through the
PCLATH register. The upper byte is called PCU. This
register contains the PC<20:16> bits; it is also not
directly readable or writable. Updates to the PCU
register are performed through the PCLATU register.
The contents of PCLATH and PCLATU are transferred
to the program counter by any operation that writes
PCL. Similarly, the upper two bytes of the program
counter are transferred to PCLATH and PCLATU by an
operation that reads PCL. This is useful for computed
offsets to the PC (see Section 5.1.4.1 “ComputedGOTO”).
The PC addresses bytes in the program memory. To
prevent the PC from becoming misaligned with word
instructions, the Least Significant bit of PCL is fixed to
a value of ‘0’. The PC increments by 2 to address
sequential instructions in the program memory.
The CALL, RCALL and GOTO program branch
instructions write to the program counter directly. For
these instructions, the contents of PCLATH and
PCLATU are not transferred to the program counter.
5.1.2RETURN ADDRESS STACK
The return address stack allows any combination of up
to 31 program calls and interrupts to occur. The PC is
pushed onto the stack when a CALL or RCALL instruction is executed or an interrupt is Acknowledged. The
PC value is pulled off the stack on a RETURN, RETLW
or a RETFIE instruction. PCLATU and PCLATH are not
affected by any of the RETURN or CALL instructions.
The stack operates as a 31-word by 21-bit RAM and a
5-bit Stack Pointer, STKPTR. The stack space is not
part of either program or data space. The Stack Pointer
is readable and writable and the address on the top of
the stack is readable and writable through the
top-of-stack Special File Registers. Data can also be
pushed to, or popped from the stack, using these
registers.
A CALL type instruction causes a push onto the stack;
the Stack Pointer is first incremented and the location
pointed to by the Stack Pointer is written with the
contents of the PC (already pointing to the instruction
following the CALL). A RETURN type instruction causes
a pop from the stack; the contents of the location
pointed to by the STKPTR are transferred to the PC
and then the Stack Pointer is decremented.
The Stack Pointer is initialized to ‘00000’ after all
Resets. There is no RAM associated with the location
corresponding to a Stack Pointer value of ‘00000’; this
is only a Reset value. Status bits indicate if the stack is
full or has overflowed or has underflowed.
5.1.2.1Top-of-Stack Access
Only the top of the return address stack (TOS) is
readable and writable. A set of three registers,
TOSU:TOSH:TOSL, hold the contents of the stack location pointed to by the STKPTR register (Figure 5-2). This
allows users to implement a software stack if necessary.
After a CALL, RCALL or interrupt, the software can read
the pushed value by reading the TOSU:TOSH:TOSL
registers. These values can be placed on a user defined
software stack. At return time, the software can return
these values to TOSU:TOSH:TOSL and do a return.
The user must disable the global interrupt enable bits
while accessing the stack to prevent inadvertent stack
corruption.
FIGURE 5-2:RETURN ADDRESS STACK AND ASSOCIATED REGISTERS
The STKPTR register (Register 5-1) contains the Stack
Pointer value, the STKFUL (Stack Full) status bit and
the STKUNF (Stack Underflow) status bits. The value
of the Stack Pointer can be 0 through 31. The Stack
Pointer increments before values are pushed onto the
stack and decrements after values are popped off the
stack. On Reset, the Stack Pointer value will be zero.
The user may read and write the Stack Pointer value.
This feature can be used by a Real-Time Operating
System (RTOS) for return stack maintenance.
After the PC is pushed onto the stack 31 times (without
popping any values off the stack), the STKFUL bit is
set. The STKFUL bit is cleared by software or by a
POR.
The action that takes place when the stack becomes
full depends on the state of the STVREN (Stack Overflow Reset Enable) Configuration bit. (Refer to
Section 24.1 “Configuration Bits” for a description of
the device Configuration bits.) If STVREN is set
(default), the 31st push will push the (PC + 2) value
onto the stack, set the STKFUL bit and reset the
device. The STKFUL bit will remain set and the Stack
Pointer will be set to zero.
If STVREN is cleared, the STKFUL bit will be set on the
31st push and the Stack Pointer will increment to 31.
Any additional pushes will not overwrite the 31st push
and STKPTR will remain at 31.
When the stack has been popped enough times to
unload the stack, the next pop will return a value of zero
to the PC and sets the STKUNF bit, while the Stack
Pointer remains at zero. The STKUNF bit will remain
set until cleared by software or until a POR occurs.
Note:Returning a value of zero to the PC on an
underflow has the effect of vectoring the
program to the Reset vector, where the
stack conditions can be verified and
appropriate actions can be taken. This is
not the same as a Reset, as the contents
of the SFRs are not affected.
5.1.2.3PUSH and POP Instructions
Since the Top-of-Stack is readable and writable, the
ability to push values onto the stack and pull values off
the stack without disturbing normal program execution
is a desirable feature. The PIC18 instruction set
includes two instructions, PUSH and POP, that permit
the TOS to be manipulated under software control.
TOSU, TOSH and TOSL can be modified to place data
or a return address on the stack.
The PUSH instruction places the current PC value onto
the stack. This increments the Stack Pointer and loads
the current PC value onto the stack.
The POP instruction discards the current TOS by decrementing the Stack Pointer. The previous value pushed
onto the stack then becomes the TOS value.
REGISTER 5-1:STKPTR: STACK POINTER REGISTER
R/C-0R/C-0U-0R/W-0R/W-0R/W-0R/W-0R/W-0
STKFUL
bit 7bit 0
bit 7STKFUL: Stack Full Flag bit
1 = Stack became full or overflowed
0 = Stack has not become full or overflowed
bit 6STKUNF: Stack Underflow Flag bit
1 = Stack underflow occurred
0 = Stack underflow did not occur
bit 5Unimplemented: Read as ‘0’
bit 4-0SP4:SP0: Stack Pointer Location bits
Legend:
R = Readable bitW = Writable bitU = UnimplementedC = Clearable only bit
-n = Value at POR‘1’ = Bit is set‘0’ = Bit is clearedx = Bit is unknown
(1)
STKUNF
Note 1: Bit 7 and bit 6 are cleared by user software or by a POR.
Device Resets on stack overflow and stack underflow
conditions are enabled by setting the STVREN bit in
Configuration Register 4L. When STVREN is set, a full
or underflow will set the appropriate STKFUL or
STKUNF bit and then cause a device Reset. When
STVREN is cleared, a full or underflow condition will set
the appropriate STKFUL or STKUNF bit, but not cause
a device Reset. The STKFUL or STKUNF bits are
cleared by the user software or a Power-on Reset.
5.1.3FAST REGISTER STACK
A fast register stack is provided for the STATUS,
WREG and BSR registers, to provide a “fast return”
option for interrupts. Each stack is only one level deep
and is neither readable nor writable. It is loaded with the
current value of the corresponding register when the
processor vectors for an interrupt. All interrupt sources
will push values into the stack registers. The values in
the registers are then loaded back into their associated
registers, if the RETFIE, FAST instruction is used to
return from the interrupt.
If both low and high priority interrupts are enabled, the
stack registers cannot be used reliably to return from
low priority interrupts. If a high priority interrupt occurs
while servicing a low priority interrupt, the stack register
values stored by the low priority interrupt will be
overwritten. In these cases, users must save the key
registers in software during a low priority interrupt.
