MC68HC908QT2CDW Freescale Semiconductor, MC68HC908QT2CDW Datasheet - Page 125
Manufacturer Part Number
IC MCU 1.5K FLASH W/ADC 8-SOIC
Specifications of MC68HC908QT2CDW
LVD, POR, PWM
Number Of I /o
Program Memory Size
1.5KB (1.5K x 8)
Program Memory Type
128 x 8
Voltage - Supply (vcc/vdd)
2.7 V ~ 5.5 V
-40°C ~ 85°C
Package / Case
8-SOIC (5.3mm Width), 8-SOP, 8-SOEIAJ
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
22.214.171.124 PWM Initialization
To ensure correct operation when generating unbuffered or buffered PWM signals, use the following
1. In the TIM status and control register (TSC):
a. Stop the TIM counter by setting the TIM stop bit, TSTOP.
b. Reset the TIM counter and prescaler by setting the TIM reset bit, TRST.
2. In the TIM counter modulo registers (TMODH:TMODL), write the value for the required PWM
3. In the TIM channel x registers (TCHxH:TCHxL), write the value for the required pulse width.
4. In TIM 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
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
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 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 TIM status control register (TSC), clear the TIM stop bit, TSTOP.
Setting MS0B links channels 0 and 1 and configures them for buffered PWM operation. The TIM channel
0 registers (TCH0H:TCH0L) initially control the buffered PWM output. TIM status control register 0
(TSCR0) controls and monitors the PWM signal from the linked channels. MS0B takes priority over MS0A.
Clearing the toggle-on-overflow bit, TOVx, inhibits output toggles on TIM 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% duty cycle
Setting the channel x maximum duty cycle bit (CHxMAX) and setting the TOVx bit generates a 100% duty
cycle output. See
14.9.4 TIM Channel Status and Control
The following TIM sources can generate interrupt requests:
TIM overflow flag (TOF) — The TOF bit is set when the TIM counter reaches the modulo value
programmed in the TIM counter modulo registers. The TIM overflow interrupt enable bit, TOIE,
enables TIM overflow CPU interrupt requests. TOF and TOIE are in the TIM status and control
TIM channel flags (CH1F:CH0F) — The CHxF bit is set when an input capture or output compare
occurs on channel x. Channel x TIM CPU interrupt requests are controlled by the channel x
interrupt enable bit, CHxIE. Channel x TIM CPU interrupt requests are enabled when CHxIE =1.
CHxF and CHxIE are in the TIM channel x status and control register.
MC68HC908QY/QT Family Data Sheet, Rev. 6