I2C Slave with a PIC

[tacbanon]

Thank you for the code, and thanks in advance DT for your valuable time...looking forward for the end result(I wish and pray that things goes well). I've been reading about I2C on net, trying to understand and the applications that might be done(particularly on Master-(multi-Slave/Multi-master)) are very interesting...

Regards,
tacbanon

[Charles Linquis]

Although my slave example may not be as robust as AN734, I have systems running that have 14 slaves running. All 14 slaves are polled on 2 second intervals. The master uses bit-banging (I2CWrite). I have never had trouble with the code below. I have tested it with -
18F8723, 18F2221, 18F2321, 18F2523 and had excellent results.

'****************************************************************
'*  Name    : I2C slave                                         *
'*  Author  : Charles Linquist                                  *
'*  Notice  : Copyright (c) 2010 [select VIEW...EDITOR OPTIONS] *
'*          : All Rights Reserved                               *
'*  Date    : 10/20/2010                                        *
'*  Version : 1.0                                               *
'*  Notes   : Transmits 100 bytes in ~14 ms (Master SEND)       *
'*          : Recives 100 bytes in ~12 ms (Master RECEIVE)      *  
'*          : Could possibly go faster.  Master used for  the   *
'*          : test used bit-banging (I2CREAD/I2CWRITE           *
'*          : settings on that end were                         *
'*          :  DEFINE I2C_SLOW 1 ,DEFINE I2C_HOLD 1             * 
'****************************************************************
ASM
    ifndef __18F2221
        error "18F2221 not selected"
    endif
ENDASM 
       
ASM
       movlw 0x62                              ; %0110 0010  = 4 Mhz, internal osc block
       movwf OSCCON
       movlw 0x80                              ; %1000 0000  = PLL disabled
       movwf OSCTUNE
ENDASM       
    
           
        DATA @0,0      ; programming flag
                      
        DEFINE OSC 4                                                          
        DEFINE NO_CLRWDT 1                                                      ' Don't waste cycles clearing WDT  
        Define USE_LFSR 1
        define USE_LOWPRIORITY 1
;---------------- Alias the bits ------------------------------------
    
    SSPIF               VAR PIR1.3    ' SSP (I2C) interrupt flag
    SSPIE               VAR PIE1.3    ' Int Enable
   
    SSPUA               VAR SSPSTAT.1
    SSPS                VAR SSPSTAT.3
    SSPP                VAR SSPSTAT.4
    SSPSMP              VAR SSPSTAT.7
    
    BF                  VAR SSPSTAT.0 ' SSP (I2C) Buffer Full
    R_W                 VAR SSPSTAT.2 ' SSP (I2C) Read/Write
    D_A                 VAR SSPSTAT.5 ' SSP (I2C) Data/Address
    CKP                 VAR SSPCON1.4  ' SSP (I2C) SCK Release Control
    SSPEN               VAR SSPCON1.5  ' SSP (I2C) Enable
    SSPOV               VAR SSPCON1.6  ' SSP (I2C) Receive Overflow Indicator
    WCOL                VAR SSPCON1.7  ' SSP (I2C) Write Collision Detect
    GENCALL             VAR SSPCON2.7  ' General Call enabled
    
    MainTimer           var word bankA System
    I2CTimer            var word bankA System
    I2CTimerGate        var byte bankA System
    I2CErr              var byte bankA System
;-------------------------------------------------------------------------  
;Alias pins
    SCL     VAR     PORTC.3         ' I2C clock input
    SDA     VAR     PORTC.4         ' I2C data input
    LED     VAR     PORTB.5
    
 
'------------------- Rx Buffer defintion --------------------
    RxBufferLEN         con 10         
    RxBuffer            var BYTE[Rxbufferlen + 1]    
    TxBufferLEN         CON 10
    TXBuffer            VAR BYTE[TxBufferLEN + 2]
    InBuff              VAR BYTE
   
    GeneralCall         VAR BIT
    RXBufferOverFlow    VAR BIT
    TxBufferUnderFlow   VAR BIT
    RXBufferPointer     VAR Byte
    TXBufferPointer     VAR Byte
    address             VAR BYTE
    x                   VAR BYTE
    dummy               var byte
    I2CAddress          VAR BYTE
    WCOLCounter         VAR BYTE
;-------------------------------------------------------------    
    TXBuffer[TxBufferLen + 1] = $FF  ; Char to send if requestor asks for too much.
    
    I2CDeviceAddress    VAR BYTE
    
    I2CMajorAddress     CON $3
    I2CDeviceAddress =  $8   
     
    I2CAddress = (I2CMajorAddress <<4) | I2CDeviceAddress 
;---------------------------------------------------------------       
    SSPADD = I2Caddress ' Set our address
    SSPCON2.0 = 1      ; Stretch the clock
    SSPSTAT = 0
    SSPEN = 1             
    SSPIE = 1 
    SSPIF = 0 
    GenCall = 1           ; Turn general call on
    SSPCON2.7 = 1         ' General call address ENABLED
    SSPCON1 = $36    ' Set to I2C slave with 7-bit address    
       
;---------------------------------------------------------------
    TRISA = %11111111
    TRISB = %11011111
    TRISC = %11111111
       
' -------------- Turn on Ints  ------------------------
    INTCON.7 = 1  ; global ints
    INTCON.6 = 1  ; peripheral ints
   
;------------------  Clear parameters --------------
    RXBufferPointer = 0
    TxBufferPointer = 0
    GeneralCall = 0 
    RxBufferOverFlow = 0
    TXBufferUnderFlow = 0
    WCOLCounter = 0
;---------------------------------------------------------------------  
   
