4K/8K/16K/32K ROM/OTP
128B/256B RAM
low voltage (2.7 to 5.5 V), low power, high speed (30/33 MHz)
Preliminary data2001 Sep 24
Philips SemiconductorsPreliminary data
80C51 8-bit microcontroller family
4K/8K/16K/32K ROM/OTP, low voltage (2.7 to 5.5 V),
low power, high speed (30/33 MHz)
DESCRIPTION
The Philips microcontrollers described in this data sheet are
high-performance static 80C51 designs incorporating Philips’
high-density CMOS technology with operation from 2.7 V to 5.5 V .
They support both 6-clock and 12-clock operation.
The 8xC31X2/51X2 and 8xC32X2/52X2/54X2/58X2 contain
128 byte RAM and 256 byte RAM respectively, 32 I/O lines, three
16-bit counter/timers, a six-source, four-priority level nested interrupt
structure, a serial I/O port for either multi-processor
communications, I/O expansion or full duplex UART, and on-chip
oscillator and clock circuits.
selectable modes of power reduction — idle mode and power-down
mode — are available. The idle mode freezes the CPU while
allowing the RAM, timers, serial port, and interrupt system to
continue functioning. The power-down mode saves the RAM
contents but freezes the oscillator, causing all other chip functions to
be inoperative. Since the design is static, the clock can be stopped
without loss of user data. Then the execution can be resumed from
the point the clock was stopped.
SELECTION TABLE
For applications requiring more ROM and RAM, as well as more
on-chip peripherals, see the P89C66x and P89C51Rx2 data sheets.
80C3xX2; 80C5xX2;
87C5xX2
In addition, the devices are low power static designs which offer a
wide range of operating frequencies down to zero. Two software
4K/8K/16K/32K ROM/OTP, low voltage (2.7 to 5.5 V),
low power, high speed (30/33 MHz)
80C3xX2; 80C5xX2;
87C5xX2
PIN DESCRIPTIONS
PIN NUMBER
MNEMONICDIPPLCC LQFP TYPE NAME AND FUNCTION
V
SS
V
CC
P0.0-0.739–32 43–36 37–30I/OPort 0: Port 0 is an open-drain, bidirectional I/O port. Port 0 pins that have 1s written to
P1.0–P1.71–82–940–44,
P2.0–P2.721–28 24–31 18–25I/OPort 2: Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. Port 2 pins that have 1s
P3.0–P3.710–1711,
RST9104IReset: A high on this pin for two machine cycles while the oscillator is running, resets the
ALE/PROG303327OAddress Latch Enable/Program Pulse: Output pulse for latching the low byte of the
PSEN293226OProgram Store Enable: The read strobe to external program memory. When the device is
EA/V
PP
XTAL1192115ICrystal 1: Input to the inverting oscillator amplifier and input to the internal clock generator
XTAL2182014OCrystal 2: Output from the inverting oscillator amplifier.
NOTE:
To avoid “latch-up” effect at power-on, the voltage on any pin at any time must not be higher than V
202216IGround: 0 V reference.
404438IPower 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. Port 0 also outputs the
code bytes during program verification and received code bytes during EPROM
programming. External pull-ups are required during program verification.
1–3
1240I/OT2 (P1.0): Timer/Counter 2 external count input/clockout (see Programmable Clock-Out)
2341IT2EX (P1.1): Timer/Counter 2 Reload/Capture/Direction control
13–195,7–13
10115IRxD (P3.0): Serial input port
11137OTxD (P3.1): Serial output port
12148IINT0 (P3.2): External interrupt
13159IINT1 (P3.3): External interrupt
141610IT0 (P3.4): Timer 0 external input
151711IT1 (P3.5): Timer 1 external input
161812OWR (P3.6): External data memory write strobe
171913ORD (P3.7): External data memory read strobe
313529IExternal Access Enable/Programming Supply Voltage: EA must be externally held low to enable the device
I/OPort 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
during program memory verification. Alternate functions for Port 1 include:
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: IIL). Port 2 emits the high-order address byte
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. Some Port 2 pins
receive the high order address bits during EPROM programming and verification.
