SM89516B datasheet(31/49 Pages) SYNCMOS

31 / 49 page

SM89516B

8-Bit Micro-controller

64KB Flash

& 1KB RAM embedded

Specifications subject to change without notice contact your sales representatives for the most recent information.

ISSFD-M087

Ver D SM89516B 08/07/2015

- 31 -

7.2

Auto-reload (Up or Down Counter)

Timer 2 can be programmed to count up or down when configured in its 16-bit auto-reload mode. This feature is

invoked by a bit named DCEN (Down Counter Enable) located in the SFR T2MOD. Upon reset, the DCEN bit is set

to 0 so that Timer 2 will default to count up. When DCEN is set, Timer 2 can count up or down depending on the

value of the T2EX pin.

Fig. 7-2 shows Timer 2 automatically counting up when DCEN = 0. In this mode there are two options selected by

bit EXEN2 in T2CON. If EXEN2 = 0, Timer 2 counts up to FFFFh 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 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 Fig. 7-3. In this mode the T2EX pin controls

the direction of count. A logic 1 at T2EX makes Timer 2 count up. The timer will overflow at FFFFh 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. Now the timer underflows when TH2 and TL2 are equal to the values

stored in RCAP2H and RCAP2L. The underflow sets the TF2 bit and causes FFFFH to be reloaded into the timer

registers.

The EXF2 bit toggles whenever Timer 2 overflows or underflows. This bit can be used as a 17th bit of resolution if

desired. In this operating mode, EXF2 does not flag an interrupt.

C/T2=0

C/T2=1

T2 pin

TL2

(8 BITS)

TH2

(8 BITS)

TF2

Fosc/12

TR2

RCAP2L RCAP2H

T2 EX pin

EXEN2

EXF2

Transition

Detector

Timer2 Interrupt

Timier2 in Auto Reload Mode

(DCEN=0)

RELOAD

Fig. 7-2：Timer 2 in auto reload mode (DCEN=0)

SM89516B Datasheet(PDF) 31 Page - SyncMOS Technologies,Inc

SM89516B Datasheet(HTML) 31 Page - SyncMOS Technologies,Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49

Datasheet Download

Link URL