
Timer Interface Module (TIM)
Functional Description
MC68HC(9)08XK48 — Rev. 4.0
Advance Information
MOTOROLA
Timer Interface Module (TIM)
253
compare value may cause the compare to be missed. The timer may
pass the new value before it is written.
Use these methods to synchronize unbuffered changes in the output
compare value on channel x:
When changing to a smaller value, enable channel x output
compare interrupts and write the new value in the output compare
interrupt routine. The output compare interrupt occurs at the end
of the current output compare pulse. The interrupt routine has until
the end of the counter overflow period to write the new value.
When changing to a larger output compare value, enable channel
x timer overflow interrupts and write the new value in the timer
overflow interrupt routine. The timer overflow interrupt occurs at
the end of the current counter overflow period. Writing a larger
value in an output compare interrupt routine (at the end of the
current pulse) could cause two output compares to occur in the
same counter overflow period.
16.4.3.2 Buffered Output Compare
Channels 0 and 1 can be linked to form a buffered output compare
channel whose output appears on the PTE4/TCH0 pin. The timer
channel registers of the linked pair alternately control the output.
Setting the MS0B bit in timer channel 0 status and control register
(TSC0) links channel 0 and channel 1. The output compare value in the
timer channel 0 registers initially controls the output on the PTE4/TCH0
pin. Writing to the timer channel 1 registers enables the timer channel 1
registers to synchronously control the output after the timer overflows. At
each subsequent overflow, the timer channel registers (0 or 1) that
control the output are the ones written to last. TSC0 controls and
monitors the buffered output compare function, and timer channel 1
status and control register (TSC1) is unused. While the MS0B bit is set,
the channel 1 pin, PTE5/TCH1, is available as a general-purpose I/O
pin.