I/OPort 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: IIL). Port 3 also serves the special features of the 80C51
family, as listed below:
device. An internal diffused resistor to VSS permits a power-on reset using only an external
capacitor to VCC.
address during an access to external memory. In normal operation, ALE is emitted at a
constant rate of 1/6 (12X Mode) or 1/3 (6X Mode) 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. This pin is also the program pulse input (PROG
programming. ALE can be disabled by setting SFR auxiliary.0. With this bit set, ALE will be
active only during a MOVX instruction.
executing code from the external program memory, PSEN is activated twice each machine
cycle, except that two PSEN activations are skipped during each access to external data
memory. PSEN is not activated during fetches from internal program memory.
to fetch code from external program memory locations 0000H to 0FFFH/1FFFH/3FFFH/7FFFH. If EA is held
high, the device executes from internal program memory unless the program counter contains an address
greater than the on-chip ROM/OTP. This pin also receives the 12.75 V programming supply voltage (VPP) during
EPROM programming. If security bit 1 is programmed, EA will be internally latched on Reset.
circuits.
). Port 1 also receives the low-order address byte
IL
) during EPROM
+ 0.5 V or VSS – 0.5 V, respectively.
CC
2001 Sep 24
9
Philips SemiconductorsPreliminary data
80C51 8-bit microcontroller family
4K/8K/16K/32K ROM/OTP, low voltage (2.7 to 5.5 V),
low power, high speed (30/33 MHz)
TH0Timer High 08CH00H
TH1Timer High 18DH00H
TH2#Timer High 2CDH00H
TL0Timer Low 08AH00H
TL1Timer Low 18BH00H
TL2#Timer Low 2CCH00H
TMODTimer Mode89HGATEC/TM1M0GATEC/TM1M000H
NOTE:
Unused register bits that are not defined should not be set by the user’s program. If violated, the device could function incorrectly.
* SFRs are bit addressable.
# SFRs are modified from or added to the 80C51 SFRs.
– Reserved bits.
1. Reset value depends on reset source.
2. LPEP – Low Power EPROM operation (OTP only)
SM0/FE
8F8E8D8C8B8A8988
CFCECDCCCBCAC9C8
SM1SM2RENTB8RB8TIRI00H
2001 Sep 24
10
Philips SemiconductorsPreliminary data
80C51 8-bit microcontroller family
4K/8K/16K/32K ROM/OTP, low voltage (2.7 to 5.5 V),
low power, high speed (30/33 MHz)
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, as shown in the logic symbol.
To drive the device from an external clock source, XTAL1 should be
driven while XTAL2 is left unconnected. 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 in 12-clock and 12
oscillator periods in 6-clock mode), while the oscillator is running. To
insure a reliable power-up 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. After the reset, the part runs
in 12-clock mode.
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 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 VCC to
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
80C3xX2; 80C5xX2;
87C5xX2
on-chip RAM. An external interrupt allows both the SFRs and the
on-chip RAM to retain their values. WUPD (AUXR1.3–Wakeup from
Power Down) enables or disables the wakeup from power down with
external interrupt. Where:
WUPD = 0: Disable
WUPD = 1: Enable
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 10 ms).
To terminate Power Down with an external interrupt, INT0
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.
Low-Power EPROM operation (LPEP)
The EPROM array contains some analog circuits that are not
required when V
greater than 4 V . The LPEP bit (AUXR.4), when set, will powerdown
these analog circuits resulting in a reduced supply current. This bit
should be set ONLY for applications that operate at a V
4 V.
is less than 4 V, but are required for a V
CC
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 in the following way:
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.
is restored to its normal
CC
are weakly pulled
or INT1
CC
less than
CC
is high;
Table 2. External Pin Status During Idle and Power-Down Modes
4K/8K/16K/32K ROM/OTP, low voltage (2.7 to 5.5 V),
low power, high speed (30/33 MHz)
Clock Control Register (CKCON)
This device provides control of the 6-clock/12-clock mode by an
SFR bit (bit X2 in register CKCON). When this bit is set to 0,
12-clock mode is activated. By setting this bit to 1, the system is
switching to 6-clock mode. Having this option implemented as SFR
bit, it can be accessed anytime and changed to either value. An
important thing to have in mind is that changing X2 from 0 to 1 will
result in executing user code at twice the speed, since all system
time intervals will be divided by 2. Changing from 6-clock to 12-clock
mode will slow down running code by a factor of 2.
