Philips 89c51, 89c52, 89c54, 89c58 DATASHEETS
INTEGRATED CIRCUITS
89C51/89C52/89C54/89C58
80C51 8-bit microcontroller family
4K/8K/16K/32K Flash
Product specification
Replaces Datasheets 89C51 of 1999 Apr 01 and 89C52/89C54/89C58 of 1999 Apr 01
1999 Oct 27
Philips Semiconductors Product specification
80C51 8-bit microcontroller family
4K/8K/16K/32K Flash
DESCRIPTION
The 89C51/89C52/89C54/89C58 contain a non-volatile FLASH
program memory that is parallel programmable. For devices that are
serial programmable (In System Programmable (ISP) with a boot
loader), see the 89C51RC+/89C51RD+ datasheet.
Both families are Single-Chip 8-bit Microcontrollers manufactured in
advanced CMOS process and are derivatives of the 80C51
microcontroller family. All the devices have the same instruction set
as the 80C51.
SELECTION T ABLE FOR FLASH DEVICES
ROM/EPROM
Memory Size
(X by 8)
Multi-Time Programmable (MTP) devices:
89C51
4 k 128 No No
89C52/54/58
8 k/16 k/32 k 256 No No
Serial In-System Programmable devices:
89C51RC+
32 k 512 Yes Yes
89C51RD+
64 k 1024 Yes Yes
RAM Size
(X by 8)
Programmable
Timer Counter
(PCA)
Hardware
Watchdog
Timer
89C51/89C52/89C54/89C58
FEATURES
•80C51 Central Processing Unit
•On-chip FLASH Program Memory
•Speed up to 33 MHz
•Full static operation
•RAM expandable externally to 64 k bytes
•4 level priority interrupt
•6 interrupt sources
•Four 8-bit I/O ports
•Full-duplex enhanced UART
– Framing error detection
– Automatic address recognition
•Power control modes
– Clock can be stopped and resumed
– Idle mode
– Power down mode
•Programmable clock out
•Second DPTR register
•Asynchronous port reset
•Low EMI (inhibit ALE)
•3 16-bit timers
•Wake up from power down by an external interrupt
ORDERING INFORMATION
MEMORY SIZE
4 k × 8
FLASH P89C51UBA A P89C52UBA A P89C54UBA A P89C58UBA A
FLASH P89C51UBP N P89C52UBP N P89C54UBP N P89C58UBP N
FLASH P89C51UBB B P89C52UBB B P89C54UBB B P89C58UBB B
FLASH P89C51UFA A P89C52UFA A P89C54UFA A P89C58UFA A
FLASH P89C51UFP N P89C52UFP N P89C54UFP N P89C58UFP N
FLASH P89C51UFB B P89C52UFB B P89C54UFB B P89C58UFB B
NOTES:
1. Contact Philips Sales for availability.
2. SOT not assigned for this package outline.
MEMORY SIZE
8 k × 8
MEMORY SIZE
16 k × 8
MEMORY SIZE
32 k × 8
TEMPERATURE
RANGE °C
AND PACKAGE
0 to +70, Plastic
Leaded Chip Carrier
0 to +70, Plastic
Dual In-line Package
0 to +70, Plastic
Quad Flat Pack
–40 to +85, Plastic
1
Leaded Chip Carrier
–40 to +85, Plastic
1
Dual In-line Package
–40 to +85, Plastic
1
Quad Flat Pack
VOLTAGE
RANGE
5 V 0 to 33 SOT187-2
5 V 0 to 33 SOT129-1
5 V 0 to 33 QFP44
5 V 0 to 33 SOT187-2
5 V 0 to 33 SOT129-1
5 V 0 to 33 QFP44
FREQ.
(MHz)
P ART NUMBER DERIVATION
DEVICE NUMBER (P89CXX) OPERATING FREQUENCY, MAX (V) TEMPERATURE RANGE (B) PACKAGE (AA, BB, PN)
P89C51 FLASH
P89C52 FLASH
P89C54 FLASH
P89C58 FLASH
U = 33 MHz
B = 0_C to 70_C
F = –40_C to 85_C
AA = PLCC
BB = PQFP
PN = PDIP
DWG.
