Post by thread:[PIC] I2C on PIC16F877 with ASM

List, I've finally got back around to a project which has been hanging around for a while using I2C. The aspect of the project I am having trouble with happens to be the heart of it, the I2C (would it be anything else???). Initially I figured I would try and get the PIC to control a single MAX7300 I2C GPIO. After going through many application notes, mpasm manuals and countless web pages describing very similar setups I felt comfortable it wouldnt be overly difficult. I've got a 16F877 on a board with 20Mhz Crystal, and an old ICD (and old version of MPLAB to match). It could be my assumptions in testing which are letting me down but I dont think im that lucky. I've tried various example codes off the net and written my own and have settled on this jigsaw as probably the best however it still doesnt work. When I run the code through I am expecting to see activity on the cro on either the SDA or SCL however see none, only a constant high caused by the pull up resisters. When I debug the code in MPLAB it seems to endlessly loop in the routine which checks the status of the bus (This one is directly copied from the application note) I2CWait. Can anyone with experiance in I2C see where I am going wrong?? Any help appriciated. LIST p=16F877 include "P16F877.INC" #define R_W_MASK 0x04 #define SSPIF_MASK 0x08 DELAYC EQU 32 org 0 goto start ;================================================== ;=Configure the MSSP as an I2C Port on a PIC16F877 = ;================================================== ConfigureI2C bsf SSPCON, SSPEN ;Enable I2C bsf SSPCON, SSPM3 ;Setup I2C bcf SSPCON, SSPM2 bcf SSPCON, SSPM1 bcf SSPCON, SSPM0 bsf STATUS, RP0 ;Register Page 1 movlw .0 movwf SSPCON2 bcf SSPSTAT, SMP bcf SSPSTAT, CKE ;Set I2C Levels ;Set I2C Speed movlw b'00001100' ;100k at 4Mhz Clock THIS NEEDS CHANGING movwf SSPADD bcf STATUS, RP0 ;Return to Page 0 ;================================================ ;================================================ ;=Send a Character via I2C = ;================================================ I2CSend movwf SSPBUF ;Load data to send call I2CWait ;Wait for completion return ;================================================ ;================================================ ;=Send an I2C ACK = ;================================================ I2CAck bsf STATUS, RP0 ;Page 1 bcf SSPCON2, ACKDT ;Setup for Ack bsf SSPCON2, ACKEN ;Send Ack bcf STATUS, RP0 ;Page 0 call I2CWait ;Wait for completion return ;================================================ ;================================================ ;=Send an I2C NAK = ;================================================ I2CNak bsf STATUS, RP0 ;Page 1 bcf SSPCON2, ACKDT ;Setup for NAK bsf SSPCON2, ACKEN ;Send NAK bcf STATUS, RP0 ;Page 0 call I2CWait ;Wait for completion return ;================================================ ;================================================ ;=Generate an I2C Start = ;================================================ I2CStart bsf STATUS, RP0 ;Page 1 bsf SSPCON2, SEN ;Initiate Start Condition bcf STATUS, RP0 ;Page 0 call I2CWait ;Wait for completion return ;================================================ ;================================================ ;=Generate an I2C Restart = ;================================================ I2CRestart bsf STATUS, RP0 ;Page 1 bsf SSPCON2, RSEN ;Initiate Restar Condition bcf STATUS, RP0 ;Page 0 call I2CWait ;Wait for completition return ;================================================ ;================================================ ;=Generate an I2C Stop = ;================================================ I2CStop bsf STATUS, RP0 ;Page 1 bsf SSPCON2, PEN ;Generate Stop bcf STATUS, RP0 ;Page 0 call I2CWait ;Wait for completion return ;================================================ ;================================================ ;=Waits for I2C Process to complete = ;================================================ I2CWait banksel SSPSTAT ; select SFR bank btfsc SSPSTAT,R_W ; transmit in progress? goto $-1 ; module busy so wait banksel SSPCON2 ; select SFR bank movf SSPCON2,w ; get copy of SSPCON2 andlw 0x1F ; mask out non-status btfss STATUS,Z ; test for zero state goto $-3 ; bus is busy test again return ; return ;================================================ start call ConfigureI2C call I2CStart movlw .255 call I2CSend call I2CStop goto start end