Programmable Clock-Out
A 50% duty cycle clock can be programmed to be output 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 61 Hz to 4 MHz at
a 16 MHz operating frequency.
To configure the Timer/Counter 2 as a clock generator , bit C/T
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.
TIMER 0 AND TIMER 1 OPERATION
Timer 0 and Timer 1
The “Timer” or “Counter” function is selected by control bits C/T in
the Special Function Register TMOD. These two Timer/Counters
have four operating modes, which are selected by bit-pairs (M1, M0)
in TMOD. Modes 0, 1, and 2 are the same for both Timers/Counters.
Mode 3 is different. The four operating modes are described in the
following text.
2 (in
80C3xX2; 80C5xX2;
87C5xX2
Mode 0
Putting either Timer into Mode 0 makes it look like an 8048 T imer,
which is an 8-bit Counter with a divide-by-32 prescaler. Figure 2
shows the Mode 0 operation.
In this mode, the Timer register is configured as a 13-bit register . As
the count rolls over from all 1s to all 0s, it sets the Timer interrupt
flag TFn. The counted input is enabled to the Timer when TRn = 1
and either GA TE = 0 or INTn
Timer to be controlled by external input INTn
measurements). TRn is a control bit in the Special Function Register
TCON (Figure 3).
The 13-bit register consists of all 8 bits of THn and the lower 5 bits
of TLn. The upper 3 bits of TLn are indeterminate and should be
ignored. Setting the run flag (TRn) does not clear the registers.
Mode 0 operation is the same for Timer 0 as for Timer 1. There are
two different GA TE bits, one for Timer 1 (TMOD.7) and one for Timer
0 (TMOD.3).
Mode 1
Mode 1 is the same as Mode 0, except that the Timer register is
being run with all 16 bits.
Mode 2
Mode 2 configures the Timer register as an 8-bit Counter (TLn) with
automatic reload, as shown in Figure 4. Overflow from TLn not only
sets TFn, but also reloads TLn with the contents of THn, which is
preset by software. The reload leaves THn unchanged.
Mode 2 operation is the same for Timer 0 as for Timer 1.
Mode 3
Timer 1 in Mode 3 simply holds its count. The effect is the same as
setting TR1 = 0.
Timer 0 in Mode 3 establishes TL0 and TH0 as two separate
counters. The logic for Mode 3 on Timer 0 is shown in Figure 5. TL0
uses the Timer 0 control bits: C/T
pin INT0
cycles) and takes over the use of TR1 and TF1 from Timer 1. Thus,
TH0 now controls the “Timer 1” interrupt.
Mode 3 is provided for applications requiring an extra 8-bit timer on
the counter. With Timer 0 in Mode 3, an 80C51 can look like it has
three Timer/Counters. When Timer 0 is in Mode 3, Timer 1 can be
turned on and off by switching it out of and into its own Mode 3, or
can still be used by the serial port as a baud rate generator, or in
fact, in any application not requiring an interrupt.
. TH0 is locked into a timer function (counting machine
= 1. (Setting GATE = 1 allows the
, to facilitate pulse width
, GATE, TR0, and TF0 as well as
2001 Sep 24
12
Philips SemiconductorsPreliminary data
80C51 8-bit microcontroller family
80C3xX2; 80C5xX2;
4K/8K/16K/32K ROM/OTP, low voltage (2.7 to 5.5 V),
low power, high speed (30/33 MHz)
TMODAddress = 89HReset Value = 00H
Not Bit Addressable
76543 2 1 0
GATEC/TM1
TIMER 1TIMER 0
BITSYMBOLFUNCTION
TMOD.3/GA TEGating control when set. Timer/Counter “n” is enabled only while “INTn
TMOD.7“TRn” control pin is set. when cleared Timer “n” is enabled whenever “TRn” control bit is set.