#
2
2
1999 Oct 27 853–2148 22592
2
Philips Semiconductors Product specification
80C51 8-bit microcontroller family
4K/8K/16K/32K Flash
BLOCK DIAGRAM
V
CC
V
SS
RAM ADDR
REGISTER
B
REGISTER
RAM
ACC
TMP2
P0.0–P0.7 P2.0–P2.7
PORT 0
DRIVERS
PORT 0
LATCH
TMP1
PORT 2
DRIVERS
PORT 2
LATCH
89C51/89C52/89C54/89C58
FLASH
8
STACK
POINTER
PROGRAM
ADDRESS
REGISTER
PSEN
EAV
ALE
PP
RST
TIMING
AND
CONTROL
OSCILLATOR
XTAL1 XTAL2
INSTRUCTION
PD
REGISTER
PSW
PORT 1
LATCH
PORT 1
DRIVERS
P1.0–P1.7
ALU
SFRs
TIMERS
PORT 3
LATCH
PORT 3
DRIVERS
P3.0–P3.7
BUFFER
PC
INCRE-
MENTER
8 16
PROGRAM
COUNTER
DPTR’S
MULTIPLE
SU01066
1999 Oct 27
3
Philips Semiconductors Product specification
80C51 8-bit microcontroller family
4K/8K/16K/32K Flash
LOGIC SYMBOL
V
V
SS
CC
XTAL1
ADDRESS AND
PORT 0
XTAL2
RST
EA/V
PP
PSEN
ALE/PROG
RxD
TxD
INT0
INT1
T0
PORT 3
T1
WR
RD
SECONDARY FUNCTIONS
PIN CONFIGURA TIONS
Dual In-Line Package Pin Functions
DATA BUS
T2
T2EX
PORT 1PORT 2
ADDRESS BUS
SU00830
89C51/89C52/89C54/89C58
Ceramic and Plastic Leaded Chip Carrier
Pin Functions
6140
7
17
Pin Function
1 NIC*
2 P1.0/T2
3 P1.1/T2EX
4 P1.2
5 P1.3
6 P1.4
7 P1.5
8 P1.6
9 P1.7
10 RST
11 P3.0/RxD
12 NIC*
13 P3.1/TxD
14 P3.2/INT0
15 P3.3/INT1
* NO INTERNAL CONNECTION
LCC
18 28
Pin Function
16 P3.4/T0
17 P3.5/T1
18 P3.6/WR
19 P3.7/RD
20 XTAL2
21 XTAL1
22 V
SS
23 NIC*
24 P2.0/A8
25 P2.1/A9
26 P2.2/A10
27 P2.3/A11
28 P2.4/A12
29 P2.5/A13
30 P2.6/A14
39
29
Pin Function
31 P2.7/A15
32 PSEN
33 ALE
34 NIC*
35 EA/V
36 P0.7/AD7
37 P0.6/AD6
38 P0.5/AD5
39 P0.4/AD4
40 P0.3/AD3
41 P0.2/AD2
42 P0.1/AD1
43 P0.0/AD0
44 V
PP
CC
SU01062
T2/P1.0
T2EX/P1.1
P1.2
P1.3
P1.4
P1.5
P1.6
P1.7
RST
RxD/P3.0
TxD/P3.1
INT0
/P3.2
/P3.3
INT1
T0/P3.4
T1/P3.5
/P3.6
WR
RD
/P3.7
XTAL2
XTAL1
V
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
SU01063
V
CC
P0.0/AD0
P0.1/AD1
P0.2/AD2
P0.3/AD3
P0.4/AD4
P0.5/AD5
P0.6/AD6
P0.7/AD7
EA
/V
PP
ALE
PSEN
P2.7/A15
P2.6/A14
P2.5/A13
P2.4/A12
P2.3/A11
P2.2/A10
P2.1/A9
P2.0/A8
Plastic Quad Flat Pack Pin Functions
44 34
1
PQFP
11
12 22
Pin Function
1 P1.5
2 P1.6
3 P1.7
4 RST
5 P3.0/RxD
6 NIC*
7 P3.1/TxD
8 P3.2/INT0
9 P3.3/INT1
10 P3.4/T0
11 P3.5/T1
12 P3.6/WR
13 P3.7/RD
14 XTAL2
15 XTAL1
* NO INTERNAL CONNECTION
Pin Function
16 V
SS
17 NIC*
18 P2.0/A8
19 P2.1/A9
20 P2.2/A10
21 P2.3/A11
22 P2.4/A12
23 P2.5/A13
24 P2.6/A14
25 P2.7/A15
26 PSEN
27 ALE
28 NIC*
29 EA
/V
30 P0.7/AD7
PP
Pin Function
31 P0.6/AD6
32 P0.5/AD5
33 P0.4/AD4
34 P0.3/AD3
35 P0.2/AD2
36 P0.1/AD1
37 P0.0/AD0
38 V
39 NIC*
40 P1.0/T2
41 P1.1/T2EX
42 P1.2
43 P1.3
44 P1.4
33
23
CC
