Timer Interface A (TIMA)
I/O Registers
MC68HC908MR16/MC68HC908MR32 — Rev. 4.0 Advance Information
MOTOROLA Timer Interface A (TIMA) 221
NOTE: Before enabling a TIMA channel register for input capture operation,
make sure that the PTEx/TACHx pin is stable for at least two bus clocks.
TOVx — Toggle-On-Overflow Bit
When channel x is an output compare channel, this read/write bit
controls the behavior of the channel x outp ut wh en th e TIMA count er
overflows. When channel x is an input capture channel, TOVx has no
effect. Reset clears the TOVx bit.
1 = Channel x pin toggles on TIMA counter overflow.
0 = Channel x pin does not toggle on TIMA counter overflow.
NOTE: When TOVx is set, a TIMA counter overflow takes precedence over a
channel x output compare if both occur at the same time.
CHxMAX — Channel x Maximum Duty Cycle Bit
When the TOVx is at logic 1 and clear output on compare is selected,
setting the CHxMAX bit forces the duty cycle of buffered and
unbuffered PWM signals to 100 percent. As Figure 11-8 shows,
CHxMAX bit takes effect in the cycle after it is set or cleared. The
output stays at 100 percent duty cycle level until the cycle after
CHxMAX is cleared.
NOTE: The PWM 0 percent duty cycle is defined as output low all of the time.To
generate the 0 percent duty cycle select clear output on compare and
then clear the TOVx bit (CHxMAX = 0). The PWM 100 percent duty cycle
is defined as output high all of the time. To gen erate the 100 percent duty
cycle, use the CHxMAX bit in the TSCx register.
Figure 11-8. CHxMAX Latency
OUTPUT
OVERFLOW
PTEx/TCHx
PERIOD
CHxMAX
OVERFLOW OVERFLOW OVERFLOW OVERFLOW
COMPARE OUTPUT
COMPARE OUTPUT
COMPARE OUTPUT
COMPARE
TOVx