If interrupt priority is not used, all interrupts may use the
fast register stack for returns from interrupt. If no interrupts are used, the fast register stack can be used to
restore the STATUS, WREG and BSR registers at the
end of a subroutine call. To use the fast register stack
for a subroutine call, a CALL label, FAST instruction
must be executed to save the STATUS, WREG and
BSR registers to the fast register stack. A
RETURN, FAST instruction is then executed to restore
these registers from the fast register stack.
Example 5-1 shows a source code example that uses
the fast register stack during a subroutine call and
return.
EXAMPLE 5-1:FAST REGISTER STACK
CODE EXAMPLE
CALL SUB1, FAST;STATUS, WREG, BSR
;SAVED IN FAST REGISTER
;STACK
•
•
SUB1 •
•
RETURN, FAST;RESTORE VALUES SAVED
;IN FAST REGISTER STACK
5.1.4LOOK-UP TABLES IN PROGRAM
MEMORY
There may be programming situations that require the
creation of data structures, or look-up tables, in
program memory. For PIC18 devices, look-up tables
can be implemented in two ways:
• Computed GOTO
• Table Reads
5.1.4.1Computed GOTO
A computed GOTO is accomplished by adding an offset
to the program counter. An example is shown in
Example 5-2.
A look-up table can be formed with an ADDWF PCL
instruction and a group of RETLW nn instructions. The
W register is loaded with an offset into the table before
executing a CALL to that table. The first instruction of
the called routine is the ADDWF PCL instruction. The
next instruction executed will be one of the RETLW nn
instructions, that returns the value ‘nn’ to the calling
function.
The offset value (in WREG) specifies the number of
bytes that the program counter should advance and
should be multiples of 2 (LSb = 0).
In this method, only one data byte may be stored in
each instruction location and room on the return
address stack is required.
EXAMPLE 5-2:COMPUTED GOTO USING
AN OFFSET VALUE
MOVFOFFSET, W
CALLTABLE
ORG nn00h
TABLEADDWFPCL
RETLWnnh
RETLWnnh
RETLWnnh
.
.
.
5.1.4.2Table Reads and Table Writes
A better method of storing data in program memory
allows two bytes of data to be stored in each instruction
location.
Look-up table data may be stored two bytes per
program word by using table reads and writes. The
Table Pointer (TBLPTR) register specifies the byte
address and the Table Latch (TABLAT) register
contains the data that is read from or written to program
memory. Data is transferred to or from program
memory one byte at a time.
Table read and table write operations are discussed
further in Section 6.1 “Table Reads and TableWrites”.
The microcontroller clock input, whether from an internal or external source, is internally divided by four to
generate four non-overlapping quadrature clocks (Q1,
Q2, Q3 and Q4). Internally, the Program Counter (PC)
is incremented on every Q1; the instruction is fetched
from the program memory and latched into the Instruction Register (IR) during Q4. The instruction is decoded
and executed during the following Q1 through Q4. The
clocks and instruction execution flow are shown in
Figure 5-3.
FIGURE 5-3:CLOCK/INSTRUCTION CYCLE
OSC1
Q1
Q2
Q3
Q4
PC
OSC2/CLKO
(RC mode)
Q2Q3Q4
Q1
PCPC + 2PC + 4
Execute INST (PC – 2)
Fetch INST (PC)
Q2Q3Q4
Q1
Execute INST (PC)
Fetch INST (PC + 2)
5.2.2INSTRUCTION FLOW/PIPELINING
An “Instruction Cycle” consists of four Q cycles: Q1
through Q4. The instruction fetch and execute are pipelined in such a manner that a fetch takes one instruction
cycle, while the decode and execute take another
instruction cycle. However, due to the pipelining, each
instruction effectively executes in one cycle. If an
instruction causes the program counter to change (e.g.,
GOTO), then two cycles are required to complete the
instruction (Example 5-3).
A fetch cycle begins with the program counter
incrementing in Q1.
In the execution cycle, the fetched instruction is latched
into the Instruction Register (IR) in cycle Q1. This
instruction is then decoded and executed during the
Q2, Q3 and Q4 cycles. Data memory is read during Q2
(operand read) and written during Q4 (destination
write).
Q2Q3Q4
Q1
Internal
Phase
Clock
Execute INST (PC + 2)
Fetch INST (PC + 4)
EXAMPLE 5-3:INSTRUCTION PIPELINE FLOW
TCY0TCY1TCY2TCY3TCY4TCY5
1. MOVLW 55h
2. MOVWF PORTB
3. BRA SUB_1
4. BSF PORTA, BIT3 (Forced NOP)
5. Instruction @ address SUB_1
Note:All instructions are single cycle, except for any program branches. These take two cycles since the
fetch instruction is “flushed” from the pipeline while the new instruction is being fetched and then
executed.
The program memory is addressed in bytes. Instructions are stored as two bytes or four bytes in program
memory. The Least Significant Byte of an instruction
word is always stored in a program memory location
with an even address (LSB = 0). To maintain alignment
with instruction boundaries, the PC increments in steps
of 2 and the LSB will always read ‘0’ (see Section 5.1.1“Program Counter”).
Figure 5-4 shows an example of how instruction words
are stored in the program memory.
The CALL and GOTO instructions have the absolute
program memory address embedded into the instruc-
tion. Since instructions are always stored on word
boundaries, the data contained in the instruction is a
word address. The word address is written to PC<20:1>,
which accesses the desired byte address in program
memory. Instruction #2 in Figure 5-4 shows how the
instruction GOTO 0006h is encoded in the program
memory. Program branch instructions, which encode a
relative address offset, operate in the same manner. The
offset value stored in a branch instruction represents the
number of single-word instructions that the PC will be
offset by. Section 25.0 “Instruction Set Summary”
provides further details of the instruction set.
The standard PIC18 instruction set has four two-word
instructions: CALL, MOVFF, GOTO and LSFR. In all
cases, the second word of the instructions always has
‘1111’ as its four Most Significant bits; the other 12 bits
are literal data, usually a data memory address.
The use of ‘1111’ in the 4 MSbs of an instruction
specifies a special form of NOP. If the instruction is
executed in proper sequence – immediately after the
first word – the data in the second word is accessed
and used by the instruction sequence. If the first word
is skipped for some reason and the second word is
executed by itself, a NOP is executed instead. This is
necessary for cases when the two-word instruction is
preceded by a conditional instruction that changes the
PC. Example 5-4 shows how this works.
Note:See Section 5.5 “Program Memory and
the Extended Instruction Set” for
information on two-word instructions in the
extended instruction set.
EXAMPLE 5-4:TWO-WORD INSTRUCTIONS
CASE 1:
Object CodeSource Code
0110 0110 0000 0000TSTFSZREG1; is RAM location 0?
1100 0001 0010 0011MOVFFREG1, REG2 ; No, skip this word
1111 0100 0101 0110; Execute this word as a NOP
0010 0100 0000 0000ADDWFREG3; continue code
CASE 2:
Object CodeSource Code
0110 0110 0000 0000TSTFSZREG1; is RAM location 0?
1100 0001 0010 0011MOVFFREG1, REG2 ; Yes, execute this word
memory are changed when the PIC18
extended instruction set is enabled. See
Section 5.6 “Data Memory and the
Extended Instruction Set” for more
information.
