I2C Slave with a PIC

[DanPBP]

Hello Al,

Thank you very much for answering my message. You can't imagine how much I appreciate this working snipet for I2C slave communication.

I will test it right away and let you know how everything went.

Thanks a lot one more time!

Daniel.

[DanPBP]

Hello Al,

It works perfectly!!! I'm so happy now!!! Thank you very very much!!

I'll post my code as soon as it's done, so everybody else can use it.

Daniel.

[aratti]

Glad to hear that!

Al.

[DanPBP]

A short video:

The master on the left, a 16F877 is telling the first 16F88 (on the top) to turn on/off the LED, and then reads 24 from it. After that, the master tells the second 16F88 (on the bottom) to turn on/off the LED, and then reads 12 from it.

It's in slow motion because I was testing everything, but I discovered that the I2C protocol is very fast!

Al, thanks a lot one more time!

Daniel.

[rcbandwidth]

Hi Daniel: I would like to try out your code,could you post a link if not too much trouble.

Thanks RC

[DanPBP]

Sure! Let me know if you need anything else

Master 16f877 - External 4Mhz Crystal:

'-------------------------------------------------------------------------------
'-------------------------------------------------------------------------------
' Master
'-------------------------------------------------------------------------------
'-------------------------------------------------------------------------------

DEFINE OSC 4

'OPTION_REG.7 = 0

ADCON1 = 7

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

DEFINE I2C_SLOW 1

TRISB.5 = 1
TRISB.7 = 1

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

scl VAR PORTB.5		' i2c clock input
sda VAR PORTB.7     ' i2c data input

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

I2Caddress VAR BYTE

valor VAR BYTE

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

' Set LCD Data port
DEFINE LCD_DREG PORTD
' Set starting Data BIT (0 OR 4) IF 4-BIT bus
DEFINE LCD_DBIT 4
' Set LCD Register Select port
DEFINE LCD_RSREG PORTC
' Set LCD Register Select BIT
DEFINE LCD_RSBIT 6
' Set LCD Enable port
DEFINE LCD_EREG PORTC
' Set LCD Enable BIT
DEFINE LCD_EBIT 7
' Set LCD bus size (4 OR 8 bits)
DEFINE LCD_BITS 4
' Set number of lines ON LCD
DEFINE LCD_LINES 2
' Set command delay time in us
DEFINE LCD_COMMANDUS 2000
' Set Data delay time in us
DEFINE LCD_DATAUS 50

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

Pause 500       ' Wait for LCD to startup
LCDOut $fe, 1
LCDOut $fe, "Daniel"
Pause 500       ' Wait for LCD to startup

valor = 0

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

main:
      I2Caddress = $3

      LCDOut $fe, 1
      LCDOut "Writting 1 - LED ON..."
      Pause 500

      I2CWrite SDA, SCL, I2Caddress, [6], bogus ' Write offset to slave
      Pause 500

      LCDOut $fe, 1
      LCDOut "Writting 1 - LED OFF..."
      Pause 500

      I2CWrite SDA, SCL, I2Caddress, [8], bogus ' Write to slave
      Pause 500

      LCDOut $fe, 1
      LCDOut "Reading 1..."
      Pause 500

      I2CRead SDA, SCL, I2Caddress, [valor], bogus ' Read from slave
      LCDOut $fe, 1
      LCDOut "Value: ", DEC valor
      Pause 500

      '--------

      I2Caddress = $5

      LCDOut $fe, 1
      LCDOut "Writting 2 - LED ON..."
      Pause 500

      I2CWrite SDA, SCL, I2Caddress, [4], bogus ' Write to slave
      Pause 500

      LCDOut $fe, 1
      LCDOut "Writting 2 - LED OFF..."
      Pause 500

      I2CWrite SDA, SCL, I2Caddress, [10], bogus ' Write to slave
      Pause 500

      LCDOut $fe, 1
      LCDOut "Reading 2..."
      Pause 500

      I2CRead SDA, SCL, I2Caddress, [valor], bogus ' Read from slave
      LCDOut $fe, 1
      LCDOut "Value: ", DEC valor
      Pause 500