TMOD.2/C/T
Timer or Counter Selector cleared for Timer operation (input from internal system clock.)
TMOD.6Set for Counter operation (input from “Tn” input pin).
M1 M0OPERATING
008048 Timer: “TLn” serves as 5-bit prescaler.
0116-bit Timer/Counter: “THn” and “TLn” are cascaded; there is no prescaler.
108-bit auto-reload Timer/Counter: “THn” holds a value which is to be reloaded
into “TLn” each time it overflows.
11(Timer 0) TL0 is an 8-bit Timer/Counter controlled by the standard T imer 0 control bits.
TH0 is an 8-bit timer only controlled by Timer 1 control bits.
11(Timer 1) Timer/Counter 1 stopped.
M0GATEC/T
M1M0
” pin is high and
SU01580
87C5xX2
OSC
Timer n
Gate bit
INTn Pin
÷ 12
÷ 6
Tn Pin
TRn
Figure 1. Timer/Counter 0/1 Mode Control (TMOD) Register
4K/8K/16K/32K ROM/OTP, low voltage (2.7 to 5.5 V),
low power, high speed (30/33 MHz)
TCONAddress = 88HReset Value = 00H
Bit Addressable
76543210
IE0IT1IE1TR0TF0TR1TF1
BITSYMBOLFUNCTION
TCON.7TF1Timer 1 overflow flag. Set by hardware on Timer/Counter overflow.
Cleared by hardware when processor vectors to interrupt routine, or clearing the bit in software.
TCON.6TR1Timer 1 Run control bit. Set/cleared by software to turn T imer/Counter on/off.
TCON.5TF0Timer 0 overflow flag. Set by hardware on Timer/Counter overflow.
Cleared by hardware when processor vectors to interrupt routine, or by clearing the bit in software.
TCON.4TR0Timer 0 Run control bit. Set/cleared by software to turn T imer/Counter on/off.
TCON.3IE1Interrupt 1 Edge flag. Set by hardware when external interrupt edge detected.
Cleared when interrupt processed.
TCON.2IT1Interrupt 1 type control bit. Set/cleared by software to specify falling edge/low level triggered
external interrupts.
TCON.1IE0Interrupt 0 Edge flag. Set by hardware when external interrupt edge detected.
Cleared when interrupt processed.
TCON.0IT0Interrupt 0 Type control bit. Set/cleared by software to specify falling edge/low level
triggered external interrupts.
IT0
87C5xX2
SU01516
OSC
Timer n
Gate bit
INTn Pin
÷ 12
÷ 6
Tn Pin
TRn
Figure 3. Timer/Counter 0/1 Control (TCON) Register
4K/8K/16K/32K ROM/OTP, low voltage (2.7 to 5.5 V),
low power, high speed (30/33 MHz)
OSC
Timer 0
Gate bit
INT0 Pin
OSC
÷ 12
÷ 6
T0 Pin
÷ 12
TR0
X2 = 0
X2 = 1
X2 = 0
C/T = 0
= 1
C/T
Control
TL0
(8 Bits)
80C3xX2; 80C5xX2;
87C5xX2
TF0
Interrupt
÷ 6
X2 = 1
TR1
Figure 5. Timer/Counter 0 Mode 3: Two 8-Bit Counters
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
2 in the special
function register T2CON (see Figure 6). 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 7 (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 (12-clock Mode) or osc/6
(6-clock Mode) pulses).
2 in T2CON) which, upon overflowing,
Control
TH0
(8 Bits)
TF1
Interrupt
SU01525
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
Figure 8). After reset, DCEN=0 which means Timer 2 will default to
counting up. If DCEN is set, Timer 2 can count up or down
depending on the value of the T2EX pin.
Figure 9 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.
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 10 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.