SU01064
1
2
3
4
5
6
7
8
9
DUAL
10
IN-LINE
PACKAGE
11
12
13
14
15
16
17
18
19
20
SS
1999 Oct 27
4
Philips Semiconductors Product specification
80C51 8-bit microcontroller family
4K/8K/16K/32K Flash
PIN DESCRIPTIONS
PIN NUMBER
MNEMONIC DIP LCC QFP TYPE NAME AND FUNCTION
V
SS
V
CC
P0.0–0.7 39–32 43–36 37–30 I/O Port 0: Port 0 is an open-drain, bidirectional I/O port. Port 0 pins that have 1s written to
P1.0–P1.7 1–8 2–9 40–44,
P2.0–P2.7 21–28 24–31 18–25 I/O Port 2: Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. Port 2 pins that have 1s
P3.0–P3.7 10–17 11,
RST 9 10 4 I Reset: A high on this pin for two machine cycles while the oscillator is running, resets the
ALE 30 33 27 O Address Latch Enable: Output pulse for latching the low byte of the address during an
PSEN 29 32 26 O Program Store Enable: The read strobe to external program memory. When executing
EA/V
PP
XTAL1 19 21 15 I Crystal 1: Input to the inverting oscillator amplifier and input to the internal clock
XTAL2 18 20 14 O Crystal 2: Output from the inverting oscillator amplifier.
NOTE: To avoid “latch-up” effect at power-on, the voltage on any pin (other than VPP) at any time must not be higher than VCC + 0.5 V or
– 0.5 V , respectively.
V
SS
20 22 16 I Ground: 0 V reference.
40 44 38 I Power Supply: This is the power supply voltage for normal, idle, and power-down operation.
them float and can be used as high-impedance inputs. Port 0 is also the multiplexed
low-order address and data bus during accesses to external program and data memory. In
this application, it uses strong internal pull-ups when emitting 1s.
1–3
1 2 40 I/O T2 (P1.0): Timer/Counter2 external count input/clockout (see Programmable Clock-Out).
2 3 41 I T2EX (P1.1): Timer/Counter2 reload/capture/direction control.
13–195,7–13
10 11 5 I RxD (P3.0): Serial input port
11 13 7 O TxD (P3.1): Serial output port
12 14 8 I INT0 (P3.2): External interrupt
13 15 9 I INT1 (P3.3): External interrupt
14 16 10 I T0 (P3.4): Timer 0 external input
15 17 11 I T1 (P3.5): Timer 1 external input
16 18 12 O WR (P3.6): External data memory write strobe
17 19 13 O RD (P3.7): External data memory read strobe
31 35 29 I External Access Enable/Programming Supply Voltage: EA must be externally held low
I/O Port 1: Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. Port 1 pins that have 1s
written to them are pulled high by the internal pull-ups and can be used as inputs. As inputs,
port 1 pins that are externally pulled low will source current because of the internal pull-ups.
