AP160

Version 0.0

9

AMIC Technology, Inc.

In this mode, two options are selected by bit EXEN2 in T2CON. If EXEN2=0, Timer2 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 Mode RCAP2H 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 generate an interrupt if enabled. Setting the DCEN bit

enables Timer2 to count up or down, as shown in Figure 3. In the 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. The 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

RACP2L. 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 17

not flag an interrupt.

Table 3. T2MOD (Timer 2 Mode Control Register)

T2Mod Address = 0C9H

Reset Value = XXXX XX00B

Not bit addressable

Bit

7

6

5

4

3

2

1

0

Symbol

-

-

-

-

-

-

T2OE

DCEN

Symbol

Function

-

Not implemented, reserved for future

T2OE

Timer 2 Output Enable bit.

DCEN

When set, this bit allows Timer 2 to be configured as an up/down counter.

OSC

C/T2=0

T2 PIN

CONTROL

C/T2=1

T2EX PIN

TR2

12

÷

OVERFLOW

0FFH

0FFH

RCAP2H

RCAP2L

TH2

TL2

TF2

(DOWN COUNTING RELOAD VALUE)

COUNT

DIRECTION

1=UP

0=DOWN

TIMER 2

INTERRUPT

EXF2

TOGGLE

(UP COUNTING RELOAD VALUE)

Figure 3. Timer 2 Auto Reload Mode (DCEN=1)