The data memory in PIC18 devices is implemented as
static RAM. Each register in the data memory has a
12-bit address, allowing up to 4096 bytes of data
memory. The memory space is divided into as many as
16 banks that contain 256 bytes each;
PIC18F2585/2680/4585/4680 devices implement all
16 banks. Figure 5-5 shows the data memory
organization for the PIC18F2585/2680/4585/4680
devices.
The data memory contains Special Function Registers
(SFRs) and General Purpose Registers (GPRs). The
SFRs are used for control and status of the controller
and peripheral functions, while GPRs are used for data
storage and scratchpad operations in the user’s
application. Any read of an unimplemented location will
read as ‘0’s.
The instruction set and architecture allow operations
across all banks. The entire data memory may be
accessed by Direct, Indirect or Indexed Addressing
modes. Addressing modes are discussed later in this
subsection.
To ensure that commonly used registers (SFRs and
select GPRs) can be accessed in a single cycle, PIC18
devices implement an Access Bank. This is a 256-byte
memory space that provides fast access to SFRs and
the lower portion of GPR Bank 0 without using the
BSR. Section 5.3.2 “Access Bank” provides a
detailed description of the Access RAM.
5.3.1BANK SELECT REGISTER (BSR)
Large areas of data memory require an efficient
addressing scheme to make rapid access to any
address possible. Ideally, this means that an entire
address does not need to be provided for each read or
write operation. For PIC18 devices, this is accomplished with a RAM banking scheme. This divides the
memory space into 16 contiguous banks of 256 bytes.
Depending on the instruction, each location can be
addressed directly by its full 12-bit address, or an 8-bit
low-order address and a 4-bit bank pointer.
Most instructions in the PIC18 instruction set make use
of the bank pointer, known as the Bank Select Register
(BSR). This SFR holds the 4 Most Significant bits of a
location’s address; the instruction itself includes the
8 Least Significant bits. Only the four lower bits of the
BSR are implemented (BSR3:BSR0). The upper four
bits are unused; they will always read ‘0’ and cannot be
written to. The BSR can be loaded directly by using the
MOVLB instruction.
The value of the BSR indicates the bank in data memory; the 8 bits in the instruction show the location in the
bank and can be thought of as an offset from the bank’s
lower boundary. The relationship between the BSR’s
value and the bank division in data memory is shown in
Figure 5-6.
Since up to 16 registers may share the same low-order
address, the user must always be careful to ensure that
the proper bank is selected before performing a data
read or write. For example, writing what should be
program data to an 8-bit address of F9h while the BSR
is 0Fh, will end up resetting the program counter.
While any bank can be selected, only those banks that
are actually implemented can be read or written to.
Writes to unimplemented banks are ignored, while
reads from unimplemented banks will return ‘0’s. Even
so, the STATUS register will still be affected as if the
operation was successful. The data memory map in
Figure 5-5 indicates which banks are implemented.
In the core PIC18 instruction set, only the MOVFF
instruction fully specifies the 12-bit address of the
source and target registers. This instruction ignores the
BSR completely when it executes. All other instructions
include only the low-order address as an operand and
must use either the BSR or the Access Bank to locate
their target registers.
FIGURE 5-6:USE OF THE BANK SELECT REGISTER (DIRECT ADDRESSING)
Memory
7
BSR
0000
Bank Select
(2)
(1)
0
0011
000h
100h
200h
300h
Data
Bank 0
Bank 1
Bank 2
Bank 3
through
Bank 13
00h
FFh
00h
FFh
00h
FFh
00h
7
From Opcode
11111111
(2)
0
E00h
F00h
FFFh
Note 1:The Access RAM bit of the instruction can be used to force an override of the selected bank (BSR<3:0>) to
the registers of the Access Bank.
2:The MOVFF instruction embeds the entire 12-bit address in the instruction.
Bank 14
Bank 15
5.3.2 ACCESS BANK
While the use of the BSR with an embedded 8-bit
address allows users to address the entire range of
data memory, it also means that the user must always
ensure that the correct bank is selected. Otherwise,
data may be read from or written to the wrong location.
This can be disastrous if a GPR is the intended target
of an operation, but an SFR is written to instead.
Verifying and/or changing the BSR for each read or
write to data memory can become very inefficient.
To streamline access for the most commonly used data
memory locations, the data memory is configured with
an Access Bank, which allows users to access a
mapped block of memory without specifying a BSR.
The Access Bank consists of the first 128 bytes of
memory (00h-7Fh) in Bank 0 and the last 128 bytes of
memory (80h-FFh) in Block 15. The lower half is known
as the “Access RAM” and is composed of GPRs. The
FFh
00h
FFh
00h
FFh
however, the instruction is forced to use the Access
Bank address map; the current value of the BSR is
ignored entirely.
Using this “forced” addressing allows the instruction to
operate on a data address in a single cycle, without
updating the BSR first. For 8-bit addresses of 80h and
above, this means that users can evaluate and operate
on SFRs more efficiently. The Access RAM below 80h
is a good place for data values that the user might need
to access rapidly, such as immediate computational
results or common program variables. Access RAM
also allows for faster and more code efficient context
saving and switching of variables.
The mapping of the Access Bank is slightly different
when the extended instruction set is enabled (XINST
Configuration bit = 1). This is discussed in more detail
in Section 5.6.3 “Mapping the Access Bank inIndexed Literal Offset Mode”.
upper half is also where the device’s SFRs are
mapped. These two areas are mapped contiguously in
the Access Bank and can be addressed in a linear
fashion by an 8-bit address (Figure 5-5).
The Access Bank is used by core PIC18 instructions
that include the Access RAM bit (the ‘a’ parameter in
the instruction). When ‘a’ is equal to ‘1’, the instruction
uses the BSR and the 8-bit address included in the
opcode for the data memory address. When ‘a’ is ‘0’
5.3.3GENERAL PURPOSE
REGISTER FILE
PIC18 devices may have banked memory in the GPR
area. This is data RAM, which is available for use by all
instructions. GPRs start at the bottom of Bank 0
(address 000h) and grow upwards towards the bottom
of the SFR area. GPRs are not initialized by a
Power-on Reset and are unchanged on all other
Resets.
The Special Function Registers (SFRs) are registers
used by the CPU and peripheral modules for controlling
the desired operation of the device. These registers are
implemented as static RAM. SFRs start at the top of
data memory (FFFh) and extend downward to occupy
the top half of Bank 15 (F80h to FFFh). A list of these
registers is given in Table 5-1 and Table 5-2.
The SFRs can be classified into two sets: those
peripheral functions. The reset and interrupt registers
are described in their respective chapters, while the
ALU’s STATUS register is described later in this
section. Registers related to the operation of a
peripheral feature are described in the chapter for that
peripheral.