(See DC Electrical Characteristics: I
written to them are pulled high by the internal pull-ups and can be used as inputs. As inputs,
port 2 pins that are externally being pulled low will source current because of the internal
pull-ups. (See DC Electrical Characteristics: I
during fetches from external program memory and during accesses to external data memory
that use 16-bit addresses (MOVX @DPTR). In this application, it uses strong internal
pull-ups when emitting 1s. During accesses to external data memory that use 8-bit addresses
(MOV @Ri), port 2 emits the contents of the P2 special function register.
I/O Port 3: Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. Port 3 pins that have 1s
written to them are pulled high by the internal pull-ups and can be used as inputs. As inputs,
port 3 pins that are externally being pulled low will source current because of the pull-ups.
(See DC Electrical Characteristics: I
89C51/89C52/89C54/89C58, as listed below:
device. An internal diffused resistor to V
capacitor to V
access to external memory. In normal operation, ALE is emitted at a constant rate of 1/6 the
oscillator frequency , and can be used for external timing or clocking. Note that one ALE
pulse is skipped during each access to external data memory. ALE can be disabled by
setting SFR auxiliary.0. With this bit set, ALE will be active only during a MOVX instruction.
code from the external program memory, PSEN
except that two PSEN
is not activated during fetches from internal program memory.
PSEN
to enable the device to fetch code from external program memory locations 0000H to the
maximum internal memory boundary. If EA
program memory unless the program counter contains an address greater than 0FFFH for
4 k devices, 1FFFH for 8 k devices, 3FFFH for 16 k devices, and 7FFFH for 32 k devices.
The value on the EA
have no effect. This pin also receives the 12.00 V programming supply voltage (V
FLASH programming.
generator circuits.
.
CC
activations are skipped during each access to external data memory.
pin is latched when RST is released and any subsequent changes
89C51/89C52/89C54/89C58
). Alternate function for Port 1:
IL
). Port 2 emits the high-order address byte
IL
). Port 3 also serves the special features of the
IL
permits a power-on reset using only an external
SS
is activated twice each machine cycle,
is held high, the device executes from internal
) during
PP
1999 Oct 27
5
Philips Semiconductors Product specification
80C51 8-bit microcontroller family
4K/8K/16K/32K Flash
Table 1. 89C51/89C52/89C54/89C58 Special Function Registers
SYMBOL DESCRIPTION
ACC* Accumulator E0H E7 E6 E5 E4 E3 E2 E1 E0 00H
AUXR# Auxiliary 8EH – – – – – – – AO xxxxxxx0B
AUXR1# Auxiliary 1 A2H – – – – GF2 0 – DPS xxxx00x0B
B* B register F0H F7 F6 F5 F4 F3 F2 F1 F0 00H
DPTR: Data Pointer (2 bytes)
DPH Data Pointer High 83H 00H
DPL Data Pointer Low 82H 00H
IE* Interrupt Enable A8H EA – ET2 ES ET1 EX1 ET0 EX0 0x000000B
IP* Interrupt Priority B8H – – PT2 PS PT1 PX1 PT0 PX0 xx000000B
IPH# Interrupt Priority High B7H – – PT2H PSH PT1H PX1H PT0H PX0H xx000000B
P0* Port 0 80H AD7 AD6 AD5 AD4 AD3 AD2 AD1 AD0 FFH
P1* Port 1 90H – – – – – – T2EX T2 FFH
P2* Port 2 A0H AD15 AD14 AD13 AD12 AD11 AD10 AD9 AD8 FFH
P3* Port 3 B0H RD WR T1 T0 INT1 INT0 TxD RxD FFH
DIRECT
ADDRESS
