Operation Of Pwm Timer Function - Fujitsu Semiconductor Controller MB89950/950A Hardware Manual

CHAPTER 7 8-BIT PWM TIMER
7.6

Operation of PWM Timer Function

This section describes the operation of the PWM timer function of the 8-bit PWM timer.
I Operation of PWM timer function
Figure 7.6-1 "PWM timer function settings" shows the settings required to operate as the PWM timer
function.
CNTR
COMR
On activation, the counter starts to count up from "00
PWM pin (PWM) outputs (PWM waveform) an "H" level until the counter value matches the value set in
the COMR register. From the match until the counter value overflows (FF
an "L" level.
Figure 7.6-2 "Example of PWM waveform output (PWM pin)" shows the PWM waveforms output from
the PWM pin.
For COMR register value of "00
Counter value 00
PWM waveform
For COMR register value of "80
Counter value
PWM waveform
For COMR register value of "FF
Counter value
PWM waveform
Note:
Do not change the count clock cycle (CNTR: P1, P0) during operation of the PWM timer function
(CNTR: TPE = "1").
Reference:
When the PWM timer function is selected, the PWM pin maintains its existing level when the counter is
stopped (CNTR: TPE = "0").
134
Figure 7.6-1 PWM timer function settings
Bit 7 Bit 6 Bit 5
P/TX — P1
1
Sets "H" width of pulse (compare value).
Figure 7.6-2 Example of PWM waveform output (PWM pin)
" (duty ratio = 0%)
H
H
H
L
" (duty ratio = 50%)
H
00
H
H
L
" (duty ratio = 99.6%)
H
00
H
H
L
One count clock cycle width
Bit 4 Bit 3 Bit 2 Bit 1
P0 TPE TIR OE
1 X 1
" on the rising edge of the selected count clock. The
H
FF 00
H H
80 FF 00
H H
H
FF 00
H H
Bit 0
TIE
: Used bit
X
: Unused bit
X
1 : Set "1".
--> 00 ), the PWM pin outputs
H H