pickit2 help

jay543_uk · Jul 24, 2008

hi all, iv started using a pickit2 clone and its working fine but the only problem is that it is connected to portb rb4 and rb5 on my 16f876a but for me to test my circuit proply i need to use these pins for an output at the same time as testing with the pickit2, can any one advise me if i can do this.

thanks jason

Nigel Goodwin · Jul 24, 2008

Don't program in-circuit, take the chip out, program it, then put it back in the target board - this way you have no restrictions at all on your target board.

richard.c · Jul 24, 2008

Hi,

Your port usage seems wrong - the Pickit2 uses Rb6 and Rb7 for the clk and data signals - I assume it is these your really mean.

If you are wanting to In Ciruit program, with Rb6 and Rb7 connected to your circuit, then you must use a manual DP switch or some form of electronic switch to isolate your circuit and the Pickit from each other.
See Microchips Pickit2 user manual for clear details.

If you are wanting to use the Debugger function ,then no you cannot, as Mclr, Data and Clk must be dedicated to the Pickit2.

The work around to that, is to use a 40 pin chip, such as the 877A, dedicating these 3 pins to the debugger, once you code is fully tested, then reallocate your ports for the 876 chip.

hth

Richard

3v0 · Jul 24, 2008

The PICkit2 connects to the 16F876 on RB7/PGD, RB6/PGC, and MCLR/VPP.
Why are we talking about RB4 and RB5 ?

jay543_uk said:
hi all, iv started using a pickit2 clone and its working fine but the only problem is that it is connected to portb rb4 and rb5 on my 16f876a but for me to test my circuit proply i need to use these pins for an output at the same time as testing with the pickit2, can any one advise me if i can do this.

thanks jason

EDIT: Richard beat me to it.

Maybe post a schematic of what you want to do with portB.

jay543_uk · Jul 24, 2008

Ya Sorry, Just Check And You Are Right, I Have Got Them Connected To Rb7 And Rb6, But You'v Answered My Question That I Carnt Debug And Use The Same Ports As Output At The Same Time

Many Thanks

Jason

AtomSoft · Jul 24, 2008

correct Jason but i think you can still ICSP. Just use 2 diodes. This way data can only flow from pickit 2 to the pic and not from pic/circuit to the pickit 2

jay543_uk · Jul 25, 2008

well after playing around with my pickit2 and my asm code i got it working, its a 2x 8x8 led display which scrolls the time across it from a ds1337.I'm very happy with this as its my first fully working project with i2c and spi,the only problem is that i wanted more 8x8 led matrix to make a larger display.I changed my asm to have 6 matrixs but it doesnt work and am just getting a wierd thing happening in the xfer16 call.

what happens is nothing comes up on the displays and when you pause in debug it shows CNT to be holding A4 or a very high number but how can this happen if iv done "movlw 0x08, movwf CNT".

iv read that if you make calls across memory pages it can cause problems but is this what is happening to me, i dont really understand what is going on

HELP

thanks jason

Code:

	LIST	p=16F876a		;tell assembler what chip we are using
	include "P16F876a.inc"		;include the defaults for the chip
	ERRORLEVEL	0,	-302	;suppress bank selection messages
	__config 0x373a			;sets the configuration settings (oscillator type etc.)





		cblock	0x20			;start of general purpose registers
			
			OUT1 		;first byte to send out on spi
			OUT2		;second byte to send out on spi
			TMP1		;temp storage for spi
			CNT			;Count for byte for spi


			count			;used in looping routines
			count1			;used in delay routine
			counta			;used in delay routine
			countb			;used in delay routine
			tmp1			;temporary storage
			tmp2
			p_temp			;save register
			s_temp			;save register
			w_temp			;save register
						
						;registers for display

			row_pos			;position on row

			zero1			;zero storage
			one1		;one storage
			two1			;two storage
			three1			;three storage
			four1			;four storage
			five1			;five storage
			six1			;six storage
			seven1			;seven storage
			zero2			;zero storage
			one2		;one storage
			two2			;two storage
			three2			;three storage
			four2			;four storage
			five2			;five storage
			six2			;six storage
			seven2			;seven storage
			zero3			;zero storage
			one3		;one storage
			two3			;two storage
			three3			;three storage
			four3			;four storage
			five3			;five storage
			six3			;six storage
			seven3			;seven storage
			zero4			;zero storage
			one4		;one storage
			two4			;two storage
			three4			;three storage
			four4			;four storage
			five4			;five storage
			six4			;six storage
			seven4			;seven storage
			zero5
			one5		;one storage
			two5			;two storage
			three5			;three storage
			four5			;four storage
			five5			;five storage
			six5			;six storage
			seven5			;seven storage
			zero6
			one6		;one storage
			two6			;two storage
			three6			;three storage
			four6			;four storage
			five6			;five storage
			six6			;six storage
			seven6			;seven storage

