MC908MR32CFUE Datasheet, PDF (224/282 Pages) Freescale Semiconductor, Inc – Microcontrollers

Timer Interface A (TIMA)
4. In TIMA channel x status and control register (TSCx):
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, MSxB–MSxA. (See Table 16-2.)
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 of the pulse width level. (See Table 16-2.)
NOTE
In PWM signal generation, do not program the PWM channel to toggle on
output compare. Toggling on output compare prevents reliable 0 percent
duty cycle generation and removes the ability of the channel to self-correct
in the event of software error or noise. Toggling on output compare can also
cause incorrect PWM signal generation when changing the PWM pulse
width to a new, much larger value.
5. In the TIMA status control register (TASC), clear the TIMA stop bit, TSTOP.
Setting MS0B links channels 0 and 1 and configures them for buffered PWM operation. The TIMA
channel 0 registers (TACH0H–TACH0L) initially control the buffered PWM output. TIMA status control
register 0 (TASC0) controls and monitors the PWM signal from the linked channels. MS0B takes priority
over MS0A.
Setting MS2B links channels 2 and 3 and configures them for buffered PWM operation. The TIMA
channel 2 registers (TACH2H–TACH2L) initially control the buffered PWM output. TIMA status control
register 2 (TASC2) controls and monitors the PWM signal from the linked channels. MS2B takes priority
over MS2A.
Clearing the toggle-on-overflow bit, TOVx, inhibits output toggles on TIMA overflows. Subsequent output
compares try to force the output to a state it is already in and have no effect. The result is a 0 percent duty
cycle output.
Setting the channel x maximum duty cycle bit (CHxMAX) and setting the TOVx bit generates a 100
percent duty cycle output. (See 16.7.4 TIMA Channel Status and Control Registers.)
16.4 Interrupts
These TIMA sources can generate interrupt requests:
• TIMA overflow flag (TOF) — The timer overflow flag (TOF) bit is set when the TIMA counter
reaches the modulo value programmed in the TIMA counter modulo registers. The TIMA overflow
interrupt enable bit, TOIE, enables TIMA overflow interrupt requests. TOF and TOIE are in the
TIMA status and control registers.
• TIMA channel flags (CH3F–CH0F) — The CHxF bit is set when an input capture or output compare
occurs on channel x. Channel x TIMA CPU interrupt requests are controlled by the channel x
interrupt enable bit, CHxIE.
16.5 Wait Mode
The WAIT instruction puts the MCU in low power-consumption standby mode.
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
224
Freescale Semiconductor