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I2C Slave problems with a PIC18F6622

 
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SB



Joined: 15 Jan 2004
Posts: 10

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I2C Slave problems with a PIC18F6622
PostPosted: Tue Jan 22, 2008 11:37 am     Reply with quote
I am using the Ex_slave.c example on a Pic18F6622 with a Diolan USB to I2C interface adapter.
I am unable to read from the Pic, the Diolan times out and reports that the Slave has dropped the SDA and SCL lines.

I have tried using the second I2C on the pic with the same results.
I can program some DAC's which I have on the second I2c via the Diolan adapter so I am pretty sure that my hardware is ok.

I have tried the same code with a Pic16F88 and the Diolan adapter and it works without any problems.

Has anyone used the 18F6622 as an I2C slave?
(I am using PCWH V3.234)

Code:

#include <18F6622.h>
#device adc=10

#FUSES NOWDT   
#FUSES WDT128   
#FUSES INTRC_IO       
#FUSES NOPROTECT     
#FUSES IESO         
#FUSES BROWNOUT   
#FUSES BORV25             
#FUSES NOPUT         
#FUSES NOCPD         
#FUSES STVREN         
#FUSES NODEBUG 
#FUSES NOLVP         
#FUSES NOWRT   
#FUSES NOCPB     
#FUSES NOEBTRB   
#FUSES NOEBTR     
#FUSES NOWRTD       
#FUSES NOWRTC   
#FUSES NOWRTB   
#FUSES FCMEN     
#FUSES LPT1OSC     
#FUSES NOMCLR 
#FUSES NOXINST
#FUSES BBSIZ1K

#use delay(clock=8000000)
#use     i2c(Slave,sda=PIN_C4,scl=PIN_C3,address=0xa0,force_hw)

BYTE address;
BYTE buffer[0x10] = {1,2,3,4,5,6,7,8,9,0};

#INT_SSP
void ssp_interupt ()
{
   int8 incoming;
   int8 state;

   state = i2c_isr_state();
   if(state < 0x80)                     //Master is sending data
   {
      incoming = i2c_read();
      if(state == 1)                     //First received byte is address
      {
         address = incoming;
      }
      if(state == 2)                     //Second received byte is data
      {
         buffer[address] = incoming;
     }
   }
   if(state == 0x80)                     //Master is requesting data
   {
     i2c_write(buffer[address]);
   }
}

void main()
{
   setup_adc_ports(AN0_TO_AN1|VSS_VDD);
   setup_adc(ADC_CLOCK_INTERNAL);

   setup_timer_0(RTCC_INTERNAL|RTCC_DIV_8);
   setup_wdt(WDT_OFF);
   setup_timer_1(T1_DISABLED);
   set_timer1(64535);   
   setup_timer_2(T2_DISABLED,0,1);
   setup_comparator(NC_NC_NC_NC);
   setup_vref(FALSE);
   enable_interrupts(GLOBAL);
   enable_interrupts(INT_SSP);

   while(TRUE)
   {
     restart_wdt();
   }
}
SB



Joined: 15 Jan 2004
Posts: 10

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PostPosted: Thu Jan 24, 2008 8:54 am     Reply with quote
Just in case anyone is interested but I managed to fix my problem.

The i2c_isr_state() routine checks bit 0 of the SSP1BUF to see if it is a read or a write.
For some reason in the chip you have to look at bit 2 of SSP1STAT to see if it is a read or write.

If anyone know why this is the case I would be interested to know.

So using someones code from this forum I modified it slightly to look at the SSP1STAT.2 instead of SSP1BUF.0

Code:

#byte SSP1STAT = 0xFC7
#bit DA_BIT = SSP1STAT.5
#bit RW_BIT = SSP1STAT.2

#inline
int8 my_i2c_isr_state(void)
{
   static int8 i2c_state = 0x03;   
   int8 retval;
   
   if(!DA_BIT)          // If address byte was received
   {
      i2c_state = 0;    // Then clear state.
      if(RW_BIT)        // If it is a Read address
      {
         bit_set(i2c_state, 7);  // Then set bit 7 of state.
      }
   }       
   retval = i2c_state;
   i2c_state++;       
   return(retval); 
}

#INT_SSP
void ssp_interupt ()
{
   int8 incoming;
   int8 state;
   state = my_i2c_isr_state();
   if(state < 0x80)                     //Master is sending data
   {
      incoming = i2c_read();
      if(state == 1)                     //First received byte is address
      {
         address = incoming;
     }
     if(state == 2)                     //Second received byte is data
     {
         buffer[address] = incoming;
     }
   }
   if(state == 0x80)                     //Master is requesting data
   {
     i2c_write(buffer[address]);
   }
}
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