I2C Slave with a PIC

[DanPBP]

Try this code, I cleaned it up a lot. Slave address is 2.

1) From the master, try to read 12 from the slave

2) Try to send one byte (zero) to the slave and do something.

I don't have MPASM so, it could be some small errors, check them.

'Oscillator Initialization
DEFINE OSC 32 ' Osc. in MHz
OSCCON = %01110000 
OSCTUNE.6 = 1 
ADCON0.0 = 0 ' Turns off A-to-D module
ADCON1 = $0F ' Makes 100% port A digital 
TRISA = %00000000
CMCON = 7 ' Comparators Off

DEFINE I2C_HOLD 1

' Define used register flags
SSPIF VAR PIR1.3 ' SSP (I2C) interrupt flag
SSPIE VAR PIE1.3 ' SSP Int Enable
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
'STRETCH VAR SSPCON2.0 ' SSP (I2C) Clock stretch

'---------------- Alias pins -----------------------------------

TRISC.3 = 1 ' input
TRISC.4 = 1 ' input

'--------------- Define used register flags -------------------

STAT_BF VAR SSPSTAT.0 ' SSP (I2C) Buffer Full
STAT_RW VAR SSPSTAT.2 ' SSP (I2C) Read/Write
STAT_DA VAR SSPSTAT.5 ' SSP (I2C) Data/Address
CKE VAR SSPSTAT.6 ' SSP (I2C) Data/Address

'------------------- Rx Buffer definition --------------------
RxBufferLEN CON 1
RxBuffer VAR BYTE[Rxbufferlen]
RxBufferIndex VAR BYTE

'------------------ Tx Buffer definition ----------------------
TxBufferLEN CON 1
TxBuffer VAR BYTE[txbufferlen]
TxBufferIndex VAR BYTE

'------------------ Define constants ------------------------

I2Caddress CON $2 ' Make address = 2

' Define constants


datain VAR BYTE
readcnt VAR BYTE 
WRData VAR BYTE


'SSPADD = My_I2C_address ' Set our address
SSPADD = I2Caddress ' Set our address
SSPCON2.7 = 0 ' General call address disabled
SSPCON1 = $36 ' Set to I2C slave with 7-bit address
SSPSTAT = 0
SSPIE = 1 
SSPIF = 0 
RxBufferIndex = 0
TxBufferIndex = 0
bf = 0
SSPOV = 0

'Port C harware UART settings 
DEFINE HSER_RCSTA 90h 
DEFINE HSER_TXSTA 20h 
DEFINE HSER_BAUD 9600 
DEFINE HSER_CLROERR 1 

'----------------- Initialization Done! -----------------------------
GoTo main

'-------------------------------------------------------------------------------

I2C_Slave: ' I2C slave subroutine
          sspif = 0                            ' clear interrupt flag
          IF r_w = 1 Then I2C_Read                ' read data from us
          IF bf = 0 Then I2C_Exit               ' nothing in buffer so exit
          IF d_a = 1 Then I2C_Write                ' data for us (not address)
          IF sspbuf != i2caddress Then I2C_Exit ' clear the address from the buffer
          readcnt = 0                          ' mark as first read

          GoTo I2C_Exit

'-------------------------------------------------------------------------------

I2C_Write: ' I2C write data to us
       datain = sspbuf                   ' put buffer data into array
       rxbuffer[rxbufferindex] = datain
       rxbufferindex=rxbufferindex + 1

       IF rxbufferindex = rxbufferlen Then ' end of buffer transfer 
          wrdata = 1
          rxbufferindex = 0
       EndIF

GoTo i2c_exit

'-------------------------------------------------------------------------------
I2C_Read: ' I2C read data from us

       IF d_a = 0 Then
          txbufferindex = 0
       EndIF

       While stat_bf : Wend                        ' koop while buffer is full

       wcol = 0                                    ' clear collision flag
       sspbuf = txbuffer[txbufferindex]

       While wcol 
             wcol = 0
             sspbuf = txbuffer[txbufferindex]
       Wend

       ckp = 1                                     ' release clock, allowing read by master
       txbufferindex = txbufferindex + 1           ' increment index

       IF txbufferindex = txbufferlen Then         ' all bytes have been tx
          txbufferindex = 0                        ' reset index            
       EndIF

GoTo i2c_exit


'-------------------------------------------------------------------------------

I2C_Exit:
         sspov = 0
         wcol = 0
         wrdata = 0
Return

'-------------------------------------------------------------------------------

'-------------------------------------------------------------------------------
main:
      txbuffer[0] = 12 ' test value

      rxbuffer[0] = 0

      IF sspif = 1 Then
         GoSub i2c_slave
      EndIF

      Select Case rxbuffer[0]
             Case 0
                   ' do something here, turn on LED for example.
      End Select

      GoTo main

End

[BigWumpus]

You have to set the CKP-bit even after a WRITE-operation.
Try to disable the HSEROUT-lines.
Maybe this command will alter the TRISC-register, which will kill the I2C-engine.
Sometime, you should clear the OV-bit...