      '--------

      GoTo main       ' Do it forever

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

bogus:
		LCDOut $fe,1, "Time out"	' I2C command timed out
		Pause 500

		GoTo main

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

End

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

[DanPBP]

1' Slave - 16F88 - Internal 8Mhz

'------------------------------------------------------------------------------
'------------------------------------------------------------------------------
' Slave
'------------------------------------------------------------------------------
'------------------------------------------------------------------------------

@ device pic16f88, intrc_osc_noclkout	' system clock options
@ device pic16f88, wdt_on			' watchdog timer
@ device pic16f88, pwrt_on			' power-on timer
@ device pic16f88, mclr_off			' master clear options (internal)
@ device pic16f88, protect_off		' code protect off

'--- set device ---------------------------------------------------------------

DEFINE OSC 8
OSCCON = %01110001 '8mhz

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

CMCON = 7
ADCON1 = 0 ' Disable A/D converter
ADCON0 = 0
ANSEL = 0 ' all analog pins to digital

'--- tris port config here (don't use SCL & SDA pins other than I2C) ----------

DEFINE I2C_HOLD 1

TRISB.1 = 1
TRISB.4 = 1

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

SDADIR VAR TRISB.1
SCLDIR VAR TRISB.4

'--- Define here your variables and alias -------------------------------------

LEDT VAR PORTA.2
LEDL VAR PORTB.7
LEDM VAR PORTB.6
LEDR VAR PORTB.5
readcnt VAR BYTE
datain VAR BYTE
WrData VAR BYTE

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

SSPIF               VAR PIR1.3    ' SSP (I2C) interrupt flag
SSPIE               VAR PIE1.3 
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 SSPCON.4  ' SSP (I2C) SCK Release Control
SSPEN               VAR SSPCON.5  ' SSP (I2C) Enable
SSPOV               VAR SSPCON.6  ' SSP (I2C) Receive Overflow Indicator
WCOL                VAR SSPCON.7  ' SSP (I2C) Write Collision Detect
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 defintion ------------------------------------------------------

RxBufferLEN         CON 1       
RxBuffer            VAR BYTE[Rxbufferlen]
RxBufferIndex       VAR BYTE

'--- Tx Buffer defintion ------------------------------------------------------

TxBufferLEN         CON 1
TxBuffer            VAR BYTE[txbufferlen]
TxBufferIndex       VAR BYTE

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

I2Caddress          CON $3 ' Make address = 3

'--- Initialize I2C slave mode ------------------------------------------------

SCLDIR = 1          ' SCL must be an input before enabling interrupts
SDADIR = 1   
SSPADD = I2Caddress ' Set our address
SSPCON = $36        ' Set to I2C slave with 7-bit address
SSPSTAT = 0
SSPIE = 1 
SSPIF = 0 
RxBufferIndex = 0
TxBufferIndex = 0

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

GoTo main

'--- I2C subroutine  ----------------------------------------------------------

i2cslave:                                      ' I2C slave subroutine
          SSPIF = 0                            ' Clear interrupt flag
          IF R_W = 1 Then i2crd                ' Read data from us
          IF BF = 0 Then i2cexit               ' Nothing in buffer so exit
          IF D_A = 1 Then i2cwr                ' Data for us (not address)
          IF SSPBUF != I2Caddress Then i2cexit ' Clear the address from the buffer
          readcnt = 0                          ' Mark as first read
          GoTo i2cexit

i2cwr:                                ' 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 i2cexit

i2crd:                                      ' I2C read data from us
       IF D_A = 0 Then
          TxBufferIndex = 0
       EndIF

       While STAT_BF : Wend                        ' loop 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
             
i2cexit:
         Return

'--- End I2C subroutine  ------------------------------------------------------

Main:
      txbuffer = 12

      IF SSPIF = 1 Then
         GoSub i2cslave
      EndIF

      SSPOV = 0
      WCOL = 0

      Select Case RxBuffer[0]
             Case 6
                     High LEDT
             Case 8
                     Low LEDT
      End Select

      WrData=0  
      GoTo Main


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

End

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