liam . wrote: > ;================================================ > ;=Waits for I2C Process to complete > = > ;================================================ > I2CWait > banksel SSPSTAT ; select SFR bank > btfsc SSPSTAT,R_W ; transmit in progress? > goto $-1 ; module busy so wait > banksel SSPCON2 ; select SFR bank > movf SSPCON2,w ; get copy of SSPCON2 > andlw 0x1F ; mask out non-status > btfss STATUS,Z ; test for zero state > goto $-3 ; bus is busy test again > return ; return > ;================================================ Usually I just test SSPIF (and clear it if set), it makes things simpler. Also, I think your BRG value might be too low, although I haven't made much sense from the specs. For my current project (10Mhz) the value specified in the datasheet (0x3F) works fine, but those values don't really make much sense to me. You might want to specify SSPADD higher, since usually slower I2C will not hurt. Also, I used a 16F877A (not the same, they have a slightly different MSSP, but that only affected me on SLAVE mode which I used in an adjacent 16F876, because the non-A versions do not feature receive clock stretching). Check your TRIS bits, the pins must be set as inputs. Your Nak routine is wrong too, you want to bsf ACKDT If you're interested, the relevant bits of my code are: ;===================================================== #define I2CBRG 0x3F #define INPADDR b'0100000' ; PCF8574 address ;===================================================== START bcf STATUS,IRP bcf STATUS,RP1 ; setup bank 1 stuff bsf STATUS,RP0 ; TRIS Setup movlw b'101111' movwf TRISA movlw b'00000000' movwf TRISB movlw b'11011000' ; <- note setting as inputs movwf TRISC movlw b'00000000' movwf TRISD movlw b'111' movwf TRISE ;===================================================== ; I2C Setup movlw (1<<SMP)|(0<<CKE) ; normal rate, no SMBUS movwf SSPSTAT movlw I2CBRG ; setup I2C Baud Rate Generator movwf SSPADD bcf STATUS,RP0 ; back to bank 0 movlw (1<<SSPEN) | b'1000' ; SSP ON, I2C Master mode movwf SSPCON clrf SSPCON2 ;===================================================== And this example for reading 8 input bits from a PCF8574 chip: ;===================================================== WAITSET MACRO REG,BIT ; wait for bit set btfss REG,BIT goto $-1 ENDM ;===================================================== bcf PIR1,SSPIF ; clear any previous interrupt bsf STATUS,RP0 bsf SSPCON2,SEN ; send I2C START bcf STATUS,RP0 WAITSET PIR1,SSPIF bcf PIR1,SSPIF movlw (INPADDR<<1)|1 ; send address, read mode movwf SSPBUF WAITSET PIR1,SSPIF bcf PIR1,SSPIF bsf STATUS,RP0 btfsc SSPCON2,ACKSTAT ; ACK received? goto IN_NAK ; Nope. Problem. bsf SSPCON2,RCEN ; OK, receive data bcf STATUS,RP0 WAITSET PIR1,SSPIF bcf PIR1,SSPIF movf SSPBUF,W ; get data movwf INPUT_VALUE bsf STATUS,RP0 bsf SSPCON2,ACKDT ; NAK (we do not want any more data) bsf SSPCON2,ACKEN ; send it bcf STATUS,RP0 WAITSET PIR1,SSPIF bcf PIR1,SSPIF goto IN_DONE ; all done, STOP IN_NAK bcf STATUS,RP0 ; put your error set-up here, but jump ; to / fall down to IN_DONE for I2C stop IN_DONE bsf STATUS,RP0 bsf SSPCON2,PEN ; send I2C STOP bcf STATUS,RP0 WAITSET PIR1,SSPIF bcf PIR1,SSPIF ; all done now ;===================================================== (writing is the same, but with the LSB of the address set to 0 and writing afterwards and checking for NAK, same as when sending the address) Regards, -- Hector Martin (.....hectorKILLspam@spam@marcansoft.com) Public Key: http://www.marcansoft.com/hector.asc

> > Usually I just test SSPIF (and clear it if set), it makes things simpler. I've changed my wait routine to this and strangely enough I get the same problem it seems to just hang and loop forever in this sub routine. {Quote hidden}> > Also, I think your BRG value might be too low, although I haven't made > much sense from the specs. For my current project (10Mhz) the value > specified in the datasheet (0x3F) works fine, but those values don't > really make much sense to me. You might want to specify SSPADD higher, > since usually slower I2C will not hurt. Also, I used a 16F877A (not > the same, they have a slightly different MSSP, but that only affected > me on SLAVE mode which I used in an adjacent 16F876, because the non-A > versions do not feature receive clock stretching). > > Check your TRIS bits, the pins must be set as inputs. Your Nak routine > is wrong too, you want to bsf ACKDT > Done... I've tried varrying the SSPADD value but got no where. At one point i thought I had it working but it was a loose lead causing the cro to jump around the place. One thing thats different tonight verse last night and I'm not sure why is as soon as I start the program bit 4 (SDA) is pulled low and stays that way. Just checking, is my test setup at the moment right? PIC 16F877 with 20Mhz crystal with caps. 47K pull up on MCLR 2K4 pull up on SDA, and SCL (RC4, RC3) 60Mhz CRO attached to both SDA and SCL in refference to ground. Liam

