MC68HC08AZ32A Datasheet, PDF (388/456 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Timer Interface Module A (TIMA)
using a TIMA overflow interrupt routine to write a new, smaller output
compare value may cause the compare to be missed. The TIMA may
pass the new value before it is written.
Use the following 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 TIMA
overflow interrupts and write the new value in the TIMA overflow
interrupt routine. The TIMA 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.
22.4.3.2 Buffered Output Compare
Channels 0 and 1 can be linked to form a buffered output compare
channel whose output appears on the PTE2/TACH0 pin. The TIMA
channel registers of the linked pair alternately control the output.
Setting the MS0B bit in TIMA channel 0 status and control register
(TASC0) links channel 0 and channel 1. The output compare value in the
TIMA channel 0 registers initially controls the output on the
PTE2/TACH0 pin. Writing to the TIMA channel 1 registers enables the
TIMA channel 1 registers to synchronously control the output after the
TIMA overflows. At each subsequent overflow, the TIMA channel
registers (0 or 1) that control the output are the ones written to last.
TASC0 controls and monitors the buffered output compare function and
TIMA channel 1 status and control register (TASC1) is unused. While the
MS0B bit is set, the channel 1 pin, PTE3/TACH1, is available as a
general-purpose I/O pin.
Technical Data
388
MC68HC08AZ32A — Rev 1.0
Timer Interface Module A (TIMA)
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