BIT ADDRESS, SYMBOL, OR ALTERNATIVE PORT FUNCTION
MSB LSB
AF AE AD AC AB AA A9 A8
BF BE BD BC BB BA B9 B8
B7 B6 B5 B4 B3 B2 B1 B0
87 86 85 84 83 82 81 80
97 96 95 94 93 92 91 90
A7 A6 A5 A4 A3 A2 A1 A0
B7 B6 B5 B4 B3 B2 B1 B0
89C51/89C52/89C54/89C58
RESET
VALUE
PCON#1Power Control 87H SMOD1 SMOD0 – POF
D7 D6 D5 D4 D3 D2 D1 D0
PSW* Program Status Word D0H CY AC F0 RS1 RS0 OV – P 000000x0B
RACAP2H# Timer 2 Capture High CBH 00H
RACAP2L# Timer 2 Capture Low CAH 00H
SADDR# Slave Address A9H 00H
SADEN# Slave Address Mask B9H 00H
SBUF Serial Data Buffer 99H xxxxxxxxB
9F 9E 9D 9C 9B 9A 99 98
SCON* Serial Control 98H
SP Stack Pointer 81H 07H
TCON* Timer Control 88H TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0 00H
T2CON* Timer 2 Control C8H TF2 EXF2 RCLK TCLK EXEN2 TR2 C/T2 CP/RL2 00H
T2MOD# Timer 2 Mode Control C9H – – – – – – T2OE DCEN xxxxxx00B
TH0 Timer High 0 8CH 00H
TH1 Timer High 1 8DH 00H
TH2# Timer High 2 CDH 00H
TL0 Timer Low 0 8AH 00H
TL1 Timer Low 1 8BH 00H
TL2# Timer Low 2 CCH 00H
TMOD T imer Mode 89H GATE C/T M1 M0 GATE C/T M1 M0 00H
* SFRs are bit addressable.
# SFRs are modified from or added to the 80C51 SFRs.
– Reserved bits.
1. Reset value depends on reset source.
2. Bit will not be affected by reset.
SM0/FE
8F 8E 8D 8C 8B 8A 89 88
CF CE CD CC CB CA C9 C8
SM1 SM2 REN TB8 RB8 TI RI 00H
2
GF1 GF0 PD IDL 00xxx000B
1999 Oct 27
6
Philips Semiconductors Product specification
80C51 8-bit microcontroller family
4K/8K/16K/32K Flash
FLASH EPROM MEMORY
General Description
The 89C51/89C52/89C54/89C58 FLASH reliably stores memory
contents even after 100 erase and program cycles. The cell is
designed to optimize the erase and programming mechanisms. In
addition, the combination of advanced tunnel oxide processing and
low internal electric fields for erase and programming operations
produces reliable cycling.
Features
•FLASH EPROM internal program memory with Chip Erase
•Up to 64 k byte external program memory if the internal program
memory is disabled (EA
•Programmable security bits
•100 minimum erase/program cycles for each byte
•10 year minimum data retention
•Programming support available from many popular vendors
= 0)
89C51/89C52/89C54/89C58
OSCILLA T OR CHARACTERISTICS
XTAL1 and XTAL2 are the input and output, respectively, of an
inverting amplifier. The pins can be configured for use as an
on-chip oscillator.
To drive the device from an external clock source, XTAL1 should be
driven while XTAL2 is left unconnected. There are no requirements
on the duty cycle of the external clock signal, because the input to
the internal clock circuitry is through a divide-by-two flip-flop.
However, minimum and maximum high and low times specified in
the data sheet must be observed.
RESET
A reset is accomplished by holding the RST pin high for at least two
machine cycles (24 oscillator periods), while the oscillator is running.
To insure a good power-on reset, the RST pin must be high long
enough to allow the oscillator time to start up (normally a few
milliseconds) plus two machine cycles. At power-on, the voltage on
V
and RST must come up at the same time for a proper start-up.
CC
Ports 1, 2, and 3 will asynchronously be driven to their reset
condition when a voltage above V
The value on the EA
no further effect.
pin is latched when RST is deasserted and has
(min.) is applied to RESET.
