
3802 GROUP USER’S MANUAL
1-28
HARDWARE
Data bus
Count source
selection bit
“0”
“1”
PWM
prescaler pre-latch
PWM
register pre-latch
PWM
prescaler latch
PWM
register latch
Transfer control circuit
PWM register
1/2
X
IN
Port P5
6
latch
PWM enable bit
Port P5
6
PWM prescaler
PULSE WIDTH MODULATION (PWM)
The 3802 group has a PWM function with an 8-bit resolution,
based on a signal that is the clock input X
IN
or that clock input di-
vided by 2.
Data Setting
The PWM output pin also functions as port P5
6
. Set the PWM pe-
riod by the PWM prescaler, and set the period during which the
output pulse is an “H” by the PWM register.
If the value in the PWM prescaler is n and the value in the PWM
register is m (where n = 0 to 255 and m = 0 to 255) :
PWM period = 255
(n+1)/f(X
IN
)
= 51
(n+1)
μ
s (when X
IN
= 5 MHz)
Output pulse “H” period = PWM period
m/255
= 0.2
(n+1)
m
μ
s
(when X
IN
= 5 MHz)
PWM Operation
When bit 0 (PWM enable bit) of the PWM control register is set to
“1”, operation starts by initializing the PWM output circuit, and
pulses are output starting at an “H”.
If the PWM register or PWM prescaler is updated during PWM
output, the pulses will change in the cycle after the one in which
the change was made.
Fig. 26 Timing of PWM cycle
Fig. 27 Block diagram of PWM function
51
m
(n+1)
255
μ
s
T = [51
(n+1)]
μ
s
PWM output
m: Contents of PWM register
n : Contents of PWM prescaler
T : PWM cycle (when X
IN
= 5
MHz)
FUNCTIONAL DESCRIPTION