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I2c Problem On 16f876a

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J

jay543_uk

New Member
Hi All, Iv Been Looking At Nigels Tutorials And Iv Managed To Mod His Led Matrix Code To Display A Scrolling Clock Across 2 8x8 Led Matrix Using Two 74hc595n By Spi But The Only Problem Is I Carnt Get The I2c Part To Work To The Ds1337 Rtc.
At The Moment Nothing Works But If I Comment Out The Call To Rtc_burst_rd It Scrolls Zeros Across The Matrix.

The Code Is Abit Messy As Its Alot Of Stuff Iv Found On The Net And Pasted But I Just Carnt Get The I2c Side To Work.

I Thinks Its Got Something To Do With The I2cwait After The I2c Start Call

Thanks For Any Help

Regards Jason
 
Code: 
	LIST	p=16F876		;tell assembler what chip we are using
	include "P16F876.inc"		;include the defaults for the chip
	ERRORLEVEL	0,	-302	;suppress bank selection messages
	__config 0x393A			;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

			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

#define	SCL	PORTA,1		; bus clock line
#define	SDA	PORTA,4		; bus data line

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_PORT	;turn off all rows
		movwf	row_pos
		movf	zero1,	w
		MOVWF	OUT1
		MOVF	zero2,	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_PORT	;turn off all rows
		movwf	row_pos
		movf	one1,	w
		MOVWF	OUT1
		MOVF	one2,	w
		movwf	OUT2
		CALL	xfer16
		bcf	row_pos, 1
		call	DisplayOn
		bcf	ROW_PORT, 1	;turn ON row one
		goto	INTX

Do_Two		movlw	0xFF	
		movwf	ROW_PORT	;turn off all rows	
		movwf	row_pos
		movf	two1,	w
		MOVWF	OUT1
		MOVF	two2,	w
		movwf	OUT2
		CALL	xfer16
		bcf	row_pos, 2
		call	DisplayOn
		bcf	ROW_PORT, 2	;turn ON row one
		goto	INTX

Do_Three	movlw	0xFF
		movwf	ROW_PORT	;turn off all rows		
	movwf	row_pos
		movf	three1,	w
		MOVWF	OUT1
		MOVF	three2,	w
		movwf	OUT2
		CALL	xfer16
		bcf	row_pos, 3
		call	DisplayOn
		bcf	ROW_PORT, 3	;turn ON row one
		goto	INTX

Do_Four		movlw	0xFF
		movwf	ROW_PORT	;turn off all rows		
		movwf	row_pos
		movf	four1,	w
		MOVWF	OUT1
		MOVF	four2,	w
		movwf	OUT2
		CALL	xfer16
		bcf	row_pos, 4
		call	DisplayOn
		bcf	ROW_PORT, 4	;turn ON row one
		goto	INTX

Do_Five		movlw	0xFF		
		movwf	ROW_PORT	;turn off all rows
		movwf	row_pos
		movf	five1,	w
		MOVWF	OUT1
		MOVF	five2,	w
		movwf	OUT2
		CALL	xfer16
		bcf	row_pos, 5
		call	DisplayOn
		bcf	ROW_PORT, 5	;turn ON row one
		goto	INTX

Do_Six		movlw	0xFF		
		movwf	ROW_PORT	;turn off all rows
		movwf	row_pos
		movf	six1,	w
		MOVWF	OUT1
		MOVF	six2,	w
		movwf	OUT2
		CALL	xfer16
		bcf	row_pos, 6
		call	DisplayOn
		bcf	ROW_PORT, 6	;turn ON row one
		goto	INTX

Do_Seven	movlw	0xFF
		movwf	ROW_PORT	;turn off all rows		
		movwf	row_pos
		movf	seven1,	w
		MOVWF	OUT1
		MOVF	seven2,	w
		movwf	OUT2
		CALL	xfer16
		bcf	row_pos, 7
		call	DisplayOn
		bcf	ROW_PORT, 7	;turn ON row one
		
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
		
		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
		
*************;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 .49 ; This gives 100KHz I2C clock @ 20MHZ
	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
		
		
		
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	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			;clear display storage
		clrf	one1
		clrf	one2
		clrf	two1
		clrf	three2
		clrf	three1
		clrf	four1
		clrf	four2
		clrf	five1
		clrf	five2
		clrf	six1
		clrf	six2
		clrf	seven1
		clrf	seven2
		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
		bcf	STATUS, C
		rlf	onel, f
		rlf	one1, f
		rlf	one2, f
		bcf	STATUS, C
		rlf	twol, f
		rlf	two1, f
		rlf	two2, f
		bcf	STATUS, C
		rlf	threel, f
		rlf	three1, f
		rlf	three2, f
		bcf	STATUS, C
		rlf	fourl, f
		rlf	four1, f
		rlf	four2, f
		bcf	STATUS, C
		rlf	fivel, f
		rlf	five1, f
		rlf	five2, f
		bcf	STATUS, C
		rlf	sixl, f
		rlf	six1, f
		rlf	six2, f
		bcf	STATUS, C
		rlf	sevenl, f
		rlf	seven1, f
		rlf	seven2, 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
	return

;-----------------------------------------
;--           I2C routines              --
;-----------------------------------------