IH1
1999 Oct 27
7
Philips Semiconductors Product specification
80C51 8-bit microcontroller family
4K/8K/16K/32K Flash
LOW POWER MODES
Stop Clock Mode
The static design enables the clock speed to be reduced down to
0 MHz (stopped). When the oscillator is stopped, the RAM and
Special Function Registers retain their values. This mode allows
step-by-step utilization and permits reduced system power
consumption by lowering the clock frequency down to any value. For
lowest power consumption the Power Down mode is suggested.
Idle Mode
In the idle mode (see Table 2), the CPU puts itself to sleep while all
of the on-chip peripherals stay active. The instruction to invoke the
idle mode is the last instruction executed in the normal operating
mode before the idle mode is activated. The CPU contents, the
on-chip RAM, and all of the special function registers remain intact
during this mode. The idle mode can be terminated either by any
enabled interrupt (at which time the process is picked up at the
interrupt service routine and continued), or by a hardware reset
which starts the processor in the same manner as a power-on reset.
Power-Down Mode
To save even more power, a Power Down mode (see Table 2) can
be invoked by software. In this mode, the oscillator is stopped and
the instruction that invoked Power Down is the last instruction
executed. The on-chip RAM and Special Function Registers retain
their values down to 2.0 V and care must be taken to return V
the minimum specified operating voltages before the Power Down
Mode is terminated.
Either a hardware reset or external interrupt can be used to exit from
Power Down. Reset redefines all the SFRs but does not change the
on-chip RAM. An external interrupt allows both the SFRs and the
on-chip RAM to retain their values.
To properly terminate Power Down the reset or external interrupt
should not be executed before V
operating level and must be held active long enough for the
oscillator to restart and stabilize (normally less than 10ms).
With an external interrupt, INT0 and INT1 must be enabled and
configured as level-sensitive. Holding the pin low restarts the oscillator
but bringing the pin back high completes the exit. Once the interrupt
is serviced, the next instruction to be executed after RETI will be the
one following the instruction that put the device into Power Down.
is restored to its normal
CC
CC
to
89C51/89C52/89C54/89C58
Design Consideration
•When the idle mode is terminated by a hardware reset, the device
normally resumes program execution, from where it left off, up to
two machine cycles before the internal reset algorithm takes
control. On-chip hardware inhibits access to internal RAM in this
event, but access to the port pins is not inhibited. To eliminate the
possibility of an unexpected write when Idle is terminated by reset,
the instruction following the one that invokes Idle should not be
one that writes to a port pin or to external memory.
ONCE Mode
The ONCE (“On-Circuit Emulation”) Mode facilitates testing and
debugging of systems without the device having to be removed from
the circuit. The ONCE Mode is invoked by:
1. Pull ALE low while the device is in reset and PSEN
2. Hold ALE low as RST is deactivated.
While the device is in ONCE Mode, the Port 0 pins go into a float
state, and the other port pins and ALE and PSEN
high. The oscillator circuit remains active. While the device is in this
mode, an emulator or test CPU can be used to drive the circuit.
Normal operation is restored when a normal reset is applied.
Programmable Clock-Out
A 50% duty cycle clock can be programmed to come out on P1.0.
This pin, besides being a regular I/O pin, has two alternate
functions. It can be programmed:
1. to input the external clock for Timer/Counter 2, or
2. to output a 50% duty cycle clock ranging from 61Hz to 4MHz at a
16MHz operating frequency.
To configure the Timer/Counter 2 as a clock generator, bit C/T2 (in
T2CON) must be cleared and bit T20E in T2MOD must be set. Bit
TR2 (T2CON.2) also must be set to start the timer.
The Clock-Out frequency depends on the oscillator frequency and
the reload value of Timer 2 capture registers (RCAP2H, RCAP2L)
as shown in this equation:
Oscillator Frequency
4 (65536 * RCAP2H,RCAP2L)
Where (RCAP2H,RCAP2L) = the content of RCAP2H and RCAP2L
taken as a 16-bit unsigned integer.
In the Clock-Out mode Timer 2 roll-overs will not generate an
interrupt. This is similar to when it is used as a baud-rate generator.
