参数资料
型号: MC68HC05V7CB
厂商: FREESCALE SEMICONDUCTOR INC
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 2.1 MHz, MICROCONTROLLER, PDIP56
封装: SDIP-56
文件页数: 164/170页
文件大小: 980K
代理商: MC68HC05V7CB
SECTION 13: PULSE WIDTH MODULATOR
MOTOROLA
Page 79
MC68HC05V7 Specification Rev. 1.0
SECTION 13
PULSE WIDTH MODULATOR
The pulse width modulator (PWM) system has one 6-bit channel (PWMA). Preceding the
6-bit (
÷64) PWM are two programmable prescalers.The PWM frequency is selected by
choosing the desired divide option from the programmable prescalers. Note that the PWM
clock input is fosc, which is twice the bus frequency. The PWM frequency will be fosc/
(PSA+PSB+64) where PSA and PSB are the values selected by the A and B prescaler and
64 comes from the 6-bit modulus counter. See Table 13-1 for precise values. E is the
internal bus frequency fixed to half of the external oscillator frequency.
Figure 13-1:
PWM Block Diagram
13.1
FUNCTIONAL DESCRIPTION
The PWM is capable of generating signals from 0% to 100% duty cycle. A $00 in the PWM
Data Register yields an “low” output (0%), but a $3F yields a duty of 63/64. To achieve the
100% duty (“high” output), the polarity control bit is set to zero while the data register has
$00 in it.
When not in use, the PWM system can be shut off to save power by clearing the clock rate
select bits PSA0 and PSA1 in PWMCR.
Writes to the PWM data register are buffered and can therefore be performed at any time
without affecting the output signal. When the PWM subsystem is enabled, a write to the
PWM Control Register will become effective immediately.
6-BIT COUNTER
(
÷64)
PWM DATA
REGISTER
MODULUS &
COMPARATOR
PWM
PIN LOGIC
PWMA
÷1, ÷8, ÷16
fosc
PSA0
PSA1
PWM CONTROL REGISTER and BUFFER
HC05
DATA
BUS
POL
PWM DATA
BUFFER
SCLK
÷1-16
PSB2
PSB3
PSB0
PSB1
RCLK
Integer divide
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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