XC908AS60ACFU Motorola Semiconductor Products, XC908AS60ACFU Datasheet - Page 450

• Manufacturer Part Number: XC908AS60ACFU
• Description: MC68HC908AZ60A, MC68HC908AS60A Hcmos Microcontroller Unit Technical Data
• Manufacturer: Motorola Semiconductor Products

Timer Interface Module A (TIMA)
25.4.4.1 Unbuffered PWM Signal Generation
Technical Data
450
The value in the TIMA 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 TIMA counter modulo registers produces a PWM
period of 256 times the internal bus clock period if the prescaler select
value is $000 (see
The value in the TIMA channel registers determines the pulse width of
the PWM output. The pulse width of an 8-bit PWM signal is variable in
256 increments. Writing $0080 (128) to the TIMA channel registers
produces a duty cycle of 128/256 or 50%.
Any output compare channel can generate unbuffered PWM pulses as
described in
are unbuffered because changing the pulse width requires writing the
new pulse width value over the value currently in the TIMA channel
registers.
An unsynchronized write to the TIMA channel registers to change a
pulse width value could cause incorrect operation for up to two PWM
periods. For example, writing a new value before the counter reaches
the old value but after the counter reaches the new value prevents any
compare during that PWM period. Also, using a TIMA overflow interrupt
routine to write a new, smaller pulse width value may cause the compare
PTEx/TCHx
OVERFLOW
Timer Interface Module A (TIMA)
Pulse Width Modulation (PWM)
Figure 25-3. PWM Period and Pulse Width
PULSE
WIDTH
TIMA Status and Control Register
PERIOD
COMPARE
OUTPUT
OVERFLOW
COMPARE
OUTPUT
MC68HC908AZ60A — Rev 2.0
on page 449. The pulses
OVERFLOW
on page 457).
MOTOROLA
COMPARE
OUTPUT