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
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle V_{DD}\,}	+ 5 V
$V_{SS}\,$	Ground
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle V_{REF}\,}	External Voltage Reference
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle RA\#/RC\#\,}	PORTA/PORTC Programmable I/O
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle AN\#\,}	A/D Channel
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle INT\,}	External Interrupt Input
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 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