PIC16F684

Overview

For a complete list of features, see this printout from the datasheet.

IMPORTANT: See PIC16F684 Registers for detailed information on registers.

Pinout

Description of Pinout Labels

Label	Description
$V_{DD}\,$	+ 5 V
$V_{SS}\,$	Ground
$V_{REF}\,$	External Voltage Reference
$RA\#/RC\#\,$	PORTA/PORTC Programmable I/O
$AN\#\,$	A/D Channel
$INT\,$	External Interrupt Input
$P1A/B/C/D\,$	PWM Output

Configuring I/O

This section shows two sections of code that are used for setting up the I/O of the PIC. The INIT_IO function sets up the ports by setting their default value and their direction. The second function, INIT_ADC sets up the A/D converter.

INIT_IO	
	BCF 		STATUS,RP0 		;Bank 0
	CLRF 		PORTA 			;Init PORTA - initially set to LOW
	MOVLW 	B'000101'			;Set RA<0> as input
	MOVWF 		TRISA 			;	and set RA<5:1>
						;	as outputs

	BSF 		STATUS,RP0 		;Bank 1
	CLRF 		PORTC 			;Init PORTC - initially set to LOW
	MOVLW 	B'000000'			;Set RC<5:0> as outputs
	MOVWF 		TRISC

	CLRF		ANSEL			;Set all pins initially to digital I/O
	MOVLW	B'000001'
	MOVWF		ANSEL			;Set AN<0> (RA<0>) to Analog input
						;	RA<5:1> remain digital I/O
	RETURN

INIT_ADC
	BCF 		STATUS,RP0 		;Bank 0
        MOVLW   B'00000001'			; Set output to left justified
	MOVWF   	ADCON0			; Select AN<0> (RA<0>) as input
						; Internal Vref
						; Start ADC ON

	BSF 		STATUS,RP0 		;Bank 1
	CLRF		ADCON1
        MOVLW   B'00100000' 		        ;Set Clock TAD to 1.6us (Fosc/32)
        MOVWF   	ADCON1

	RETURN

Notice that the two following bits of code are equivalent:

        CLRF            PORTA

and

	MOVLW 	B'000000'
	MOVWF 		PORTA

Setting Up for PWM Output

Using the built-in PWM functionality is very useful, but it a little tricky to setup and use. First, you need to initialize the PWM by setting the mode, initial duty cycle, and frequency:

INIT_PWM
	BCF 		STATUS,RP0 		;Bank 0
	MOVLW	B'10001100'			;Half-Bridge Output, Dual-Mode PWM
	MOVWF		CCP1CON
	MOVLW	B'00000100'			;Timer2 enabled with prescale 1
	MOVWF		T2CON
	MOVLW	B'01111111'			;50% duty cycle
	MOVWF		CCPR1L	

	BSF 		STATUS,RP0 		;Bank 1
	MOVLW	0xFF
	MOVWF		PR2			;Set frequency to 19.53 kHz

	RETURN

Next is setting the desired duty cycle. A 0% duty cycle will correspond to 5v on P1A and 0v on P1B. A 100% duty cycle will correspond to the opposite, 0v on P1A and 5v on P1B. The duty cycle is a 10-bit number that spans two registers, CCPR1L<7:0> and CCP1CON<5:4>. To set a 100% duty cycle, you will need code like this:

UPDATE_PWM
	BCF 		STATUS,RP0 		;Bank 0
	MOVLW	B'11111111'			; Set 8 MSbs to the CCPR1L register
	MOVWF	        CCPR1L
	BSF		CCP1CON,5		; set 2 LSbs to 1
	BSF		CCP1CON,4