The SFRs are typically distributed among the
peripherals whose functions they control. Unused SFR
locations are unimplemented and read as ‘0’s.
associated with the “core” device functionality (ALU,
Resets and interrupts) and those related to the
INTCON2RBPU
INTCON3INT2IPINT1IP
INDF0Uses contents of FSR0 to address data memory – value of FSR0 not changed (not a physical register)N/A49, 89
POSTINC0Uses contents of FSR0 to address data memory – value of FSR0 post-incremented (not a physical register)N/A49, 90
POSTDEC0Uses contents of FSR0 to address data memory – value of FSR0 post-decremented (not a physical register)N/A49, 90
PREINC0Uses contents of FSR0 to address data memory – value of FSR0 pre-incremented (not a physical register)N/A49, 90
PLUSW0Uses contents of FSR0 to address data memory – value of FSR0 pre-incremented (not a physical register),
FSR0H
FSR0LIndirect Data Memory Address Pointer 0 Low Bytexxxx xxxx 49, 89
WREGWorking Registerxxxx xxxx49
INDF1Uses contents of FSR1 to address data memory – value of FSR1 not changed (not a physical register)N/A49, 89
POSTINC1Uses contents of FSR1 to address data memory – value of FSR1 post-incremented (not a physical register)N/A49, 90
POSTDEC1Uses contents of FSR1 to address data memory – value of FSR1 post-decremented (not a physical register)N/A49, 90
PREINC1Uses contents of FSR1 to address data memory – value of FSR1 pre-incremented (not a physical register)N/A49, 90
PLUSW1Uses contents of FSR1 to address data memory – value of FSR1 pre-incremented (not a physical register),
FSR1H
FSR1LIndirect Data Memory Address Pointer 1 Low Bytexxxx xxxx 49, 89
BSR
INDF2Uses contents of FSR2 to address data memory – value of FSR2 not changed (not a physical register)N/A50, 89
POSTINC2Uses contents of FSR2 to address data memory – value of FSR2 post-incremented (not a physical register)N/A50, 90
POSTDEC2Uses contents of FSR2 to address data memory – value of FSR2 post-decremented (not a physical register)N/A50, 90
PREINC2Uses contents of FSR2 to address data memory – value of FSR2 pre-incremented (not a physical register)N/A50, 90
PLUSW2Uses contents of FSR2 to address data memory – value of FSR2 pre-incremented (not a physical register),
Legend: x = unknown, u = unchanged, - = unimplemented, q = value depends on condition
Note 1: Bit 21 of the PC is only available in Test mode and Serial Programming modes.
2: The SBOREN bit is only available when CONFIG2L<1:0> = 01; otherwise, it is disabled and reads as ‘0’. See Section 4.4 “Brown-out Reset
(BOR)”.
3: These registers and/or bits are not implemented on PIC18F2X8X devices and are read as ‘0’. Reset values are shown for PIC18F4X8X
devices; individual unimplemented bits should be interpreted as ‘—’.
4: The PLLEN bit is only available in specific oscillator configuration; otherwise, it is disabled and reads as ‘0’. See Section 2.6.4 “PLL in
INTOSC Modes”.
5: The RE3 bit is only available when Master Clear Reset is disabled (CONFIG3H<7> = 0); otherwise, RE3 reads as ‘0’. This bit is read-only.
6: RA6/RA7 and their associated latch and direction bits are individually configured as port pins based on various primary oscillator modes.
When disabled, these bits read as ‘0’.
7: CAN bits have multiple functions depending on the selected mode of the CAN module.
8: This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
9: These registers are available on PIC18F4X8X devices only.
Legend: x = unknown, u = unchanged, - = unimplemented, q = value depends on condition
Note 1: Bit 21 of the PC is only available in Test mode and Serial Programming modes.
2: The SBOREN bit is only available when CONFIG2L<1:0> = 01; otherwise, it is disabled and reads as ‘0’. See Section 4.4 “Brown-out Reset
(BOR)”.
3: These registers and/or bits are not implemented on PIC18F2X8X devices and are read as ‘0’. Reset values are shown for PIC18F4X8X
devices; individual unimplemented bits should be interpreted as ‘—’.
4: The PLLEN bit is only available in specific oscillator configuration; otherwise, it is disabled and reads as ‘0’. See Section 2.6.4 “PLL in
INTOSC Modes”.
5: The RE3 bit is only available when Master Clear Reset is disabled (CONFIG3H<7> = 0); otherwise, RE3 reads as ‘0’. This bit is read-only.
6: RA6/RA7 and their associated latch and direction bits are individually configured as port pins based on various primary oscillator modes.
When disabled, these bits read as ‘0’.
7: CAN bits have multiple functions depending on the selected mode of the CAN module.
8: This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
9: These registers are available on PIC18F4X8X devices only.
TRISCData Direction Control Register for PORTC1111 1111 52, 135
TRISBData Direction Control Register for PORTB1111 1111 52, 132
TRISATRISA7
(3)
LATE
LATD
(3)
—————LAT E2LATE 1LATE0---- -xxx 52, 141
Read PORTD Data Latch, Write PORTD Data Latchxxxx xxxx 52, 138
(6)
TRISA6
(6)
Data Direction Control Register for PORTA1111 1111 52, 129
LATCRead PORTC Data Latch, Write PORTC Data Latchxxxx xxxx 52, 135
LATBRead PORTB Data Latch, Write PORTB Data Latchxxxx xxxx 52, 132
LATALATA7
(6)
LATA6
(6)
Read PORTA Data Latch, Write PORTA Data Latchxxxx xxxx 52, 129
Legend: x = unknown, u = unchanged, - = unimplemented, q = value depends on condition
Note 1: Bit 21 of the PC is only available in Test mode and Serial Programming modes.
2: The SBOREN bit is only available when CONFIG2L<1:0> = 01; otherwise, it is disabled and reads as ‘0’. See Section 4.4 “Brown-out Reset
(BOR)”.
3: These registers and/or bits are not implemented on PIC18F2X8X devices and are read as ‘0’. Reset values are shown for PIC18F4X8X
devices; individual unimplemented bits should be interpreted as ‘—’.
4: The PLLEN bit is only available in specific oscillator configuration; otherwise, it is disabled and reads as ‘0’. See Section 2.6.4 “PLL in
INTOSC Modes”.
5: The RE3 bit is only available when Master Clear Reset is disabled (CONFIG3H<7> = 0); otherwise, RE3 reads as ‘0’. This bit is read-only.
6: RA6/RA7 and their associated latch and direction bits are individually configured as port pins based on various primary oscillator modes.
When disabled, these bits read as ‘0’.
7: CAN bits have multiple functions depending on the selected mode of the CAN module.
8: This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
9: These registers are available on PIC18F4X8X devices only.
Legend: x = unknown, u = unchanged, - = unimplemented, q = value depends on condition
Note 1: Bit 21 of the PC is only available in Test mode and Serial Programming modes.
2: The SBOREN bit is only available when CONFIG2L<1:0> = 01; otherwise, it is disabled and reads as ‘0’. See Section 4.4 “Brown-out Reset
(BOR)”.
3: These registers and/or bits are not implemented on PIC18F2X8X devices and are read as ‘0’. Reset values are shown for PIC18F4X8X
devices; individual unimplemented bits should be interpreted as ‘—’.
4: The PLLEN bit is only available in specific oscillator configuration; otherwise, it is disabled and reads as ‘0’. See Section 2.6.4 “PLL in
INTOSC Modes”.
5: The RE3 bit is only available when Master Clear Reset is disabled (CONFIG3H<7> = 0); otherwise, RE3 reads as ‘0’. This bit is read-only.
6: RA6/RA7 and their associated latch and direction bits are individually configured as port pins based on various primary oscillator modes.
When disabled, these bits read as ‘0’.
7: CAN bits have multiple functions depending on the selected mode of the CAN module.
8: This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
9: These registers are available on PIC18F4X8X devices only.
Legend: x = unknown, u = unchanged, - = unimplemented, q = value depends on condition
Note 1: Bit 21 of the PC is only available in Test mode and Serial Programming modes.