			zerol			;zero storage
			onel			;one storage
			twol			;two storage
			threel			;three storage
			fourl			;four storage
			fivel			;five storage
			sixl			;six storage
			sevenl			;seven storage
			TEN				;CONVERT CLOCK RESULT TENS TO SINGLE UNIT
			UNITS			;CONVERT CLOCK	RESULT UNITS TO SINGLE UNIT
			TEMPCLOCK		;HOLDS TEMP CLOCK RESULT FOR TENSANDUNITS
			SCRATCH			; 1 by general-purpose scratchpad
			TMP				; temp register
			TMP2				; temp register
			COUNT		
			YRS		
			MON	
			DOW		
			DAYS		
			HRS		
			MINS		
			SEC	
		endc


CS EQU 0		;enable stobe
MOSI EQU 3		;output for spi from master
SPICLK EQU 2	;clock for spi

ROW_PORT	Equ	PORTB			;row port



	org	0x0000
	goto	START

;**************************************************************************	
;			     	Interrupt routine
;**************************************************************************



; 	Interrupt routine handles TMR2 which generates a 1ms tick

;	Interrupt vector

		ORG	0x0004
INT
		movwf	w_temp		; Save W register
		swapf	STATUS,W	; Swap status to be saved into W
		movwf	s_temp		; Save STATUS register
		movfw	PCLATH
		movwf	p_temp		; Save PCLATH 
	
		btfss	PIR1,TMR2IF	; Flag set if TMR2 interrupt
		goto	INTX		; Jump if not timed out

		; Timer (TMR2) timeout
	

		
		btfss	row_pos, 0	;check which ROW was last
		goto	Do_One
		btfss	row_pos, 1	;check which ROW was last
		goto	Do_Two
		btfss	row_pos, 2	;check which ROW was last
		goto	Do_Three
		btfss	row_pos, 3	;check which ROW was last
		goto	Do_Four
		btfss	row_pos, 4	;check which ROW was last
		goto	Do_Five
		btfss	row_pos, 5	;check which ROW was last
		goto	Do_Six
		btfss	row_pos, 6	;check which ROW was last
		goto	Do_Seven

Do_Zero		movlw	0xFF
		movwf	row_pos
		movf	zero1,	w
		MOVWF	OUT1
		MOVF	zero2,	w
		movwf	OUT2
		CALL	xfer16
		MOVF	zero3,	w
		movwf	OUT1
		MOVF	zero4,	w
		movwf	OUT2
		CALL	xfer16
		movf	zero5,	w
		movwf	OUT1
		movf	zero6,	w
		movwf	OUT2
		call	xfer16
		bcf	row_pos, 0
		call	DisplayOn
		bcf	ROW_PORT, 0	;turn ON row zero
		goto	INTX

Do_One		movlw	0xFF
		movwf	row_pos
		movf	one1,	w
		MOVWF	OUT1
		MOVF	one2,	w
		movwf	OUT2
		CALL	xfer16
		MOVF	one3,	w
		movwf	OUT1
		MOVF	one4,	w
		movwf	OUT2
		CALL	xfer16
		movf	one5,	w
		movwf	OUT1
		movf	one6,	w
		movwf	OUT2
		call	xfer16
		bcf	row_pos, 1
		call	DisplayOn
		bcf	ROW_PORT, 0	;turn ON row zero
		goto	INTX

Do_Two	movlw	0xFF
		movwf	row_pos
		movf	two1,	w
		MOVWF	OUT1
		MOVF	two2,	w
		movwf	OUT2
		CALL	xfer16
		MOVF	two3,	w
		movwf	OUT1
		MOVF	two4,	w
		movwf	OUT2
		CALL	xfer16
		movf	two5,	w
		movwf	OUT1
		movf	two6,	w
		movwf	OUT2
		call	xfer16
		bcf	row_pos, 2
		call	DisplayOn
		bcf	ROW_PORT, 0	;turn ON row zero
		goto	INTX