[DaveC3]

I have been trying to get a 18F2620 to run as a slave. i ran across this in the ERRATA for this device.

43. Module: MSSP (I2C Slave)
The MSSP module operating in I2C, 7-Bit Slave
mode (SSPM3:SSPM0 = 0110) may not send a
NACK bit (/ACK) in response to receiving the slave
address loaded in SSPADD<7:1>. Addresses are
in one of these ranges:
• 0x00 to 0x07
• 0x78 to 0x7F
These addresses were reserved by Philips® Semiconductors
in “The I2C Specification”, Version 2.1,
released January 2000. Section 10.1 “Definition of
bits in the first byte” defines the purposes of these
addresses.
This specification can be found at:
http://www.semiconductors.philips.com/i2c
Work around
This version of the silicon does not respond to
slave addresses in the ranges previously listed.
Use either of these work arounds:
• Change the 7-bit slave address in SSPADD to
an address in the range of 0x08 to 0x77.
• Use Revision B silicon. This version of silicon
removes this issue’s addressing restrictions.

I have gotten sporadic results for the master reading the slave in the following code.

Darrell's Instant Interrupt

    '   Interrupt definition   
    '   ====================
        '   USB interrupt used to keep USB connection alive
INCLUDE "DT_INTS-18.bas"    ' Base Interrupt System
INCLUDE "ReEnterPBP-18.bas"     ' Include if using PBP interrupts

ASM
INT_LIST  macro    ; IntSource,         Label,  Type, ResetFlag?
        INT_Handler    SSP_INT,  _I2C_Int,   PBP,  yes

    endm
    INT_CREATE               ; Creates the interrupt processor
endasm

''----------------- Initialization Done! -----------------------------

@ INT_ENABLE  SSP_INT     ; Master Synchronous Serial Port Interrupt Flag bit. The transmission/reception is complete
'txbuffer = 0

The Interrupt handler

I2C_Int:
If R_W = 0 then
    if D_A = 0 then
       address = SSPBUF
    else

Still working on master to slave write
'        if bf = 1 then
'           if rxcnt <= rxbufferlen then
'              datain[rxcnt] = SSPBUF
'              rxcnt = rxcnt + 1
'              if rxcnt = rxbufferlen then rxcnt = 0
'           endif   
          
          
        EndIF 
    endif
else
    dataout = SSPBUF     'dummy read
    if txcnt > 0 then
       SSPBUF = txbuffer[txoutptr]
       txoutptr = txoutptr + 1       
              if txoutptr = txbufferlen then txoutptr = 0
       txcnt = txcnt - 1
    else
    'no byte to send
    endif       
endif
CKP = 1 
@ INT_RETURN

and the main loop. I want to send three bytes to the master. In this case "three sevens".

Main:
SSPOV = 0
WCOL = 0
     
     if txcnt < txbufferlen - 1 then
                    
            TxBuffer[txinptr] = 7
            txinptr = txinptr + 1
            if txinptr = txbufferlen then txinptr = 0
           
            txcnt = txcnt + 1
            
    endif

WrData=0 



goto main 
end

I did the same slave program in "C" and it works well.

The Master is reading and writing to a RTC module and a bank of 4 24lc256 EEProms and a I2C Port expander with out any problems.

It is getting close

Take care

Dave

[rswain]

Although the 16F guys have been having good luck with low addresses, it makes sense that the errata sheet would point out the old Phillips rule about low addresses. I haven't tried an address above $08 before... gotta go give that a shot too. I'll report back with any results, good or bad.

Rswain

[rswain]

Today I tried changing the Master and Slave addresses to higher numbers. I tried $26, $A6, and $02 just for good measure. They all responded with the same results; the slave sees the address, matches to its own, sets the interrupt flag, sets the Buffer Full flag, loads the address byte into the SSPBUF and I can read it from there. Although I reported before that the Slave wasn't sending an ACK, I think I was wrong. When I poll the ACKSTAT in the Master, it comes back with a "0" which I thought was NO ACK, but in fact a 0 is reporting a good ACK.

I've also switched to 18F4685 on both Master and Slave just eliminate the possiblilty of bad chips. Same results.

I took Daniel's suggestion to try to read from the Slave instead of sending to it. The slave responds by loading the first digit in its SSPBUF but I'm not seeing it show up at the Master.

I notice that the Slave's D_A (SSPSTAT.5 ' SSP Data not Address) is always showing "1" for DATA and never have I seen a "0" for ADDRESS. Is that OK? How would that bit get changed?

Rswain

[DanPBP]

I'll try to buy a 18F2620 this week and run a few test Hope I can get it here, I live in Argentina, it's not always easy to find those "big brothers" ...

EDIT: I found a 18F452 laying around on the desk, will this serve the purpose???

[rswain]

Daniel - I'd be happy if any 18F would work. I'm starting to think something's wrong with PBP and 18F.

Thanks for your continued attempts to beat this problem into submission!

I'm going to switch to 16F877A (the old standby to see if I can get them to talk - once I get that, then we'll come back here and try again!

Robert