MC68HC908KX8 Datasheet, PDF (229/310 Pages) Motorola, Inc – Microcontrollers

Timer Interface Module (TIM)
Functional Description
Setting the MS0B bit in TIM channel 0 status and control register (TSC0)
links channel 0 and channel 1. The output compare value in the TIM
channel 0 registers initially controls the output on the TCH0 pin. Writing
to the TIM channel 1 registers enables the TIM channel 1 registers to
synchronously control the output after the TIM overflows. At each
subsequent overflow, the TIM channel registers (0 or 1) that control the
output are the 1s written to last. TSC0 controls and monitors the buffered
output compare function, and TIM channel 1 status and control register
(TSC1) is unused. While the MS0B bit is set, the channel 1 pin, TCH1,
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.
16.4.6 Pulse-Width Modulation (PWM)
By using the toggle-on-overflow feature with an output compare channel,
the TIM can generate a PWM signal. The value in the TIM counter
modulo registers determines the period of the PWM signal. The channel
pin toggles when the counter reaches the value in the TIM counter
modulo registers. The time between overflows is the period of the PWM
signal.
As Figure 16-3 shows, the output compare value in the TIM channel
registers determines the pulse width of the PWM signal. The time
between overflow and output compare is the pulse width. Program the
TIM to clear the channel pin on output compare if the state of the PWM
pulse is logic 1. Program the TIM to set the pin on overflow if the state of
the PWM pulse is logic 0.
The value in the TIM counter modulo registers and the selected
prescaler output determines the frequency of the PWM output. The
frequency of an 8-bit PWM signal is variable in 256 increments. Writing
$00FF (255) to the TIM counter modulo registers produces a PWM
period of 256 times the internal bus clock period if the prescaler select
value is $000. See 16.8.1 TIM Status and Control Register.
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 — Rev. 1.0
MOTOROLA
Timer Interface Module (TIM)
Technical Data
229