Do_Three	movlw	0xFF		
		movwf	row_pos
		movf	three1,	w
		MOVWF	OUT1
		MOVF	three2,	w
		movwf	OUT2
		CALL	xfer16
		MOVF	three3,	w
		movwf	OUT1
		MOVF	three4,	w
		movwf	OUT2
		CALL	xfer16
		movf	three5,	w
		movwf	OUT1
		movf	three6,	w
		movwf	OUT2
		call	xfer16
		bcf	row_pos, 3
		call	DisplayOn
		bcf	ROW_PORT, 0	;turn ON row zero
		goto	INTX

Do_Four		movlw	0xFF
		movwf	row_pos
		movf	four1,	w
		MOVWF	OUT1
		MOVF	four2,	w
		movwf	OUT2
		CALL	xfer16
		MOVF	four3,	w
		movwf	OUT1
		MOVF	four4,	w
		movwf	OUT2
		CALL	xfer16
		movf	four5,	w
		movwf	OUT1
		movf	four6,	w
		movwf	OUT2
		call	xfer16
		bcf	row_pos, 4
		call	DisplayOn
		bcf	ROW_PORT, 0	;turn ON row zero
		goto	INTX

Do_Five	movlw	0xFF
		movwf	row_pos
		movf	five1,	w
		MOVWF	OUT1
		MOVF	five2,	w
		movwf	OUT2
		CALL	xfer16
		MOVF	five3,	w
		movwf	OUT1
		MOVF	five4,	w
		movwf	OUT2
		CALL	xfer16
		movf	five5,	w
		movwf	OUT1
		movf	five6,	w
		movwf	OUT2
		call	xfer16
		bcf	row_pos, 5
		call	DisplayOn
		bcf	ROW_PORT, 0	;turn ON row zero
		goto	INTX

Do_Six		movlw	0xFF
		movwf	row_pos
		movf	six1,	w
		MOVWF	OUT1
		MOVF	six2,	w
		movwf	OUT2
		CALL	xfer16
		MOVF	six3,	w
		movwf	OUT1
		MOVF	six4,	w
		movwf	OUT2
		CALL	xfer16
		movf	six5,	w
		movwf	OUT1
		movf	six6,	w
		movwf	OUT2
		call	xfer16
		bcf	row_pos, 6
		call	DisplayOn
		bcf	ROW_PORT, 0	;turn ON row zero
		goto	INTX

Do_Seven	movlw	0xFF
		movwf	row_pos
		movf	seven1,	w
		MOVWF	OUT1
		MOVF	seven2,	w
		movwf	OUT2
		CALL	xfer16
		MOVF	seven3,	w
		movwf	OUT1
		MOVF	seven4,	w
		movwf	OUT2
		CALL	xfer16
		movf	seven5,	w
		movwf	OUT1
		movf	seven6,	w
		movwf	OUT2
		call	xfer16
		bcf	row_pos, 7
	call	DisplayOn
		bcf	ROW_PORT, 0	;turn ON row zero
		goto	INTX


INTX
		movfw	p_temp
		movwf	PCLATH		; Restore PCLATH
		swapf	s_temp,W
		movwf	STATUS		; Restore STATUS register - restores bank
		swapf	w_temp,F
		swapf	w_temp,W	; Restore W register
		bcf	PIR1,TMR2IF	; Clear the calling flag
		retfie




;program initialisation
START		
		
		
		BANKSEL ADCON1			;disable analogue inputs
		movlw 	0x06
		movwf 	ADCON1
		BANKSEL PORTA
		bsf 	STATUS,		RP0	;select bank 1
		movlw	b'00000000'		;Set port data directions, data output
		movwf	TRISA
		movwf	TRISB
		MOVWF	TRISC
		
		MOVLW	B'00000111'

		MOVWF	OPTION_REG
		bcf 	STATUS,		RP0	;select bank 0

		movlw	0x01
		movwf	row_pos

		call	Clear			;clear display registers

		;	Set up Timer 2.
	