It is possible to use Timer 2 as a baud-rate generator and a clock
generator simultaneously. Note, however, that the baud-rate and the
Clock-Out frequency will be the same.
is high;
are weakly pulled
Table 2. External Pin Status During Idle and Power-Down Mode
MODE PROGRAM MEMORY ALE PSEN PORT 0 PORT 1 PORT 2 PORT 3
Idle Internal 1 1 Data Data Data Data
Idle External 1 1 Float Data Address Data
Power-down Internal 0 0 Data Data Data Data
Power-down External 0 0 Float Data Data Data
1999 Oct 27
8
Philips Semiconductors Product specification
80C51 8-bit microcontroller family
4K/8K/16K/32K Flash
TIMER 2 OPERATION
Timer 2
Timer 2 is a 16-bit Timer/Counter which can operate as either an
event timer or an event counter, as selected by C/T
function register T2CON (see Figure 1). Timer 2 has three operating
modes: Capture, Auto-reload (up or down counting), and Baud Rate
Generator, which are selected by bits in the T2CON as shown in
Table 3.
Capture Mode
In the capture mode there are two options which are selected by bit
EXEN2 in T2CON. If EXEN2=0, then timer 2 is a 16-bit timer or
counter (as selected by C/T
sets bit TF2, the timer 2 overflow bit. This bit can be used to
generate an interrupt (by enabling the Timer 2 interrupt bit in the
IE register). If EXEN2= 1, Timer 2 operates as described above, but
with the added feature that a 1- to -0 transition at external input
T2EX causes the current value in the Timer 2 registers, TL2 and
TH2, to be captured into registers RCAP2L and RCAP2H,
respectively. In addition, the transition at T2EX causes bit EXF2 in
T2CON to be set, and EXF2 like TF2 can generate an interrupt
(which vectors to the same location as Timer 2 overflow interrupt.
The Timer 2 interrupt service routine can interrogate TF2 and EXF2
to determine which event caused the interrupt). The capture mode is
illustrated in Figure 2 (There is no reload value for TL2 and TH2 in
this mode. Even when a capture event occurs from T2EX, the
counter keeps on counting T2EX pin transitions or osc/12 pulses.).
2* in T2CON) which, upon overflowing
Auto-Reload Mode (Up or Down Counter)
In the 16-bit auto-reload mode, Timer 2 can be configured (as either
a timer or counter [C/T
or down. The counting direction is determined by bit DCEN (Down
Counter Enable) which is located in the T2MOD register (see
2* in T2CON]) then programmed to count up
2* in the special
89C51/89C52/89C54/89C58
Figure 3). When reset is applied the DCEN=0 which means Timer 2
will default to counting up. If DCEN bit is set, Timer 2 can count up
or down depending on the value of the T2EX pin.
Figure 4 shows Timer 2 which will count up automatically since
DCEN=0. In this mode there are two options selected by bit EXEN2
in T2CON register. If EXEN2=0, then T imer 2 counts up to 0FFFFH
and sets the TF2 (Overflow Flag) bit upon overflow. This causes the
Timer 2 registers to be reloaded with the 16-bit value in RCAP2L
and RCAP2H. The values in RCAP2L and RCAP2H are preset by
software means.
If EXEN2=1, then a 16-bit reload can be triggered either by an
overflow or by a 1-to-0 transition at input T2EX. This transition also
sets the EXF2 bit. The Timer 2 interrupt, if enabled, can be
generated when either TF2 or EXF2 are 1.
In Figure 5 DCEN=1 which enables Timer 2 to count up or down.
This mode allows pin T2EX to control the direction of count. When a
logic 1 is applied at pin T2EX Timer 2 will count up. Timer 2 will
overflow at 0FFFFH and set the TF2 flag, which can then generate
an interrupt, if the interrupt is enabled. This timer overflow also
causes the 16–bit value in RCAP2L and RCAP2H to be reloaded
into the timer registers TL2 and TH2.
