AT89C52-12AA ATMEL [ATMEL Corporation], AT89C52-12AA Datasheet - Page 7

• Manufacturer Part Number: AT89C52-12AA
• Description: 8-Bit Microcontroller with 8K Bytes Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Figure 2 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 over-
flow 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 soft-
ware. 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 generate 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
Figure 2. Timer 2 Auto Reload Mode (DCEN = 0)
Table 4. T2MOD—Timer 2 Mode Control Register
Symbol
—
T2OE
DCEN
T2EX PIN
T2MOD Address = 0C9H
Not Bit Addressable
Bit
OSC
T2 PIN
—
7
Function
Not implemented, reserved for future
Timer 2 Output Enable bit.
When set, this bit allows Timer 2 to be configured as an up/down counter.
÷12
TRANSITION
DETECTOR
—
6
C/T2 = 0
C/T2 = 1
—
5
EXEN2
TR2
—
4
CONTROL
CONTROL
RELOAD
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 regis-
ters, 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.
—
3
RCAP2H
TH2
—
2
RCAP2L
TL2
Reset Value = XXXX XX00B
T2OE
1
OVERFLOW
EXF2
TF2
DCEN
0
INTERRUPT
TIMER 2
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