		;movlw	b'01111110'		; Post scale /16, pre scale /16, TMR2 ON
		;uncomment previous line, and comment next line, to slow multiplexing speed
		;so you can see the multiplexing happening
		movlw	b'00000110'		; Post scale /4, pre scale /16, TMR2 ON
		movwf	T2CON

		bsf 	STATUS,		RP0	;select bank 1

		movlw	.249			; Set up comparator
		movwf	PR2
		
	;	bsf	PIE1,TMR2IE		; Enable TMR2 interrupt
	;	bcf 	STATUS,		RP0	;select bank 
	;	bsf	INTCON,PEIE		; Enable all peripheral interrupts
	;	bsf	INTCON,GIE		; Global interrupt enable
		
		
		
Main	

		bcf	INTCON,PEIE		; Enable all peripheral interrupts
		bcf	INTCON,GIE		; Global interrupt enable
	
		bsf 	STATUS,		RP0	;select bank 1
		bcf	PIE1,TMR2IE		; disable TMR2 interrupt
		
		bcf 	STATUS,		RP0	;select bank 0
		CALL	InitI2C
		
		call	RTC_brst_rd


		bsf 	STATUS,		RP0	;select bank 1
		bsf	PIE1,TMR2IE		; Enable TMR2 interrupt
		bcf 	STATUS,		RP0	;select bank 

		bsf	INTCON,PEIE		; Enable all peripheral interrupts
		bsf	INTCON,GIE		; Global interrupt enable
		
		
		MOVF	HRS,W
		CALL	TENSANDUNITS
		MOVF	TEN,W
		CALL	NUMBERTABLE
		CALL	ScrollL8
		MOVF	UNITS,W
		CALL	NUMBERTABLE
		CALL	ScrollL8

		CALL	DOUBLEDOT
		CALL	ScrollL8

		MOVF	MINS,W
		CALL	TENSANDUNITS
		MOVF	TEN,W
		CALL	NUMBERTABLE
		CALL	ScrollL8
		MOVF	UNITS,W
		CALL	NUMBERTABLE
		CALL	ScrollL8

		CALL	DOT
		CALL	ScrollL8
		
		MOVF	SEC,W
		CALL	TENSANDUNITS
		MOVF	TEN,W
		CALL	NUMBERTABLE
		CALL	ScrollL8
		MOVF	UNITS,W
		CALL	NUMBERTABLE
		CALL	ScrollL8
		CALL	Delay1Sec
		CALL	Clear


		goto	Main			;endless loop


;***********************************************************
;*****************start of subroutines**********************
;***********************************************************

TENSANDUNITS
	movwf	TEMPCLOCK
	andlw   b'00001111'
	movwf	UNITS
	swapf	TEMPCLOCK,w
	andlw	b'00001111'
	movwf	TEN
	RETURN
NUMBERTABLE
	ADDWF	PCL
		goto	Load_Zero
		goto 	Load_One
		goto 	Load_Two
		goto 	Load_Three
		goto 	Load_Four
		goto 	Load_Five
		goto 	Load_Six
		goto 	Load_Seven
		goto 	Load_Eight
		goto 	Load_Nine

Clear		clrf	zero1
			CLRF	zero2
			clrf	zero3
			CLRF	zero4
			clrf	zero5
			clrf	zero6


		clrf	one1
		clrf	one2
		clrf	one3
		clrf	one4
		clrf	one5
		clrf	one6

		clrf	two1
		clrf	two2
		clrf	two3
		clrf	two4
		clrf	two5
		clrf	two6

		clrf	three2
		clrf	three1
		clrf	three3
		clrf	three4
		clrf	three5
		clrf	three6

		clrf	four1
		clrf	four2
		clrf	four3
		clrf	four4
		clrf	four5
		clrf	four6

		clrf	five1
		clrf	five2
		clrf	five3
		clrf	five4
		clrf	five5
		clrf	five6

		clrf	six1
		clrf	six2
		clrf	six3
		clrf	six4
		clrf	six5
		clrf	six6

		clrf	seven1
		clrf	seven2
		clrf	seven3
		clrf	seven4
		clrf	seven5
		clrf	seven6
		RETURN

DOUBLEDOT
	movlw	0x00
		movwf	zerol
		movlw	0X18
		movwf	onel
		movlw	0x18
		movwf	twol
		movlw	0x00
		movwf	threel
		movlw	0x00
		movwf	fourl
		movlw	0x18
		movwf	fivel
		movlw	0x18
		movwf	sixl
		movlw	0x00
		movwf	sevenl
		
		return

DOT
	movlw	0x00
		movwf	zerol
		movlw	0X18
		movwf	onel
		movlw	0x18
		movwf	twol
		movlw	0x00
		movwf	threel
		movlw	0x00
		movwf	fourl
		movlw	0x00
		movwf	fivel
		movlw	0x00
		movwf	sixl
		movlw	0x00
		movwf	sevenl
		return



