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9.4.4
Operation
Timer F is a 16-bit counter that increments on each input clock pulse. The timer F value is
constantly compared with the value set in output compare register F, and the counter can be
cleared, an interrupt requested, or port output toggled, when the two values match. Timer F can
also function as two independent 8-bit timers.
1. Timer F operation
Timer F has two operating modes, 16-bit timer mode and 8-bit timer mode. The operation in each
of these modes is described below.
a. Operation in 16-bit timer mode
When CKSH2 is cleared to 0 in timer control register F (TCRF), timer F operates as a 16-bit
timer.
Following a reset, timer counter F (TCF) is initialized to H'0000, output compare register F
(OCRF) to H'FFFF, and timer control register F (TCRF) and timer control/status register F
(TCSRF) to H'00. The counter starts incrementing on external event (TMIF) input. The
external event edge selection is set by IEG3 in the IRQ edge select register (IEGR).
The timer F operating clock can be selected from four internal clocks output by prescaler S or
an external clock by means of bits CKSL2 to CKSL0 in TCRF.
OCRF contents are constantly compared with TCF, and when both values match, CMFH is set
to 1 in TCSRF. If IENTFH in IENR2 is 1 at this time, an interrupt request is sent to the CPU,
and at the same time, TMOFH pin output is toggled. If CCLRH in TCSRF is 1, TCF is
cleared. TMOFH pin output can also be set by TOLH in TCRF.
When TCF overflows from H'FFFF to H'0000, OVFH is set to 1 in TCSRF. If OVIEH in
TCSRF and IENTFH in IENR2 are both 1, an interrupt request is sent to the CPU.
b. Operation in 8-bit timer mode
When CKSH2 is set to 1 in TCRF, TCF operates as two independent 8-bit timers, TCFH and
TCFL. The TCFH/TCFL input clock is selected by CKSH2 to CKSH0/CKSL2 to CKSL0 in
TCRF.
When the OCRFH/OCRFL and TCFH/TCFL values match, CMFH/CMFL is set to 1 in
TCSRF. If IENTFH/IENTFL in IENR2 is 1, an interrupt request is sent to the CPU, and at the
same time, TMOFH pin/TMOFL pin output is toggled. If CCLRH/CCLRL in TCSRF is 1,
TCFH/TCFL is cleared. TMOFH pin/TMOFL pin output can also be set by TOLH/TOLL in
TCRF.
When TCFH/TCFL overflows from H'FF to H'00, OVFH/OVFL is set to 1 in TCSRF. If
OVIEH/OVIEL in TCSRF and IENTFH/IENTFL in IENR2 are both 1, an interrupt request is
sent to the CPU.
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