2: The SBOREN bit is only available when CONFIG2L<1:0> = 01; otherwise, it is disabled and reads as ‘0’. See Section 4.4 “Brown-out Reset
(BOR)”.
3: These registers and/or bits are not implemented on PIC18F2X8X devices and are read as ‘0’. Reset values are shown for PIC18F4X8X
devices; individual unimplemented bits should be interpreted as ‘—’.
4: The PLLEN bit is only available in specific oscillator configuration; otherwise, it is disabled and reads as ‘0’. See Section 2.6.4 “PLL in
INTOSC Modes”.
5: The RE3 bit is only available when Master Clear Reset is disabled (CONFIG3H<7> = 0); otherwise, RE3 reads as ‘0’. This bit is read-only.
6: RA6/RA7 and their associated latch and direction bits are individually configured as port pins based on various primary oscillator modes.
When disabled, these bits read as ‘0’.
7: CAN bits have multiple functions depending on the selected mode of the CAN module.
8: This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
9: These registers are available on PIC18F4X8X devices only.
Legend: x = unknown, u = unchanged, - = unimplemented, q = value depends on condition
Note 1: Bit 21 of the PC is only available in Test mode and Serial Programming modes.
2: The SBOREN bit is only available when CONFIG2L<1:0> = 01; otherwise, it is disabled and reads as ‘0’. See Section 4.4 “Brown-out Reset
(BOR)”.
3: These registers and/or bits are not implemented on PIC18F2X8X devices and are read as ‘0’. Reset values are shown for PIC18F4X8X
devices; individual unimplemented bits should be interpreted as ‘—’.
4: The PLLEN bit is only available in specific oscillator configuration; otherwise, it is disabled and reads as ‘0’. See Section 2.6.4 “PLL in
INTOSC Modes”.
5: The RE3 bit is only available when Master Clear Reset is disabled (CONFIG3H<7> = 0); otherwise, RE3 reads as ‘0’. This bit is read-only.
6: RA6/RA7 and their associated latch and direction bits are individually configured as port pins based on various primary oscillator modes.
When disabled, these bits read as ‘0’.
7: CAN bits have multiple functions depending on the selected mode of the CAN module.
8: This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
9: These registers are available on PIC18F4X8X devices only.
Legend: x = unknown, u = unchanged, - = unimplemented, q = value depends on condition
Note 1: Bit 21 of the PC is only available in Test mode and Serial Programming modes.
2: The SBOREN bit is only available when CONFIG2L<1:0> = 01; otherwise, it is disabled and reads as ‘0’. See Section 4.4 “Brown-out Reset
(BOR)”.
3: These registers and/or bits are not implemented on PIC18F2X8X devices and are read as ‘0’. Reset values are shown for PIC18F4X8X
devices; individual unimplemented bits should be interpreted as ‘—’.
4: The PLLEN bit is only available in specific oscillator configuration; otherwise, it is disabled and reads as ‘0’. See Section 2.6.4 “PLL in
INTOSC Modes”.
5: The RE3 bit is only available when Master Clear Reset is disabled (CONFIG3H<7> = 0); otherwise, RE3 reads as ‘0’. This bit is read-only.
6: RA6/RA7 and their associated latch and direction bits are individually configured as port pins based on various primary oscillator modes.
When disabled, these bits read as ‘0’.
7: CAN bits have multiple functions depending on the selected mode of the CAN module.
8: This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
9: These registers are available on PIC18F4X8X devices only.
Legend: x = unknown, u = unchanged, - = unimplemented, q = value depends on condition
Note 1: Bit 21 of the PC is only available in Test mode and Serial Programming modes.
2: The SBOREN bit is only available when CONFIG2L<1:0> = 01; otherwise, it is disabled and reads as ‘0’. See Section 4.4 “Brown-out Reset
(BOR)”.
3: These registers and/or bits are not implemented on PIC18F2X8X devices and are read as ‘0’. Reset values are shown for PIC18F4X8X
devices; individual unimplemented bits should be interpreted as ‘—’.
4: The PLLEN bit is only available in specific oscillator configuration; otherwise, it is disabled and reads as ‘0’. See Section 2.6.4 “PLL in
INTOSC Modes”.
5: The RE3 bit is only available when Master Clear Reset is disabled (CONFIG3H<7> = 0); otherwise, RE3 reads as ‘0’. This bit is read-only.
6: RA6/RA7 and their associated latch and direction bits are individually configured as port pins based on various primary oscillator modes.
When disabled, these bits read as ‘0’.
7: CAN bits have multiple functions depending on the selected mode of the CAN module.
8: This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
9: These registers are available on PIC18F4X8X devices only.
Legend: x = unknown, u = unchanged, - = unimplemented, q = value depends on condition
Note 1: Bit 21 of the PC is only available in Test mode and Serial Programming modes.
2: The SBOREN bit is only available when CONFIG2L<1:0> = 01; otherwise, it is disabled and reads as ‘0’. See Section 4.4 “Brown-out Reset
(BOR)”.
3: These registers and/or bits are not implemented on PIC18F2X8X devices and are read as ‘0’. Reset values are shown for PIC18F4X8X
devices; individual unimplemented bits should be interpreted as ‘—’.
4: The PLLEN bit is only available in specific oscillator configuration; otherwise, it is disabled and reads as ‘0’. See Section 2.6.4 “PLL in
INTOSC Modes”.
5: The RE3 bit is only available when Master Clear Reset is disabled (CONFIG3H<7> = 0); otherwise, RE3 reads as ‘0’. This bit is read-only.
6: RA6/RA7 and their associated latch and direction bits are individually configured as port pins based on various primary oscillator modes.
When disabled, these bits read as ‘0’.
7: CAN bits have multiple functions depending on the selected mode of the CAN module.
8: This register reads all ‘0’s until the ECAN™ technology is set up in Mode 1 or Mode 2.
9: These registers are available on PIC18F4X8X devices only.
The STATUS register, shown in Register 5-2, contains
the arithmetic status of the ALU. As with any other SFR,
it can be the operand for any instruction.
If the STATUS register is the destination for an instruction that affects the Z, DC, C, OV or N bits, the results
of the instruction are not written; instead, the status is
updated according to the instruction performed. Therefore, the result of an instruction with the STATUS
register as its destination may be different than
intended. As an example, CLRF STATUS will set the Z
bit and leave the remaining Status bits unchanged
(‘000u u1uu’).
REGISTER 5-2:STATUS REGISTER
U-0U-0U-0R/W-xR/W-xR/W-xR/W-xR/W-x
———NOVZDCC
bit 7bit 0
bit 7-5Unimplemented: Read as ‘0’
bit 4N: Negative bit
This bit is used for signed arithmetic (2’s complement). It indicates whether the result was
negative (ALU MSB = 1).
1 = Result was negative
0 = Result was positive
bit 3OV: Overflow bit
This bit is used for signed arithmetic (2’s complement). It indicates an overflow of the 7-bit
magnitude which causes the sign bit (bit 7) to change state.