Load_Zero	movlw	0x00
		movwf	zerol
		movlw	0x38
		movwf	onel
		movlw	0x44
		movwf	twol
		movlw	0x4C
		movwf	threel
		movlw	0x54
		movwf	fourl
		movlw	0x64
		movwf	fivel
		movlw	0x44
		movwf	sixl
		movlw	0x38
		movwf	sevenl
		return

Load_One	movlw	0x00
		movwf	zerol
		movlw	0x38
		movwf	onel
		movlw	0x10
		movwf	twol
		movlw	0x10
		movwf	threel
		movlw	0x10
		movwf	fourl
		movlw	0x10
		movwf	fivel
		movlw	0x30
		movwf	sixl
		movlw	0x10
		movwf	sevenl
		return

Load_Two	movlw	0x00
		movwf	zerol
		movlw	0x7C
		movwf	onel
		movlw	0x20
		movwf	twol
		movlw	0x10
		movwf	threel
		movlw	0x08
		movwf	fourl
		movlw	0x04
		movwf	fivel
		movlw	0x44
		movwf	sixl
		movlw	0x38
		movwf	sevenl
	return

Load_Three	movlw	0x00
		movwf	zerol
		movlw	0x38
		movwf	onel
		movlw	0x44
		movwf	twol
		movlw	0x04
		movwf	threel
		movlw	0x08
		movwf	fourl
		movlw	0x10
		movwf	fivel
		movlw	0x08
		movwf	sixl
		movlw	0x7C
		movwf	sevenl
		
		return
Load_Four	movlw	0x00
		movwf	zerol
		movlw	0x08
		movwf	onel
		movlw	0x08
		movwf	twol
		movlw	0x7C
		movwf	threel
		movlw	0x48
		movwf	fourl
		movlw	0x28
		movwf	fivel
		movlw	0x18
		movwf	sixl
		movlw	0x08
		movwf	sevenl
	
		return

Load_Five	movlw	0x00
		movwf	zerol
		movlw	0x38
		movwf	onel
		movlw	0x44
		movwf	twol
		movlw	0x04
		movwf	threel
		movlw	0x04
		movwf	fourl
		movlw	0x78
		movwf	fivel
		movlw	0x40
		movwf	sixl
		movlw	0x7C
		movwf	sevenl
		
		return

Load_Six	movlw	0x00
		movwf	zerol
		movlw	0x38
		movwf	onel
		movlw	0x44
		movwf	twol
		movlw	0x44
		movwf	threel
		movlw	0x78
		movwf	fourl
		movlw	0x40
		movwf	fivel
		movlw	0x20
		movwf	sixl
		movlw	0x18
		movwf	sevenl
		
		return

Load_Seven	movlw	0x00
		movwf	zerol
		movlw	0x20
		movwf	onel
		movlw	0x20
		movwf	twol
		movlw	0x20
		movwf	threel
		movlw	0x10
		movwf	fourl
		movlw	0x08
		movwf	fivel
		movlw	0x04
		movwf	sixl
		movlw	0x7C
		movwf	sevenl
		
		return

Load_Eight	movlw	0x00
		movwf	zerol
		movlw	0x38
		movwf	onel
		movlw	0x44
		movwf	twol
		movlw	0x44
		movwf	threel
		movlw	0x38
		movwf	fourl
		movlw	0x44
		movwf	fivel
		movlw	0x44
		movwf	sixl
		movlw	0x38
		movwf	sevenl
	
		return

Load_Nine	movlw	0x00
		movwf	zerol
		movlw	0x30
		movwf	onel
		movlw	0x08
		movwf	twol
		movlw	0x04
		movwf	threel
		movlw	0x3C
		movwf	fourl
		movlw	0x44
		movwf	fivel
		movlw	0x44
		movwf	sixl
		movlw	0x38
		movwf	sevenl
	
		return


ScrollL8	call	ScrollL
		call	Delay50	
		call	ScrollL
		call	Delay50	
		call	ScrollL
		call	Delay50
		call	ScrollL
		call	Delay50	
		call	ScrollL
		call	Delay50	
		call	ScrollL
		call	Delay50	
		call	ScrollL
		call	Delay50	
		call	ScrollL
		call	Delay50
		return






