Intel 8XC251SA, Руководство пользователя

Страница: 146 / 458

8XC251SA, SB, SP, SQ USER’S MANUAL
8-12
8.6.2 Auto-reload Mode
The auto-reload mode configures timer 2 as a 16-bit timer or event counter with automatic reload.
The timer operates an as an up counter or as an up/down counter, as determined by the down
counter enable bit (DCEN). At device reset, DCEN is cleared, so in the auto-reload mode, timer
2 defaults to operation as an up counter.
8.6.2.1 Up Counter Operation
When DCEN = 0, timer 2 operates as an up counter (Figure 8-8). The external enable bit EXEN2
in the T2CON register provides two options (Figure 8-12). If EXEN2 = 0, timer 2 counts up to
FFFFH and sets the TF2 overflow flag. The overflow condition loads the 16-bit value in the re-
load/capture registers (RCAP2H, RCAP2L) into the timer registers (TH2, TL2). The values in
RCAP2H and RCAP2L are preset by software.
If EXEN2 = 1, the timer registers are reloaded by either a timer overflow or a high-to-low tran-
sition at external input T2EX. This transition also sets the EXF2 bit in the T2CON register. Either
TF2 or EXF2 bit can generate a timer 2 interrupt request.
Figure 8-8. Timer 2: Auto Reload Mode (DCEN = 0)
Interrupt
Request
T2EX
TF2
12
T2
Overflow
TR2
TH2
(8 Bits)
TL2
(8 Bits)
EXEN2
EXF2
Reload
A4115-02
XTAL1
RCAP2H RCAP2L
C/T2#
0
1