参数资料
型号: M38514E6-XXXFP
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 4 MHz, MICROCONTROLLER, PDSO42
封装: 0.450 INCH, 0.80 MM PITCH, PLASTIC, SSOP-42
文件页数: 37/93页
文件大小: 1137K
代理商: M38514E6-XXXFP
Rev.1.01
Oct 15, 2003
page 40 of 89
3851 Group (Built-in 24 KB or more ROM)
PULSE WIDTH MODULATION (PWM)
The 3851 group (built-in 24 KB or more ROM) has a PWM func-
tion with an 8-bit resolution, based on a signal that is the clock
input XIN or that clock input divided by 2.
Data Setting
The PWM output pin also functions as port P44. Set the PWM
period by the PWM prescaler, and set the “H” term of output pulse
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 X (n+1) / f(XIN)
= 31.875 X (n+1)
s
(when f(XIN) = 8 MHz,count source selection bit = “0”)
Output pulse “H” term = PWM period X m / 255
= 0.125 X (n+1) X m
s
(when f(XIN) = 8 MHz,count source selection bit = “0”)
Fig. 40 Timing of PWM period
Fig. 41 Block diagram of PWM function
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.
31.875 m (n+1)
255
s
T = [31.875 (n+1)]
s
PWM output
m: Contents of PWM register
n : Contents of PWM prescaler
T : PWM period (when f(XIN) = 8 MHz, count
source selection bit = “0”)
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
XIN
Port P44 latch
PWM enable bit
Port P44
PWM prescaler
(XCIN at low-speed mode)
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