Timer Interface B (TIMB)
Functional Description
MC68HC908MR16/MC68HC908MR32 — Rev. 4.0 Advance Information
MOTOROLA Timer Interface B (TIMB) 231
Use this method 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 compa re
interrupt routine. The output compare interrupt occurs at the end
of the current output compare pulse. The interrupt routi ne has until
the end of the counter overflow period to write the new value.
When changing to a larger output compa re value, e nable cha nnel
x TIMB overflow interrupts and write the new value in the TIMB
overflow interrupt routine. The TIMB 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.
12.4.3.2 Buffered Output Compare
Channels 0 and 1 can be linked to form a buffered output compare
channel whose output appears on the PTE1/TCH0B pin. The TIMB
channel registers of the linked pair alternately control the output.
Setting the MS0B bit in TIMB channel 0 status and control register
(TBSC0) links channel 0 and channel 1. The output com pare value in the
TIMB channel 0 registers initially controls the output on the
PTE1/TCH0B pin. Writing to the TIMB channel 1 registers enables the
TIMB channel 1 registers to synchronously control the output after the
TIMB overflows. At each subsequent overflow, the TIMB channel
registers (0 or 1) that control the output are the o nes written to last. TSC0
controls and monitors the buffered output compare function, and TIMB
channel 1 status and control register (TBSC1) is unused. While the
MS0B bit is set, the channel 1 pin, PTE2/TCH1 B, is available as a
general-purpose I/O pin.
NOTE: In buffered output compare operation, do not write new output comp are
values to the currently active channel registers. Writing to the active
channel registers is the same as generating unbuffered output
compares.