MC68HC08AZ32A Datasheet, PDF (241/312 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Functional Description
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.
17.3.3.2 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.
Channels 2 and 3 can be linked to form a buffered output compare channel whose output appears on the
PTF0/TACH2 pin. The TIMA channel registers of the linked pair alternately control the output.
Setting the MS2B bit in TIMA channel 2 status and control register (TASC2) links channel 2 and
channel 3. The output compare value in the TIMA channel 2 registers initially controls the output on the
PTF0/TACH2 pin. Writing to the TIMA channel 3 registers enables the TIMA channel 3 registers to
synchronously control the output after the TIMA overflows. At each subsequent overflow, the TIMA
channel registers (2 or 3) that control the output are the ones written to last. TASC2 controls and monitors
the buffered output compare function, and TIMA channel 3 status and control register (TASC3) is unused.
While the MS2B bit is set, the channel 3 pin, PTF1/TACH3, is available as a general-purpose I/O pin.
Channels 4 and 5 can be linked to form a buffered output compare channel whose output appears on the
PTF2 pin. The TIMA channel registers of the linked pair alternately control the output.
Setting the MS4B bit in TIMA channel 4 status and control register (TASC4) links channel 4 and
channel 5. The output compare value in the TIMA channel 4 registers initially controls the output on the
PTF2 pin. Writing to the TIMA channel 5 registers enables the TIMA channel 5 registers to synchronously
control the output after the TIMA overflows. At each subsequent overflow, the TIMA channel registers (4
or 5) that control the output are the ones written to last. TASC4 controls and monitors the buffered output
compare function and TIMA channel 5 status and control register (TASC5) is unused. While the MS4B bit
is set, the channel 5 pin, PTF3, is available as a general-purpose I/O pin.
NOTE
In buffered output compare operation, do not write new output compare
values to the currently active channel registers. User software should track
the currently active channel to prevent writing a new value to the active
channel. Writing to the active channel registers is the same as generating
unbuffered output compares.
MC68HC08AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
241