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


I2CRESTART
	BANKSEL	1
	BSF		SSPCON2,RSEN
	CALL	I2CWAIT
	BANKSEL	0
	RETURN

I2CSTART
	BANKSEL	1
	BSF		SSPCON2,0
	CALL	I2CWAIT
	BANKSEL	0
	RETURN
	

I2CSEND
	BANKSEL	0
	MOVWF	SSPBUF
	CALL	I2CWAIT
	RETURN

I2CREAD
	BANKSEL	1
	BSF		SSPCON2, 3
	CALL	I2CWAIT
	MOVF	SSPBUF, W
	BANKSEL	0
	RETURN

I2CACK
	BANKSEL	1
	BCF		SSPCON2, ACKDT
	BSF		SSPCON2, ACKEN
	BANKSEL	0
	RETURN

I2CNACK
	BANKSEL	1
	BSF		SSPCON2, ACKDT
	BSF		SSPCON2, ACKEN
	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:	
	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
	return


DisplayOn
		BCf	PORTA,CS
		BSf	PORTA,CS
		RETLW 0





	END
 
That code uses the hardware MSSP for I²C and so SDA and SCL have to be on RC3 and RC4. You have them on PORTA which will not work.

Mike.
 
hi mike,
forgot to delect the #define for scl and sca which i was using at first with some code for i2c for pics with out the mssp, I2c worked with that code but doesnt work with the mssp

my i2c lines are connected to rc3 and rc4

many thanks for any help

jason
 
BANKSEL TRISC
movlw B'00011000' ; Initial PortC,bit 3 & 4 as Input
movwf TRISC ; RC3 = SCL , RC4 = SDA
Click to expand...

i noticed iv made the scl and sda lines as inputs, is this right or should they be outputs

jason
 
jay543_uk said:
i noticed iv made the scl and sda lines as inputs, is this right or should they be outputs

jason
Click to expand...

That is correct both should be set as input for the MSSP module to work correctly.

I looked through your code and I can't see anything wrong. However, one thing to be aware of when developing I²C is that the bus can become stalled. If the pic is reset or otherwise interrupted whilst in the middle of an I²C transfer the bus can end up in an inconsistent state. A way to avoid this is to power the target circuit down between tests.

Another way is to manually clock the bus prior to enabling the hardware I²C. This is how I get around the problem on a 16F886,
Code: 
I2cInit		bsf	STATUS,RP0	;1
		bsf	TRISC,3
		bsf	TRISC,4
		bcf	STATUS,RP0
ClockLoop	btfsc	PORTC,4
		goto	BusFixed
		bcf	PORTC,3
		bsf	STATUS,RP0
		bcf	TRISC,3
		goto	$+1
		bsf	TRISC,3
		bcf	STATUS,RP0
		goto	ClockLoop

BusFixed
		bsf	STATUS,RP0
		movlw	.20000/4/.400
		movwf	SSPADD
		clrf	SSPSTAT
		bsf	SSPSTAT,SMP
		bcf	STATUS,RP0	;0
		movlw	0x28
		movwf	SSPCON
		bcf	PIR1,SSPIF
		bcf	PIR2,BCLIF
		return

Mike.
 
thanks for checking my code mike, i think ill pull my circuuit apart and build it back up again and see what happens, must be a hardware fault if the software is right.
The code you wrote, is that just executed on the pic start up or each time b4 you use the i2c interface, Does it not just keep doing a loop back to clockloop???

I am very new to this so sorry if this is stupid.

once i get the i2c working is there any way i could use the spi on portc3 & 4 pins as well and free up the porta pins im using to connect to the 74hc595n's

many thanks

jason
 
Iv just tryed to check my circuit and it all seems ok but i have rigged up to led onto portc3 and 4, both stay high and seem never to go low.To me its like the start condition is never being setup on sda and scl lines. should i put a delay in after the initialisation and before the i2c call to let the mssp setup.

running out of ideas




jason
 
Maybe I am missing something here. I just looked at the DS1337 data sheet. It expects SCL as an input. If the PIC is set for SCL as input, then who supplies the clock?
 
One of the devices has to be set to send clock, the other to receive clock. My question is which device will provide clock if both are inputs?
 
Mikebits said:
One of the devices has to be set to send clock, the other to receive clock. My question is which device will provide clock if both are inputs?
Click to expand...

You have to set the pic pins to input so they don't fight with the MSSP module. The module then switches the pics to in/out as required.

Mike.
 
Fair enough. I am not familiar with a mssp module. I was just wondering who supplied clock, now I know.

Thanks
 
jay543_uk said:
are is right.
The code you wrote, is that just executed on the pic start up or each time b4 you use the i2c interface, Does it not just keep doing a loop back to clockloop???
Click to expand...

The code checks the SDA line and if it is low then one of the other devices is sending data. When it finds this condition it pulses the SCL line until the SDA line becomes high. Edit, yes, it is just executed on startup.

If you have a ICD2 or Pickit2 then you can single step through the I²C routines and see where it is going wrong. If you set a breakpoint on the start of RTC_brst_rd, you can single step from there. Also when it stops check the values in the registers are what you expect I.E. SSPCON=0x28 TRICC3/4 are input etc.

Mike.
 
Last edited:
Iv Not Got A Debbuger Yet As Iv Not Long Started Playing Around With Pics,all I Have Is A Velleman Programmer And A Handful Of 16f876a Pics And A Book, Making The Rest Up As I Go Along.

What Debugger Would Be Best To Buy, Must Be Cheap


Jason
 
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