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Chapter 7 16-bit Timer
VII - 30
16-bit High Precision PWM Output
(5) Select fosc as clock source by the TM7CK1-0
flag of the TM7MD1 register. Also, select 1/2
dividing as count clock source by the TM7PS1-
0 flag.
(6) Set the PWM output cycle to the timer 7 preset
register 1 (TM7PR1). To be 400 Hz by divided
10 MHz, set as follows :
25000 - 1 = 24999 (x'61a7')
At that time, the same value is loaded to the
timer 7 compare register 1 (TM7OC1), and the
timer 7 binary counter (TM7BC) is initialized to
x'0000'.
(7) Set the "H" period of the PWM output to the
timer 7 preset register 2 (TM7PR2). To be a
1/4 duty of 25000 dividing, set as follows ;
25000 / 4 = 6250 (x'186a')
At that time, the same value is loaded to the
timer 7 compare register 2 (TM7OC2).
(8) Set the TM7EN flag of the TM7MD1 register to
"1" to start timer 7.
Setup Procedure
(5) Select the count clock source.
TM7MD1 (x'3F78')
bp1-0 : TM7CK1-0 = 00
bp3-2 : TM7PS1-0 = 01
(6) Set the PWM output cycle.
TM7PR1 (x'3F75',x'3F74') = x'61a7'
(7) Set the "H" period of the PWM
output.
TM7PR2 (x'3F7D',x'3F7C')=x'186a'
(8) Start the timer operation.
TM7MD1 (x'3F78')
bp4 : TM7EN = 1
Description
TM7BC counts up from x'0000'. The PWM source waveform outputs "H" until TM7BC matches the
set value of the TM7OC2 register. Once they matches, it outputs "L". After that, TM7BC continues to
count up, once TM7BC matches the TM7OC1 register to be cleared, the PWM source waveform
outputs "H" again and TM7BC counts up from x'0000' again. TM7IO pin outputs one count clock
delay of the PWM source waveform.
In the initial state of the PWM output, it is changed from "L" output to "H" output as the PWM
output is selected by the TM7PWM flag of the TM7MD register.
Set as the set value of TM7OC2 ≤ the set value of TM7OC1. If it is set as the set value of
TM7OC2 > the set value of TM7OC1, the PWM output is a "H" fixed output.
Write to preset register should be done while timer is stopped or within timer interrupt pro-
cessing.
And use MOVW instruction for write to preset register.