SYNPWM datasheet(25/57 Pages) FEELING

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FM8P73B

Web site: http://www.feeling-tech.com.tw

Rev1.0 Nov 20, 2013

P.25/FM8P73B

FEELING

TECHNOLOGY

2.4

Pulse Width Modulation (PWM)

FM8P73B provides one PWM output shared with TMR1/2, TMR1 becomes the period of PWM1 and TMR2 will be

the duty of PWM1.

If the system frequency is 4MHz, the range of PWM period could be from 0.5us to 8,192ms.

2.4.1

Normal PWM mode

In this mode, it is a general purpose PWM mode. Please refer to the sample program and timing diagram below.

Note : When PWM duty or period needed to be changed, the auto-load control bit of the timer (TxLOAD) must be

cleared before new data writes to latch register. If this bit still set, the data written to latch register would

be load into counter register immediately and cause PWM output anomaly.

Example 2.2: PWM1 Setting (Normal mode)

Address

Code

#include

<8P73B.ASH>

…

//Set PWM1 Period

MOVIA

0x61

n+1

MOVAR

T1CON

;Set source: 4MHz IRC (250nS) Prescaler 1:2

n+2

MOVIA

0x80

n+3

MOVAR

PWM1CON

;Set PWM interrupt rate 1:1, output on IOA0

n+4

MOVIA

0x0F

n+5

MOVAR

T1LA

;Set period (0x0F down count to 0x00)

;Period time = 250ns x 16 x 2 = 8uS

//Set PWM1 Duty

n+6

MOVIA

0x61

n+7

MOVAR

T2CON

;Set source 4MHz IRC (250nS) Prescaler 1:2

n+8

MOVIA

0x07

n+9

MOVAR

T2LA

;Set Duty (0x07 down count to 0x00)

;Duty time = 250ns x 8 x2 = 4uS

n+10

BSR

T1CON,T1EN_B

;Start PWM1

n+11

MOVIA

0x81

n+12

MOVAR

INTEN

;Enable global & PWM1 interrupt

n+13

CLRR

INTFLAG

;Clear interrupt flag

Note: The PWM duty (Timer2) must be smaller than PWM period (Timer1).

Figure 2.5: Normal PWM Output Waveform

TMR2 counter:

PWM1P Output:

PWM Duty

PWM P eriod

TMR1 counter:

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