2 in T2CON), then programmed to count up
2001 Sep 24
15
Philips SemiconductorsPreliminary data
80C51 8-bit microcontroller family
80C3xX2; 80C5xX2;
4K/8K/16K/32K ROM/OTP, low voltage (2.7 to 5.5 V),
low power, high speed (30/33 MHz)
A logic 0 applied to pin T2EX causes Timer 2 to count down. The
timer will underflow when TL2 and TH2 become equal to the value
stored in RCAP2L and RCAP2H. A 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.
TF2T2CON.7Timer 2 overflow flag set by a Timer 2 overflow and must be cleared by software. TF2 will not be set
EXF2T2CON.6Timer 2 external flag set when either a capture or reload is caused by a negative transition on T2EX and
RCLKT2CON.5Receive clock flag. When set, causes the serial port to use Timer 2 overflow pulses for its receive clock
TCLKT2CON.4Transmit clock flag. When set, causes the serial port to use Timer 2 overflow pulses for its transmit clock
EXEN2T2CON.3Timer 2 external enable flag. When set, allows a capture or reload to occur as a result of a negative
TR2T2CON.2Start/stop control for Timer 2. A logic 1 starts the timer.
C/T
2T2CON.1Timer or counter select. (Timer 2)
2T2CON.0Capture/Reload flag. When set, captures will occur on negative transitions at T2EX if EXEN2 = 1. When
CP/RL
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 or OSC/6, depending on mode)
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 6. Timer/Counter 2 (T2CON) Control Register
2CP/RL2
SU01518
2001 Sep 24
16
Philips SemiconductorsPreliminary data
80C51 8-bit microcontroller family
4K/8K/16K/32K ROM/OTP, low voltage (2.7 to 5.5 V),
low power, high speed (30/33 MHz)
OSC
T2EX Pin
÷ 12
÷ 6
T2 Pin
Transition
Detector
X2 = 0
X2 = 1
C/T2 = 0
2 = 1
C/T
Control
TR2
Control
Capture
TL2
(8-bits)
RCAP2LRCAP2H
TH2
(8-bits)
80C3xX2; 80C5xX2;
87C5xX2
TF2
Timer 2
Interrupt
EXF2
EXEN2
SU01496
Figure 7. Timer 2 in Capture Mode
T2MODAddress = 0C9HReset Value = XXXX XX00B
Not Bit Addressable
76543210
——————T2OEDCEN
SymbolPositionFunction
—Not implemented, reserved for future use.*
T2OET2MOD.1Timer 2 Output Enable bit.
DCENT2MOD.0Down 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.
SU01519
Figure 8. Timer 2 Mode (T2MOD) Control Register
2001 Sep 24
17
Philips SemiconductorsPreliminary data
80C51 8-bit microcontroller family
4K/8K/16K/32K ROM/OTP, low voltage (2.7 to 5.5 V),
low power, high speed (30/33 MHz)
OSC
T2EX PIN
÷ 12
÷ 6
T2 Pin
X2 = 0
X2 = 1
TRANSITION
DETECTOR
C/T2 = 0
2 = 1
C/T
EXEN2
CONTROL
TR2
CONTROL
RELOAD
TL2
(8-BITS)
RCAP2LRCAP2H
TH2
(8-BITS)
80C3xX2; 80C5xX2;
87C5xX2
TF2
TIMER 2
INTERRUPT
EXF2
SU01497
OSC
÷ 12
÷ 6
T2 Pin
X2 = 0
X2 = 1
Figure 9. Timer 2 in Auto-Reload Mode (DCEN = 0)
(DOWN COUNTING RELOAD VALUE)
FFHFFH
C/T2 = 0
TL2TH2
2 = 1
C/T
CONTROL
TR2
RCAP2LRCAP2H
(UP COUNTING RELOAD VALUE)T2EX PIN
Figure 10. Timer 2 Auto Reload Mode (DCEN = 1)
OVERFLOW
TOGGLE
COUNT
DIRECTION
1 = UP
0 = DOWN
TF2
EXF2
INTERRUPT
SU01498
2001 Sep 24
18
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