MC68HC908RK2 Datasheet, PDF (201/232 Pages) Motorola, Inc – Microcontroller Unit

Timer Interface Module (TIM)
Functional Description
15.5.5 Buffered Output Compare
Channels 0 and 1 can be linked to form a buffered output compare
channel whose output appears on the PTB2/TCH0 pin. The TIM channel
registers of the linked pair alternately control the output.
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 ones 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.
15.5.6 Pulse-Width Modulation (PWM)
By using the toggle-on-overflow feature with an output compare channel,
the TIM can generate a pulse-width modulation (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 15-3 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 if the state of the PWM
pulse is logic 0.
MC68HC908RK2 — Rev. 4.0
MOTOROLA
Timer Interface Module (TIM)
Advance Information
201