
Timer Interface Module (TIM1)
Data Sheet
MC68HC908GR60A MC68HC908GR48A MC68HC908GR32A
260
Timer Interface Module (TIM1)
MOTOROLA
17.3.4.2 Buffered PWM Signal Generation
Channels 0 and 1 can be linked to form a buffered PWM channel whose output
appears on the T1CH0 pin. The TIM1 channel registers of the linked pair
alternately control the pulse width of the output.
Setting the MS0B bit in TIM1 channel 0 status and control register (T1SC0) links
channel 0 and channel 1. The TIM1 channel 0 registers initially control the pulse
width on the T1CH0 pin. Writing to the TIM1 channel 1 registers enables the TIM1
channel 1 registers to synchronously control the pulse width at the beginning of the
next PWM period. At each subsequent overflow, the TIM1 channel registers
(0 or 1) that control the pulse width are the ones written to last. T1SC0 controls and
monitors the buffered PWM function, and TIM1 channel 1 status and control
register (T1SC1) is unused. While the MS0B bit is set, the channel 1 pin, T1CH1,
is available as a general-purpose I/O pin.
NOTE:
In buffered PWM signal generation, do not write new pulse width 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 PWM signals.
17.3.4.3 PWM Initialization
To ensure correct operation when generating unbuffered or buffered PWM signals,
use the following initialization procedure:
1.
In the TIM1 status and control register (T1SC):
a.
Stop the TIM1 counter by setting the TIM1 stop bit, TSTOP.
b.
Reset the TIM1 counter and prescaler by setting the TIM1 reset bit,
TRST.
2.
In the TIM1 counter modulo registers (T1MODH:T1MODL), write the value
for the required PWM period.
3.
In the TIM1 channel x registers (T1CHxH:T1CHxL), write the value for the
required pulse width.
4.
In TIM1 channel x status and control register (T1SCx):
a.
Write 0:1 (for unbuffered output compare or PWM signals) or 1:0 (for
buffered output compare or PWM signals) to the mode select bits,
b.
Write 1 to the toggle-on-overflow bit, TOVx.
c.
Write 1:0 (polarity 1 — to clear output on compare) or 1:1 (polarity 0 —
to set output on compare) to the edge/level select bits, ELSxB:ELSxA.
The output action on compare must force the output to the complement
NOTE:
In PWM signal generation, do not program the PWM channel to toggle on output
compare. Toggling on output compare prevents reliable 0% duty cycle generation
and removes the ability of the channel to self-correct in the event of software error