Difference between revisions of "PIC16F684"

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==Configuring I/O==
==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.
<pre>
<pre>
INIT_IO
INIT_IO
BCF STATUS,RP0 ;Bank 0
BANK0
CLRF PORTA ;Init PORTA - initially set to LOW
CLRF PORTA ;Init PORTA - initially set to LOW
MOVLW B'000101' ;Set RA<0> as input
MOVLW B'000101' ;Set RA<0> as input
MOVWF TRISA ; and set RA<5:1>
MOVWF TRISA ; and set RA<5:1>
; as outputs
; as outputs

BANK1
BSF STATUS,RP0 ;Bank 1
CLRF PORTC ;Init PORTC - initially set to LOW
CLRF PORTC ;Init PORTC - initially set to LOW
MOVLW B'000000' ;Set RC<5:0> as outputs
MOVLW B'000000' ;Set RC<5:0> as outputs
Line 48: Line 50:
MOVLW B'000001'
MOVLW B'000001'
MOVWF ANSEL ;Set AN<0> (RA<0>) to Analog input
MOVWF ANSEL ;Set AN<0> (RA<0>) to Analog input
; RA<5:1> remain digital I/O
; 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
RETURN
</pre>

''Notice that the two following bits of code are equivalent:''

<pre>
CLRF PORTA
</pre>
''and''
<pre>
MOVLW B'000000'
MOVWF PORTA
</pre>
</pre>


==Setting Up for PWM Output==
==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:
<pre>
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
</pre>

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:

<pre>
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
</pre>

Latest revision as of 18:25, 11 July 2006

Overview

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

IMPORTANT: See PIC16F684 Registers for detailed information on registers.

Pinout

Pic16f684 pinout.png
Description of Pinout Labels
Label Description
+ 5 V
Ground
External Voltage Reference
PORTA/PORTC Programmable I/O
A/D Channel
External Interrupt Input
PWM Output

Initialization

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