INCLUDE "DT_INTS-18.bas"    ' Base Interrupt System
INCLUDE "ReEnterPBP-18.bas"     ' Use PBP interrupts
include "ReEnterPBP-18LP.bas"
ASM
INT_LIST  macro    ; IntSource,         Label,  Type, ResetFlag?
        INT_Handler    TMR0_INT, TimerInt,    ASM,  yes
       
    endm
    INT_CREATE               ; Creates the interrupt processor
    
INT_LIST_L  macro    ; IntSource,        Label,  Type, ResetFlag?
     INT_Handler    SSP_INT,  _I2C_Int,   PBP,  yes
     endm
     INT_CREATE_L               ; Creates the LP interrupt processor    
    
    
endasm
''----------------- Initialization Done! -----------------------------
    Goto OverInt ; jump over ISR

asm
TimerInt
      
      infsnz MainTimer
      incf   MainTimer + 1
      btfsc  I2CTimerGate,0        ; Don't count if low bit is clr
      incf   I2CTimer
      btfss  I2CTimer,2            ; Bit 2 is set , we have at least 4 counts, we must be hung
      bra    NoProb
      bcf    PIR1,3                ; Clear Int flag
      bcf    SSPCON1,5             ; Stop the 
      bsf    SSPCON1,5
      bsf    I2CErr,0
      clrf   I2CTimer
NoProb      
      bcf INTCON,2
            
      INT_RETURN
endasm
'------------------------- I2C subroutine  -------------------------------- 
I2C_Int:
  ; We don't get here uless someone has matched our address register.
@ bsf I2CTimerGate,0    ; start the counter
If R_W = 0 then             'This is a WRITE by the master to us
    IF BF = 0 Then goto i2CEXIT   ; Nothing for us!
    if D_A = 0 then         'We have an address
      address = SSPBUF     'Need to READ to satisfy Microchip
       IF Address = 0 THEN
           GeneralCall = 1
       ELSE
           GeneralCall = 0      
       ENDIF
           
    else            
        IF WCOL OR SSPOV THEN I2CExit
       
          RXBuffer [RxBufferPointer] = SSPBuf   ; 
          RxBufferPointer = RXBufferPointer + 1
           
          IF RXBufferPointer > RxBufferLen  THEN
                RXBufferOverFlow = 1
                RXBufferPointer = 0
          ENDIF 
              
        ENDIF
          
          
    else   ' R_W = 1 Master wants to read FROM us
          IF !D_A Then                          
                TxBufferPointer = 0  ' Mark as first read
                RXBufferPointer = 0
          EndIF
        
          IF CKP THEN I2CExit
              dummy = SSPBUF  ;NECESSARY!
          
          If TXBufferPointer < TxbufferLen THEN
SENDI2C:
              WCOL = 0
                  SSPBUF = TXBuffer[TXBufferPointer] ' Get data from array
                   IF WCOL THEN 
                       WCOLCounter = WCOLCounter + 1            ; Don't hang the bus with infinite WRITES!
                       IF WColCounter = 0 Then goto I2CExit     ; Rolled over
                      Goto SendI2C       ; Rety
                    ELSE
                       WColCounter = 0
                    ENDIF   
                   TXBufferPointer = TXBufferPointer +1
                   TXBufferPointer  = TXBufferPointer MIN TXBufferLen + 1 ; Don't let it get larger than this
                   ; Send FFs if requestor asks for too much data  
              ELSE
                  TXBufferPointer = 0
                  TXBufferUnderflow = 1
          ENDIF 
    ENDIF
          
I2CEXIT:
Asm
    bcf SSPCON1,6
    bcf SSPSTAT,0 
    bcf PIR1,3
    bsf SSPCON1,4
    
    bcf I2CTimerGate,0      ; stop the counter    
    INT_ENABLE SSP_INT      ; probably don't need this, but want to make certain it gets reenabled
    INT_RETURN
endasm
' -------------------------end I2C subroutine  -------------------------------- 
'--------------------[ main program loop]---------------------------------------
OverInt:
Asm
   clrf MainTimer
   clrf I2CTimer      
   bcf INTCON,2 
   bcf PIR1,3  ; Clear the I2C flag before we turn on the INT.
   movlw 0x83
   movf T0CON
   INT_ENABLE  SSP_INT     
   INT_ENABLE TMR0_INT
endasm



MAIN PROGRAM LOOP GOES HERE!

[tacbanon]

Hi Charles, thanks for sharing..I will try it out..


tacbanon

[tacbanon]

@Charles
Sorry I was not able to make it work on my setup..I'm not really sure what the following code is doing, so I tried to comment it and assign a value, but no effect.

I2CMajorAddress     CON $3
I2CDeviceAddress =  $8     
'I2CAddress = (I2CMajorAddress <<4) | I2CDeviceAddress 
I2CAddress =$14

I hope it will be alright if you share the master side code?

Thanks,
tacbanon

[Darrel Taylor]

At this point, I'm thinking Al (aratti) was right.

AN734 didn't work either.
Bytes are being put in the SSPBUF without an address match.
So the slaves that aren't being accessed are overflowing during reads from other devices.

The code I gave earlier works because it's resetting the overflow in the main loop, but that's just not right.

I'm trying to get some more info from Labcenter.

[Charles Linquis]

I am using a slight variant of the code I posted, and it is working fine. The only major change is that I'm sending a packet length byte, and I'm handling the entire receive packet inside the ISR. This is safe because I have my ( higher priority) timer interrupt watching over the whole process.

[tacbanon]

Hi,
Just want to ask if anyone tried to extend say 50meters communication between master and slave using I2C bus extender P82B715PN or similar?

Regards,
tacbanon