1 = Overflow occurred for signed arithmetic (in this arithmetic operation)
0 = No overflow occurred
bit 2Z: Zero bit
1 = The result of an arithmetic or logic operation is zero
0 = The result of an arithmetic or logic operation is not zero
bit 1DC: Digit carry/borrow
For ADDWF, ADDLW, SUBLW and SUBWF instructions:
1 = A carry-out from the 4th low-order bit of the result occurred
0 = No carry-out from the 4th low-order bit of the result
Note:For borrow,
complement of the second operand. For rotate (RRF, RLF) instructions, this bit is
loaded with either the bit 4 or bit 3 of the source register.
bit 0C: Carry/borrow
For ADDWF, ADDLW, SUBLW and SUBWF instructions:
1 = A carry-out from the Most Significant bit of the result occurred
0 = No carry-out from the Most Significant bit of the result occurred
Note:For borrow,
complement of the second operand. For rotate (RRF, RLF) instructions, this bit is
loaded with either the high or low-order bit of the source register.
bit
the polarity is reversed. A subtraction is executed by adding the two’s
bit
the polarity is reversed. A subtraction is executed by adding the two’s
It is recommended that only BCF, BSF, SWAPF, MOVFF
and MOVWF instructions are used to alter the STATUS
register, because these instructions do not affect the Z,
C, DC, OV or N bits in the STATUS register.
For other instructions that do not affect Status bits, see
the instruction set summaries in Table 25-2 and
Table 25-3.
Note:The C and DC bits operate as the borrow
and digit borrow bits respectively in
subtraction.
Legend:
R = Readable bitW = Writable bitU = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set‘0’ = Bit is clearedx = Bit is unknown
core PIC18 instruction set are changed
when the PIC18 extended instruction
set is enabled. See Section 5.6 “Data
Memory and the Extended Instruction
Set” for more information.
While the program memory can be addressed in only
one way – through the program counter – information
in the data memory space can be addressed in several
ways. For most instructions, the addressing mode is
fixed. Other instructions may use up to three modes,
depending on which operands are used and whether or
not the extended instruction set is enabled.
The addressing modes are:
• Inherent
• Literal
•Direct
•Indirect
An additional addressing mode, Indexed Literal Offset,
is available when the extended instruction set is
enabled (XINST Configuration bit = 1). Its operation is
discussed in greater detail in Section 5.6.1 “IndexedAddressing with Literal Offset”.
5.4.1INHERENT AND LITERAL
ADDRESSING
Many PIC18 control instructions do not need any
argument at all; they either perform an operation that
globally affects the device or they operate implicitly on
one register. This addressing mode is known as
Inherent Addressing. Examples include SLEEP, RESET
and DAW.
Other instructions work in a similar way but require an
additional explicit argument in the opcode. This is
known as Literal Addressing mode because they
require some literal value as an argument. Examples
include ADDLW and MOVLW which, respectively, add or
move a literal value to the W register. Other examples
include CALL and GOTO, which include a 20-bit
program memory address.
5.4.2DIRECT ADDRESSING
Direct addressing specifies all or part of the source
and/or destination address of the operation within the
opcode itself. The options are specified by the
arguments accompanying the instruction.
In the core PIC18 instruction set, bit-oriented and
byte-oriented instructions use some version of direct
addressing by default. All of these instructions include
some 8-bit literal address as their Least Significant
Byte. This address specifies either a register address in
one of the banks of data RAM (Section 5.3.3 “General
Purpose Register File”) or a location in the Access
Bank (Section 5.3.2 “Access Bank”) as the data
source for the instruction.
The Access RAM bit ‘a’ determines how the address is
interpreted. When ‘a’ is ‘1’, the contents of the BSR
(Section 5.3.1 “Bank Select Register (BSR)”) are
used with the address to determine the complete 12-bit
address of the register. When ‘a’ is ‘0’, the address is
interpreted as being a register in the Access Bank.
Addressing that uses the Access RAM is sometimes
also known as Direct Forced Addressing mode.
A few instructions, such as MOVFF, include the entire
12-bit address (either source or destination) in their
opcodes. In those cases, the BSR is ignored entirely.
The destination of the operation’s results is determined
by the destination bit ‘d’. When ‘d’ is ‘1’, the results are
stored back in the source register, overwriting its original contents. When ‘d’ is ‘0’, the results are stored in
the W register. Instructions without the ‘d’ argument
have a destination that is implicit in the instruction; their
destination is either the target register being operated
on or the W register.
5.4.3INDIRECT ADDRESSING
Indirect addressing allows the user to access a location
in data memory without giving a fixed address in the
instruction. This is done by using File Select Registers
(FSRs) as pointers to the locations to be read or written
to. Since the FSRs are themselves located in RAM as
Special File Registers, they can also be directly manipulated under program control. This makes FSRs very
useful in implementing data structures, such as tables
and arrays in data memory.
The registers for indirect addressing are also implemented with Indirect File Operands (INDFs) that permit
automatic manipulation of the pointer value with
auto-incrementing, auto-decrementing or offsetting
with another value. This allows for efficient code, using
loops, such as the example of clearing an entire RAM
bank in Example 5-5.
At the core of indirect addressing are three sets of
registers: FSR0, FSR1 and FSR2. Each represents a
pair of 8-bit registers, FSRnH and FSRnL. The four
upper bits of the FSRnH register are not used, so each
FSR pair holds a 12-bit value. This represents a value
that can address the entire range of the data memory
in a linear fashion. The FSR register pairs, then, serve
as pointers to data memory locations.
Indirect addressing is accomplished with a set of
Indirect File Operands, INDF0 through INDF2. These
can be thought of as “virtual” registers: they are
FIGURE 5-7:INDIRECT ADDRESSING
Using an instruction with one of the
indirect addressing registers as the
operand....
...uses the 12-bit address stored in
the FSR pair associated with that
register....
xxxx1110 11001100
ADDWF, INDF1, 1
mapped in the SFR space, but are not physically
implemented. Reading or writing to a particular INDF
register actually accesses its corresponding FSR
register pair. A read from INDF1, for example, reads
the data at the address indicated by FSR1H:FSR1L.
Instructions that use the INDF registers as operands
actually use the contents of their corresponding FSR as
a pointer to the instruction’s target. The INDF operand
is just a convenient way of using the pointer.
Because indirect addressing uses a full 12-bit address,
data RAM banking is not necessary. Thus, the current
contents of the BSR and the Access RAM bit have no
effect on determining the target address.
FSR1H:FSR1L
07
7
000h
Bank 0
100h
200h
300h
0
Bank 1
Bank 2
Bank 3
through
Bank 13
...to determine the data memory
location to be used in that operation.
In this case, the FSR1 pair contains
ECCh. This means the contents of
location ECCh will be added to that
of the W register and stored back in
ECCh.
5.4.3.2FSR Registers and POSTINC,
POSTDEC, PREINC and PLUSW
In addition to the INDF operand, each FSR register pair
also has four additional indirect operands. Like INDF,
these are “virtual” registers that cannot be indirectly
read or written to. Accessing these registers actually
accesses the associated FSR register pair, but also
performs a specific action on its stored value. They are:
• POSTDEC: accesses the FSR value, then
automatically decrements it by 1 afterwards
• POSTINC: accesses the FSR value, then
automatically increments it by 1 afterwards
• PREINC: increments the FSR value by 1, then
uses it in the operation
• PLUSW: adds the signed value of the W register
(range of -127 to 128) to that of the FSR and uses
the new value in the operation.
In this context, accessing an INDF register uses the
value in the FSR registers without changing them.
Similarly, accessing a PLUSW register gives the FSR
value offset by that in the W register; neither value is
actually changed in the operation. Accessing the other
virtual registers changes the value of the FSR
registers.
