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Timer Interface (TIMA-6)
General Release Specification
MC68HC908AT32
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Rev. 2.0
460
Timer Interface (TIMA-6)
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MOTOROLA
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/TACH4 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
(TSC4) links channel 4 and channel 5. The output compare value in the
TIMA channel 4 registers initially controls the output on the
PTF2/TACH4 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/TACH5, 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. Writing to the active
channel registers is the same as generating unbuffered output
compares.
25.4.4 Pulse Width Modulation (PWM)
By using the toggle-on-overflow feature with an output compare
channel, the TIMA can generate a PWM signal. The value in the TIMA
counter modulo registers determines the period of the PWM signal. The
channel pin toggles when the counter reaches the value in the TIMA
counter modulo registers. The time between overflows is the period of
the PWM signal.
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