參數(shù)資料
型號: MC68HC05BS8FB
廠商: MOTOROLA INC
元件分類: 微控制器/微處理器
英文描述: 8-BIT, MROM, 2.2 MHz, MICROCONTROLLER, PQFP44
封裝: QFP-44
文件頁數(shù): 82/128頁
文件大?。?/td> 752K
代理商: MC68HC05BS8FB
MC68HC05BS8
MOTOROLA
7-1
PULSE WIDTH MODULATION
7
PULSE WIDTH MODULATION
The MC68HC05BS8 has two independent PWMs; one general purpose (GPWM) and one raster
positioning (RSPWM). They are controlled by the PWM registers located at $0010 and $0011.
7.1
General Purpose Pulse Width Modulator
The GPWM consists of a comparator and a 6-bit free-running counter driven by the internal bus
clock. The counter runs from $00 to $3E and rolls over back to $00. Whenever the GPWM value
in the GPWM register is greater than the running counter, the output of the GPWM pin will be
“high” (See Figure 7-1).
To reduce the occurrence of fast logic switching edges on the PCB, the GPWM output is
connected to the output pin via an on chip resistor of nominal value of 5K
. In this way, for use
with DC controls the RC lter capacitor is connected externally directly to the output. A further
advantage is that the PWM logic signal has only to overcome modest on-chip capacitances and
thus supply current spikes are signicantly reduced.
The GPWM output can be congured as an open drain output by setting ODE bit in the GPWM
register. It should be noted that the diode associated with the P-channel device is still connected
to the output pin and therefore the normal voltage limitations apply, i.e. up to VDD. Figure 7-2
shows a schematic of the GPWM output.
Figure 7-1 GPWM Timing Example
8
s
23.5
s
31.5
s
Frame rate=32KHz
GPWM
GPWM data = 16 = 01000
Internal clock = 2MHz
TPG
55
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