Figure 2. Timer 2 Auto Reload Mode (DCEN = 0)

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

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

Table 4. T2MOD—Timer 2 Mode Control Register

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

overflow also causes the timer registers to be reloaded

with the 16 bit value in RCAP2H and RCAP2L. The values

in RCAP2H and RCAP2L are preset by software. If

EXEN2 = 1, a 16 bit reload can be triggered either by an

overflow or by a l-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

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 regis-

ters.

The EXF2 bit toggles whenever Timer 2 overflows or un-

derflows and can be used as a 17th bit of resolution. In this

operating mode, EXF2 does not flag an interrupt.

Auto-Reload (Up or Down Counter) (Continued)

AT48801

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