When a logic 0 is applied at pin T2EX this causes Timer 2 to count
down. The timer will underflow when TL2 and TH2 become equal to
the value stored in RCAP2L and RCAP2H. Timer 2 underflow sets
the TF2 flag and causes 0FFFFH to be reloaded into the timer
registers TL2 and TH2.
The external flag EXF2 toggles when Timer 2 underflows or
overflows. This EXF2 bit can be used as a 17th bit of resolution if
needed. The EXF2 flag does not generate an interrupt in this mode
of operation.
(MSB) (LSB)
TF2 EXF2 RCLK TCLK EXEN2 TR2 C/T2
Symbol Position Name and Significance
TF2 T2CON.7 Timer 2 overflow flag set by a T imer 2 overflow and must be cleared by software. TF2 will not be set
EXF2 T2CON.6 Timer 2 external flag set when either a capture or reload is caused by a negative transition on T2EX and
RCLK T2CON.5 Receive clock flag. When set, causes the serial port to use Timer 2 overflow pulses for its receive clock
TCLK T2CON.4 Transmit clock flag. When set, causes the serial port to use Timer 2 overflow pulses for its transmit clock
EXEN2 T2CON.3 Timer 2 external enable flag. When set, allows a capture or reload to occur as a result of a negative
TR2 T2CON.2 Start/stop control for Timer 2. A logic 1 starts the timer.
C/T2
CP/RL2
T2CON.1 Timer or counter select. (Timer 2)
T2CON.0 Capture/Reload flag. When set, captures will occur on negative transitions at T2EX if EXEN2 = 1. When
when either RCLK or TCLK = 1.
EXEN2 = 1. When Timer 2 interrupt is enabled, EXF2 = 1 will cause the CPU to vector to the Timer 2
interrupt routine. EXF2 must be cleared by software. EXF2 does not cause an interrupt in up/down
counter mode (DCEN = 1).
in modes 1 and 3. RCLK = 0 causes Timer 1 overflow to be used for the receive clock.
in modes 1 and 3. TCLK = 0 causes Timer 1 overflows to be used for the transmit clock.
transition on T2EX if Timer 2 is not being used to clock the serial port. EXEN2 = 0 causes Timer 2 to
ignore events at T2EX.
0 = Internal timer (OSC/12)
1 = External event counter (falling edge triggered).
cleared, auto-reloads will occur either with Timer 2 overflows or negative transitions at T2EX when
EXEN2 = 1. When either RCLK = 1 or TCLK = 1, this bit is ignored and the timer is forced to auto-reload
on Timer 2 overflow .
Figure 1. Timer/Counter 2 (T2CON) Control Register
CP/RL2
SU00728
1999 Oct 27
9
Philips Semiconductors Product specification
80C51 8-bit microcontroller family
4K/8K/16K/32K Flash
Table 3. Timer 2 Operating Modes
RCLK + TCLK CP/RL2 TR2 MODE
0 0 1 16-bit Auto-reload
0 1 1 16-bit Capture
1 X 1 Baud rate generator
X X 0 (off)
OSC
T2 Pin
÷ 12
Transition
Detector
C/T2
C/T2
= 0
= 1
TR2
Control
Capture
TL2
(8-bits)
RCAP2L RCAP2H
89C51/89C52/89C54/89C58
TH2
(8-bits)
TF2
Timer 2
Interrupt
T2EX Pin
Control
EXEN2
EXF2
SU00066
Figure 2. Timer 2 in Capture Mode
T2MOD Address = 0C9H Reset Value = XXXX XX00B
Not Bit Addressable
— — — — — — T2OE DCEN
Bit
76543210
Symbol Function
— Not implemented, reserved for future use.*
T2OE Timer 2 Output Enable bit.
DCEN Down Count Enable bit. When set, this allows Timer 2 to be configured as an up/down counter.
* User software should not write 1s to reserved bits. These bits may be used in future 8051 family products to invoke new features.
In that case, the reset or inactive value of the new bit will be 0, and its active value will be 1. The value read from a reserved bit is
indeterminate.
SU00729
Figure 3. Timer 2 Mode (T2MOD) Control Register
1999 Oct 27
10
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