ScrollL		bcf	STATUS, C
		rlf	zerol, f
		rlf	zero1, f
		rlf	zero2, f
		rlf	zero3, f
		rlf	zero4, f
		rlf	zero5, f
		rlf	zero6, f

		bcf	STATUS, C

		rlf	onel, f
		rlf	one1, f
		rlf	one2, f
		rlf	one3, f
		rlf	one4, f
		rlf	one5, f
		rlf	one6, f

		bcf	STATUS, C

		rlf	twol, f
		rlf	two1, f
		rlf	two2, f
		rlf	two3, f
		rlf	two4, f
		rlf	two5, f
		rlf	two6, f

		bcf	STATUS, C

		rlf	threel, f
		rlf	three1, f
		rlf	three2, f
		rlf	three3, f
		rlf three4, f
		rlf three5, f
		rlf	three6, f
		
		bcf	STATUS, C

		rlf	fourl, f
		rlf	four1, f
		rlf	four2, f
		rlf four3, f
		rlf	four4, f
		rlf	four5, f
		rlf	four6, f

		bcf	STATUS, C

		rlf	fivel, f
		rlf	five1, f
		rlf	five2, f
		rlf	five3, f
		rlf five4, f
		rlf five5, f
		rlf	five6, f

		bcf	STATUS, C

		rlf	sixl, f
		rlf	six1, f
		rlf	six2, f
		rlf	six3, f
		rlf six4, f
		rlf six5, f
		rlf	six6, f

		bcf	STATUS, C

		rlf	sevenl, f
		rlf	seven1, f
		rlf	seven2, f
		rlf	seven3, f
		rlf	seven4, f
		rlf	seven5, f
		rlf	seven6, f

		return

;***********************************************************
;***************DELAY ROUTINE*******************************
;***********************************************************



Delay1Sec	call	Delay250
		call	Delay250
		call	Delay250
		call	Delay250
		Return


Delay255	movlw	0xff	;delay 255mS
		goto	d0
Delay250	movlw	d'250'	;delay 250mS
		goto	d0
Delay100	movlw	d'100'	;delay 100mS
		goto	d0
Delay50		movlw	d'50'	;delay 50mS
		goto	d0
Delay20		movlw	d'20'	;delay 20mS
		goto	d0
Delay10		movlw	d'10'	;delay 10mS
		goto	d0
Delay1		movlw	d'1'	;delay 1mS
		goto	d0
Delay5		movlw	0x05	;delay 5ms
d0		movwf	count1
d1		movlw	0xE7
		movwf	counta
		movlw	0x04
		movwf	countb
Delay_0		decfsz	counta, f
		goto	$+2
		decfsz	countb, f
		goto	Delay_0
		decfsz	count1	,f
		goto	d1
		retlw	0x00


;-----------------------------------------
;--           RTC routines              --
;-----------------------------------------

RTC_brst_rd:
	call I2CSTART
	movlw	0D0h			; slave address + write
	call	I2CSEND
	movlw	0X00			; set word address to seconds register
	call	I2CSEND
	call 	I2CRESTART
	movlw	0D1h			; slave address + read
	call	I2CSEND
	call	I2CREAD		; read the seconds data
	movwf	SEC			; save it
	call	I2CACK
	call	I2CREAD		; and so on
	movwf	MINS
	call	I2CACK
	call	I2CREAD
	movwf	HRS
;	call	I2CACK
;	call	I2CREAD
;	movwf	DOW
;	call	I2CACK
;	call	I2CREAD
;	movwf	DAYS
;	call	I2CACK
;	call	I2CREAD
;	movwf	MON
;	call	I2CACK
;	call	I2CREAD
;	movwf	YRS
	CALL	I2CNACK
	CALL	I2CSTOP
	
	return

;-----------------------------------------
;--           I2C routines              --
;-----------------------------------------
InitI2C: ; The subroutine of I2C Initialization 
BANKSEL TRISC
movlw B'00011000' ; Initial PortC,bit 3 & 4 as Input
movwf TRISC ; RC3 = SCL , RC4 = SDA