I tried the following code provided by Hector and still have the same problem. The program forever loops in the I2C wait. Considering that this code works for Hector (correct me if Im wrong) as well as the other code direct from application notes and websites and my own ideas all haveing the same problems I am shifting my focus to hardware. What size pull ups do other people use ?? At the moment I am testing using a CRO and have no slave I2C components on the bus, i was under the impression I should still see activity such as I2C start. liaaam {Quote hidden}> > ;===================================================== > #define I2CBRG 0x3F > #define INPADDR b'0100000' ; PCF8574 address > ;===================================================== > START > bcf STATUS,IRP > bcf STATUS,RP1 ; setup bank 1 stuff > bsf STATUS,RP0 > > ; TRIS Setup > movlw b'101111' > movwf TRISA > movlw b'00000000' > movwf TRISB > movlw b'11011000' ; <- note setting as inputs > movwf TRISC > movlw b'00000000' > movwf TRISD > movlw b'111' > movwf TRISE > ;===================================================== > ; I2C Setup > movlw (1<<SMP)|(0<<CKE) ; normal rate, no SMBUS > movwf SSPSTAT > > movlw I2CBRG ; setup I2C Baud Rate Generator > movwf SSPADD > > bcf STATUS,RP0 ; back to bank 0 > > movlw (1<<SSPEN) | b'1000' ; SSP ON, I2C Master mode > movwf SSPCON > > clrf SSPCON2 > ;===================================================== > > And this example for reading 8 input bits from a PCF8574 chip: > > ;===================================================== > WAITSET MACRO REG,BIT ; wait for bit set > btfss REG,BIT > goto $-1 > ENDM > > ;===================================================== > > bcf PIR1,SSPIF ; clear any previous interrupt > bsf STATUS,RP0 > bsf SSPCON2,SEN ; send I2C START > bcf STATUS,RP0 > WAITSET PIR1,SSPIF > bcf PIR1,SSPIF > > movlw (INPADDR<<1)|1 ; send address, read mode > movwf SSPBUF > WAITSET PIR1,SSPIF > bcf PIR1,SSPIF > > bsf STATUS,RP0 > btfsc SSPCON2,ACKSTAT ; ACK received? > goto IN_NAK ; Nope. Problem. > > bsf SSPCON2,RCEN ; OK, receive data > bcf STATUS,RP0 > WAITSET PIR1,SSPIF > bcf PIR1,SSPIF > movf SSPBUF,W ; get data > movwf INPUT_VALUE > > bsf STATUS,RP0 > bsf SSPCON2,ACKDT ; NAK (we do not want any more data) > bsf SSPCON2,ACKEN ; send it > bcf STATUS,RP0 > WAITSET PIR1,SSPIF > bcf PIR1,SSPIF > > goto IN_DONE ; all done, STOP > > IN_NAK bcf STATUS,RP0 > ; put your error set-up here, but jump > ; to / fall down to IN_DONE for I2C stop > > IN_DONE bsf STATUS,RP0 > bsf SSPCON2,PEN ; send I2C STOP > bcf STATUS,RP0 > WAITSET PIR1,SSPIF > bcf PIR1,SSPIF > > ; all done now > > ;===================================================== > > (writing is the same, but with the LSB of the address set to 0 and > writing afterwards and checking for NAK, same as when sending the address) > > Regards, > -- > Hector Martin (hectorKILLspammarcansoft.com) > Public Key: http://www.marcansoft.com/hector.asc > > -

liam . wrote: > I tried the following code provided by Hector and still have the same > problem. The program forever loops in the I2C wait. Considering that > this code works for Hector (correct me if Im wrong) as well as the > other code direct from application notes and websites and my own ideas > all haveing the same problems I am shifting my focus to hardware. > > What size pull ups do other people use ?? At the moment I am testing > using a CRO and have no slave I2C components on the bus, i was under > the impression I should still see activity such as I2C start. I'm using 10K successfully right now. I can't see where I2C hardware problems could cause hangups. If a device does not respond, you get a NACK for the address byte. A possible hangup could be a forced CLK line low, since that would stop the current transfer (clock stretching). SDA going low means the START bit is properly sent (SDA high-to-low transition while CLK high means START). I haven't tried the ICD, but I wouldn't trust it much when working with hardware comms. Can you check using some simple debugging (bringing some outputs high on certain code points or similar)? Does it hang on the check after setting SEN high, or does it hang after placing the slave address in SSPBUF? As an aside note, I just saw a bug in my code: I clear SSPCON2 while in bank 0 (which clears TMR2 instead). It is probably not the cause of the problem, but worth noting. -- Hector Martin (.....hectorKILLspam.....marcansoft.com) Public Key: http://www.marcansoft.com/hector.asc