Operations on the FSRs with POSTDEC, POSTINC
and PREINC affect the entire register pair; that is,
rollovers of the FSRnL register from FFh to 00h carry
over to the FSRnH register. On the other hand, results
of these operations do not change the value of any
flags in the STATUS register (e.g., Z, N, OV, etc.).
The PLUSW register can be used to implement a form
of indexed addressing in the data memory space. By
manipulating the value in the W register, users can
reach addresses that are fixed offsets from pointer
addresses. In some applications, this can be used to
implement some powerful program control structure,
such as software stacks, inside of data memory.
5.4.3.3Operations by FSRs on FSRs
Indirect addressing operations that target other FSRs
or virtual registers represent special cases. For example, using an FSR to point to one of the virtual registers
will not result in successful operations. As a specific
case, assume that FSR0H:FSR0L contains FE7h, the
address of INDF1. Attempts to read the value of the
INDF1 using INDF0 as an operand will return 00h.
Attempts to write to INDF1 using INDF0 as the operand
will result in a NOP.
On the other hand, using the virtual registers to write to
an FSR pair may not occur as planned. In these cases,
the value will be written to the FSR pair but without any
incrementing or decrementing. Thus, writing to INDF2
or POSTDEC2 will write the same value to the
FSR2H:FSR2L.
Since the FSRs are physical registers mapped in the
SFR space, they can be manipulated through all direct
operations. Users should proceed cautiously when
working on these registers, particularly if their code
uses indirect addressing.
Similarly, operations by indirect addressing are generally permitted on all other SFRs. Users should exercise
the appropriate caution that they do not inadvertently
change settings that might affect the operation of the
device.
5.5Program Memory and the
Extended Instruction Set
The operation of program memory is unaffected by the
use of the extended instruction set.
Enabling the extended instruction set adds eight
additional two-word commands to the existing
PIC18 instruction set: ADDFSR, ADDULNK, CALLW,
MOVSF, MOVSS, PUSHL, SUBFSR and SUBULNK. These
instructions are executed as described in
Section 5.2.4 “Two-Word Instructions”.
5.6Data Memory and the Extended
Instruction Set
Enabling the PIC18 extended instruction set (XINST
Configuration bit = 1) significantly changes certain
aspects of data memory and its addressing. Specifically, the use of the Access Bank for many of the core
PIC18 instructions is different; this is due to the introduction of a new addressing mode for the data memory
space. This mode also alters the behavior of indirect
addressing using FSR2 and its associated operands.
What does not change is just as important. The size of
the data memory space is unchanged, as well as its
linear addressing. The SFR map remains the same.
Core PIC18 instructions can still operate in both Direct
and Indirect Addressing mode; inherent and literal
instructions do not change at all. Indirect addressing
with FSR0 and FSR1 also remains unchanged.
5.6.1INDEXED ADDRESSING WITH
LITERAL OFFSET
Enabling the PIC18 extended instruction set changes
the behavior of indirect addressing using the FSR2
register pair and its associated file operands. Under the
proper conditions, instructions that use the Access
Bank – that is, most bit-oriented and byte-oriented –
instructions – can invoke a form of indexed addressing
using an offset specified in the instruction. This special
addressing mode is known as Indexed Addressing with
Literal Offset or Indexed Literal Offset mode.
When using the extended instruction set, this
addressing mode requires the following:
• The use of the Access Bank is forced (‘a’ = 0);
and
• The file address argument is less than or equal to
5Fh.
Under these conditions, the file address of the instruction is not interpreted as the lower byte of an address
(used with the BSR in direct addressing), or as an 8-bit
address in the Access Bank. Instead, the value is
interpreted as an offset value to an address pointer,
specified by FSR2. The offset and the contents of
FSR2 are added to obtain the target address of the
operation.
5.6.2INSTRUCTIONS AFFECTED BY
INDEXED LITERAL OFFSET MODE
Any of the core PIC18 instructions that can use direct
addressing are potentially affected by the Indexed
Literal Offset Addressing mode. This includes all
byte-oriented and bit-oriented instructions, or almost
one-half of the standard PIC18 instruction set. Instructions that only use Inherent or Literal Addressing
modes are unaffected.
Additionally, byte-oriented and bit-oriented instructions
are not affected if they use the Access Bank (Access
RAM bit is ‘1’), or include a file address of 60h or above.
Instructions meeting these criteria will continue to
execute as before. A comparison of the different possible addressing modes when the extended instruction
set is enabled in shown in Figure 5-8.
Those who desire to use byte-oriented or bit-oriented
instructions in the Indexed Literal Offset mode should
note the changes to assembler syntax for this mode.
This is described in more detail in Section 25.2.1“Extended Instruction Syntax”.
FIGURE 5-8:COMPARING ADDRESSING OPTIONS FOR BIT-ORIENTED AND
BYTE-ORIENTED INSTRUCTIONS (EXTENDED INSTRUCTION SET ENABLED)
EXAMPLE INSTRUCTION: ADDWF, f, d, a (Opcode: 0010 01da ffff ffff)
When a = 0 and f ≥ 60h:
The instruction executes in
Direct Forced mode. ‘f’ is
interpreted as a location in the
Access RAM between 060h
and 0FFh. This is the same as
the SFRs, or locations F60h to
0FFh (Bank 15) of data
memory.
Locations below 60h are not
available in this addressing
mode.
When a = 0 and f ≤ 5Fh:
The instruction executes in
Indexed Literal Offset mode. ‘f’
is interpreted as an offset to the
address value in FSR2. The
two are added together to
obtain the address of the target
register for the instruction. The
address can be anywhere in
the data memory space.
Note that in this mode, the
correct syntax is now:
ADDWF [k], d
where ‘k’ is the same as ‘f’.
000h
060h
080h
100h
F00h
F60h
FFFh
000h
080h
100h
F00h
F60h
FFFh
Bank 0
Bank 1
through
Bank 14
Bank 15
SFRs
Data Memory
Bank 0
Bank 1
through
Bank 14
Bank 15
SFRs
Data Memory
00h
60h
Access RAM
FSR2HFSR2L
FFh
ffffffff001001da
Valid range
for ‘f’
BSR
00000000
ffffffff001001da
When a = 1 (all values of f):
The instruction executes in
Direct mode (also known as
Direct Long mode). ‘f’ is
interpreted as a location in
one of the 16 banks of the data
memory space. The bank is
designated by the Bank Select
000h
080h
100h
Bank 0
Bank 1
through
Bank 14
Register (BSR). The address
can be in any implemented
bank in the data memory
space.
5.6.3MAPPING THE ACCESS BANK IN
INDEXED LITERAL OFFSET MODE
The use of Indexed Literal Offset Addressing mode
effectively changes how the lower half of Access RAM
(00h to 7Fh) is mapped. Rather than containing just the
contents of the bottom half of Bank 0, this mode maps
the contents from Bank 0 and a user defined “window”
that can be located anywhere in the data memory
space. The value of FSR2 establishes the lower boundary of the addresses mapped into the window, while the
upper boundary is defined by FSR2 plus 95 (5Fh).
Addresses in the Access RAM above 5Fh are mapped
as previously described (see Section 5.3.2 “AccessBank”). An example of Access Bank remapping in this
addressing mode is shown in Figure 5-9.