BANKSEL PORTC
movlw 0xff
movwf PORTC

movlw .50 ; This gives 100KHz I2C clock @ 4MHz  (FOSC/CLOCKFREZ)/4 - 1 =BRG
banksel SSPADD
movwf SSPADD
movlw b'10000000' ; Disable slew rate control.
banksel SSPSTAT
movwf SSPSTAT
movlw b'00000000' ;
movwf SSPCON2 ; Setup MSSP for continuous reception.
movlw b'00101000' ; Enable MSSP and setup for I2C master
banksel SSPCON ; mode.
movwf SSPCON
banksel	PIR1
movlw	0x00
movwf	PIR1
return


I2CSTOP
	BANKSEL	SSPCON2
	bsf	SSPCON2, 2
	CALL	I2CWAIT
	BANKSEL 0
	RETURN

I2CWAIT
	banksel PIR1
FLoop btfss PIR1,SSPIF
	goto	FLoop
	bcf PIR1,SSPIF
return


I2CRESTART
	BANKSEL	SSPCON2
	BSF		SSPCON2,RSEN
	BCF		SSPCON2,ACKSTAT
	CALL	I2CWAIT
	BANKSEL	0
	RETURN

I2CSTART
	BANKSEL	SSPCON2
	BSF		SSPCON2,SEN
	CALL	I2CWAIT
	BANKSEL	0
	RETURN
	

I2CSEND
	BANKSEL	0
	MOVWF	SSPBUF
	CALL	I2CWAIT
	RETURN

I2CREAD
	BANKSEL	SSPCON2
	BSF		SSPCON2, 3
	CALL	I2CWAIT
	MOVF	SSPBUF, W
	BANKSEL	0
	RETURN

I2CACK
	BANKSEL	SSPCON2
	BSF		SSPCON2, ACKEN
	BCF		SSPCON2, ACKDT
	CALL	I2CWAIT	
	BANKSEL	0
	RETURN

I2CNACK
	BANKSEL	1
	BSF		SSPCON2, ACKEN
	BSF		SSPCON2, ACKDT
	BANKSEL	0
	RETURN
	

;I2CACKSTAT
;	BTFSC	SSPCON2, 6
;	GOTO ACKSTATERROR
;	RETLW 0


;*****************************************************
;***********	S.P.I	ROUTINE	**********************
;*****************************************************
xfer08:
	movf OUT1, 0		
	call xfer8			; send first byte
					; wait
	return


xfer16:
	movf OUT1, 0		
	call xfer8			; send first byte
	movf OUT2, 0
	call xfer8			; send second byte
					; wait
	return

xfer8:	movwf TMP1
	movlw 0x8
	movwf CNT

xfer1:	
	MOVLW	0X8
	MOVWF	CNT
RE	rlf TMP1, 1 ;rotate MSB of TMP1 into C
	bcf PORTA, MOSI	;clear output bit
	btfsc STATUS, C ;if rotated-out bit was high,
	bsf PORTA, MOSI ;output high bit
	nop				;keep time constant
	
	bsf PORTA, SPICLK	;bring clock high

	nop
	nop
	nop
	nop
	nop
	nop
	nop
	nop	;8x nop to make clock symmetric
	

	bcf PORTA, SPICLK
	; this would implement MISO, except that we don't need it.
;	bcf STATUS, C		;clear C
;	btfsc PORTB, MISO	;test MISO bit
;	bsf STATUS, C		;set C if MISO bit set
;	nop					;keep time constant
;	rlf TMP2, 1			;rotate carry into TMP2
	
	decfsz CNT, 1
;	goto xfer1
	GOTO RE
	return


DisplayOn
		BCf	PORTA,CS
		BSf	PORTA,CS
		RETLW 0


ISR



	END

richard.c · Jul 25, 2008

Hi Jason,

Bit difficult to go all the way through your code, but the thing that stands out straight away,is your use of calls, and so many of them, from within the ISR.

I was always told to keep the code in the ISR as short as possible and not to execute any calls out of the ISR routine.
Reasons get complicated , things like the progam couter stack etc -basically the progam can loose it way back from the ISR.

Try using the ISR to just reset your timer/s, update your timer variables, without using calls, and set some flags ( variables ) to on or off, so that when you go back into the main routine, you check those flags and act on them accordingly.

As for your memory page usage, your 8k word 876A chip does not need any special coding until you go over the 2k word boundary, which you can easily gauge from the disassembler listing or the prorammmer memory useage. doubt you code is bigger than 2k.

I started on the 873/6 chips, and have never regetted moving onto the 18F2520 chip which allows you to use all the program memory and 384 bytes of ram without need of page or bank coding.

hth

Richard

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