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Application Note
AN_289 FT51A Programming Guide
Version 1.0
Document Reference No.: FT_000962 Clearance No.: FTDI# 483
107
Copyright © 2015 Future Technology Devices International Limited
0x92
PWM comparator MSB register 6
0x93
PWM comparator LSB register 7
0x94
PWM comparator MSB register 7
0x95
PWM out toggle enable register 0
0x96
PWM out toggle enable register 1
0x97
PWM out toggle enable register 2
0x98
PWM out toggle enable register 3
0x99
PWM out toggle enable register 4
0x9A
PWM out toggle enable register 5
0x9B
PWM out toggle enable register 6
0x9C
PWM out toggle enable register 7
0x9D
PWM out clear enable register
0x9E
PWM control block register
0x9F
PWM initialization register
Table 2.135 PWM Register Addresses
Pulse Width Modulation (PWM) is the simplest form of duty cycle control. Consider the simple
square wave in the figure below.
Figure 2.7 Square wave with 50 % duty cycle
In this example, the width of the high pulse is equal to the width of the low pulse. This waveform
has a 50 % duty cycle. If the amplitude of this square wave is 5V, the RMS voltage can be
calculated as:
VRMS = VPEAK * SQRT (Duty Cycle)
VRMS = 5V * SQRT (.50)
VRMS = 3.54V
If the duty cycle is reduced, then the RMS voltage reduces. This is illustrated in the following
example which shows a waveform with a 20% duty cycle: