SM59D03G2 Datasheet, PDF (27/67 Pages) SyncMOS Technologies,Inc – 8-Bits Micro-controller

SM59D03G2
8-Bits Micro-controller
8KB+ ISP Flash & 1KB RAM embedded
Figure 7-1： Timer 2 in capture mode
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.
Figure 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 Figure 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.
Specifications subject to change without notice contact your sales representatives for the most recent information.
ISSFD-M030
27
Ver.C SM59D03G2 07/2009