Datasheet
I/O Registers
MC68HC908GR16A Data Sheet, Rev. 1.0
Freescale Semiconductor 229
NOTE
Before enabling a TIM channel register for input capture operation, make
sure that the PTD/TCHx 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 output when the TIM counter overflows. When channel x is an input capture channel, TOVx has no
effect. Reset clears the TOVx bit.
1 = Channel x pin toggles on TIM counter overflow.
0 = Channel x pin does not toggle on TIM counter overflow.
NOTE
When TOVx is set, a TIM 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 bit is at 1, setting the CHxMAX bit forces the duty cycle of buffered and unbuffered
PWM signals to 100%. As Figure 18-12 shows, the CHxMAX bit takes effect in the cycle after it is set
or cleared. The output stays at the 100% duty cycle level until the cycle after CHxMAX is cleared.
NOTE
The 100% PWM duty cycle is defined as a continuous high level if the PWM
polarity is 1 and a continuous low level if the PWM polarity is 0. Conversely,
a 0% PWM duty cycle is defined as a continuous low level if the PWM
polarity is 1 and a continuous high level if the PWM polarity is 0.
Figure 18-12. CHxMAX Latency
Table 18-3. Mode, Edge, and Level Selection
MSxB MSxA ELSxB ELSxA Mode Configuration
X0 0 0
Output preset
Pin under port control; initial output level high
X 1 0 0 Pin under port control; initial output level low
00 0 1
Input capture
Capture on rising edge only
0 0 1 0 Capture on falling edge only
0 0 1 1 Capture on rising or falling edge
01 0 0
Output compare
or PWM
Software compare only
0 1 0 1 Toggle output on compare
0 1 1 0 Clear output on compare
0 1 1 1 Set output on compare
1X 0 1
Buffered output
compare or
buffered PWM
Toggle output on compare
1 X 1 0 Clear output on compare
1 X 1 1 Set output on compare
OUTPUT
OVERFLOW
TCHx
PERIOD
CHxMAX
OVERFLOW OVERFLOW OVERFLOW OVERFLOW
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE