MSE908JB8 FREESCALE [Freescale Semiconductor, Inc], MSE908JB8 Datasheet - Page 3

• Manufacturer Part Number: MSE908JB8
• Description: Mask Set Errata
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

Glitch on Timer Buffered PWM Output
In timer buffered PWM operation, when a timer overflow (TOF) event or an output compare (OC) event
coincides with a write to either pair of the timer channel registers (TCHxH/L), the duty cycle at the PWM
output glitches to 0% or 100% momentarily, then returns to proper operation.
To avoid the glitches when changing the PWM duty cycle, do not write to either pair of the timer channel
registers at the TOF or OC.
For example, in the TOF interrupt service routine: If the OC occurs near the last TOF, write to the timer
channel registers after the OC; if the OC occurs near the next TOF, write to the timer channel registers
before the OC. A write to the channel register high byte (TCHxH) should immediately followed by a write
to the low byte (TCHxL) to avoid TOF or OC occurring between the writes. Instruction cycle times must
be included when making timing calculations.
The figure below shows a typical timer buffered PWM output waveform, indicating the TOF and OC
events.
Freescale Semiconductor
10 Ω
V
V
DD
DD
Mask Set Errata for 908JB8, Mask 3K45H
0.1 µF
10 µF
+
V
MCU
SS
0.1 µF
4.7 µF
+
V
REG
SE30-PWM
3