FIGURE 5-9:REMAPPING THE ACCESS BANK WITH INDEXED LITERAL
OFFSET ADDRESSING
Remapping of the Access Bank applies
tions using the Indexed Literal Offset mode. Operations
that use the BSR (Access RAM bit is ‘1’) will continue
to use direct addressing as before. Any indirect or
indexed operation that explicitly uses any of the indirect
file operands (including FSR2) will continue to operate
as standard indirect addressing. Any instruction that
uses the Access Bank, but includes a register address
of greater than 05Fh, will use direct addressing and the
normal Access Bank map.
5.6.4BSR IN INDEXED LITERAL
OFFSET MODE
Although the Access Bank is remapped when the
extended instruction set is enabled, the operation of the
BSR remains unchanged. Direct addressing using the
BSR to select the data memory bank operates in the
same manner as previously described.
only
to opera-
Example Situation:
ADDWF f, d, a
FSR2H:FSR2L = 120h
Locations in the region
from the FSR2 pointer
(120h) to the pointer plus
05Fh (17Fh) are mapped
to the bottom of the
Access RAM (000h-05Fh).
Special File Registers at
F60h through FFFh are
mapped to 60h through
FFh, as usual.
Bank 0 addresses below
5Fh are not available in
this mode. They can still
be addressed by using the
BSR.
The Flash program memory is readable, writable and
erasable during normal operation over the entire V
range.
A read from program memory is executed on one byte
at a time. A write to program memory is executed on
blocks of 64 bytes at a time. Program memory is
erased in blocks of 64 bytes at a time. A bulk erase
operation may not be issued from user code.
Writing or erasing program memory will cease
instruction fetches until the operation is complete. The
program memory cannot be accessed during the write
or erase, therefore, code cannot execute. An internal
programming timer terminates program memory writes
and erases.
A value written to program memory does not need to be
a valid instruction. Executing a program memory
location that forms an invalid instruction results in a
NOP.
DD
6.1Table Reads and Table Writes
In order to read and write program memory, there are
two operations that allow the processor to move bytes
between the program memory space and the data RAM:
• Table Read (TBLRD)
• Table Write (TBLWT)
The program memory space is 16 bits wide, while the
data RAM space is 8 bits wide. Table reads and table
writes move data between these two memory spaces
through an 8-bit register (TABLAT).
Table read operations retrieve data from program
memory and place it into the data RAM space.
Figure 6-1 shows the operation of a table read with
program memory and data RAM.
Table write operations store data from the data memory
space into holding registers in program memory. The
procedure to write the contents of the holding registers
into program memory is detailed in Section 6.5 “Writingto Flash Program Memory”. Figure6-2 shows the
operation of a table write with program memory and data
RAM.
Table operations work with byte entities. A table block
containing data, rather than program instructions, is not
required to be word aligned. Therefore, a table block can
start and end at any byte address. If a table write is being
used to write executable code into program memory,
program instructions will need to be word aligned.
FIGURE 6-1:TABLE READ OPERATION
Table Pointer
TBLPTRU
Note 1: Table Pointer register points to a byte in program memory.
Note 1: Table Pointer actually points to one of 64 holding registers, the address of which is determined by
TBLPTRHTBLPTRL
TBLPTRL<5:0>. The process for physically writing data to the program memory array is discussed in
Section 6.5 “Writing to Flash Program Memory”.
(1)
Program Memory
(TBLPTR)
Holding Registers
Table Latch (8-bit)
TAB LAT
6.2Control Registers
Several control registers are used in conjunction with
the TBLRD and TBLWT instructions. These include the:
• EECON1 register
• EECON2 register
• TABLAT register
• TBLPTR registers
6.2.1EECON1 AND EECON2 REGISTERS
The EECON1 register (Register 6-1) is the control
register for memory accesses. The EECON2 register is
not a physical register; it is used exclusively in the
memory write and erase sequences. Reading
EECON2 will read all ‘0’s.
The EEPGD control bit determines if the access will be
a program or data EEPROM memory access. When
clear, any subsequent operations will operate on the
data EEPROM memory. When set, any subsequent
operations will operate on the program memory.
The CFGS control bit determines if the access will be
to the Configuration/Calibration registers or to program
memory/data EEPROM memory. When set,
subsequent operations will operate on Configuration
registers regardless of EEPGD (see Section 24.0“Special Features of the CPU”). When clear, memory
selection access is determined by EEPGD.
The FREE bit, when set, will allow a program memory
erase operation. When FREE is set, the erase operation is initiated on the next WR command. When FREE
is clear, only writes are enabled.
The WREN bit, when set, will allow a write operation.
On power-up, the WREN bit is clear. The WRERR bit is
set in hardware when the WREN bit is set and cleared
when the internal programming timer expires and the
write operation is complete.
Note:During normal operation, the WRERR is
read as ‘1’. This can indicate that a write
operation was prematurely terminated by
a Reset, or a write operation was
attempted improperly.
The WR control bit initiates write operations. The bit
cannot be cleared, only set, in software; it is cleared in
hardware at the completion of the write operation.
Note:The EEIF Interrupt flag bit (PIR2<4>) is set
when the write is complete. It must be
cleared in software.
The Table Latch (TABLAT) is an 8-bit register mapped
into the SFR space. The Table Latch register is used to
hold 8-bit data during data transfers between program
memory and data RAM.
6.2.3TBLPTR – TABLE POINTER
REGISTER
The Table Pointer (TBLPTR) register addresses a byte
within the program memory. The TBLPTR is comprised
of three SFR registers: Table Pointer Upper Byte, Table
Pointer High Byte and Table Pointer Low Byte
(TBLPTRU:TBLPTRH:TBLPTRL). These three registers join to form a 22-bit wide pointer. The low-order
21 bits allow the device to address up to 2 Mbytes of
program memory space. The 22nd bit allows access to
the device ID, the user ID and the Configuration bits.
The Table Pointer, TBLPTR, is used by the TBLRD and
TBLWT instructions. These instructions can update the
TBLPTR in one of four ways based on the table operation. These operations are shown in Table 6-1. These
operations on the TBLPTR only affect the low-order
21 bits.
6.2.4TABLE POINTER BOUNDARIES
TBLPTR is used in reads, writes and erases of the
Flash program memory.
When a TBLRD is executed, all 22 bits of the TBLPTR
determine which byte is read from program memory
into TABLAT.
When a TBLWT is executed, the six LSbs of the Table
Pointer register (TBLPTR<5:0>) determine which of the
64 program memory holding registers is written to.
When the timed write to program memory begins (via
the WR bit), the 16 MSbs of the TBLPTR
(TBLPTR<21:6>) determine which program memory
block of 64 bytes is written to. For more detail, see
Section 6.5 “Writing to Flash Program Memory”.
When an erase of program memory is executed, the
16 MSbs of the Table Pointer register (TBLPTR<21:6>)
point to the 64-byte block that will be erased. The Least
Significant bits (TBLPTR<5:0>) are ignored.
Figure 6-3 describes the relevant boundaries of
TBLPTR based on Flash program memory operations.
TABLE 6-1:TABLE POINTER OPERATIONS WITH TBLRD AND TBLWT INSTRUCTIONS
ExampleOperation on Table Pointer
TBLRD*
TBLWT*
TBLRD*+
TBLWT*+
TBLRD*TBLWT*-
TBLRD+*
TBLWT+*
TBLPTR is incremented after the read/write
TBLPTR is decremented after the read/write
TBLPTR is incremented before the read/write
TBLPTR is not modified
FIGURE 6-3:TABLE POINTER BOUNDARIES BASED ON OPERATION