AT89C51RC-33AC ATMEL Corporation, AT89C51RC-33AC Datasheet - Page 13

• Manufacturer Part Number: AT89C51RC-33AC
• Description: 8-bit Microcontroller with 32K Bytes Flash
• Manufacturer: ATMEL Corporation

Figure 2. Timer in Capture Mode
1920B–MICRO–11/02
T2EX PIN
OSC
T2 PIN
÷12
TRANSITION
DETECTOR
Figure 3 shows Timer 2 automatically counting up when DCEN=0. In this mode, two
options are selected by bit EXEN2 in T2CON. If EXEN2 = 0, Timer 2 counts up to
0FFFFH and then sets the TF2 bit upon overflow. The overflow also causes the timer
registers to be reloaded with the 16-bit value in RCAP2H and RCAP2L. The values in
Timer in Capture ModeRCAP2H and RCAP2L are preset by software. If EXEN2 = 1, a
16-bit reload can be triggered either by an overflow or by a 1-to-0 transition at external
input T2EX. This transition also sets the EXF2 bit. Both the TF2 and EXF2 bits can gen-
erate an interrupt if enabled.
Setting the DCEN bit enables Timer 2 to count up or down, as shown in Figure 3. In this
mode, the T2EX pin controls the direction of the count. A logic 1 at T2EX makes Timer 2
count up. The timer will overflow at 0FFFFH and set the TF2 bit. This overflow also
causes the 16-bit value in RCAP2H and RCAP2L to be reloaded into the timer registers,
TH2 and TL2, respectively.
A logic 0 at T2EX makes Timer 2 count down. The timer underflows when TH2 and TL2
equal the values stored in RCAP2H and RCAP2L. The underflow sets the TF2 bit and
causes 0FFFFH to be reloaded into the timer registers.
The EXF2 bit toggles whenever Timer 2 overflows or underflows and can be used as a
17th bit of resolution. In this operating mode, EXF2 does not flag an interrupt.
C/T2 = 0
C/T2 = 1
EXEN2
TR2
CAPTURE
CONTROL
CONTROL
RCAP2H
TH2
EXF2
RCAP2L
TL2
OVERFLOW
TF2
AT89C51RC
INTERRUPT
TIMER 2
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