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i2c_isr_state for array > 128 possible??

 
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kopin



Joined: 18 Dec 2008
Posts: 3

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i2c_isr_state for array > 128 possible??
PostPosted: Mon Mar 23, 2009 11:42 am     Reply with quote
I am trying to set up a PIC as a slave and be able to do indexed reads for 256 addresses at one time. I seem to have run into a limit of this function....

For example, the first read I do, the state is 0x80. The next read is 0x81. That would correspond to addresses 0x00 and 0x01. This works okay for reads up to 0x7F. However, it breaks after that.

Does anyone have some suggestions or possible work-arounds?

Thanks!

From the "returns" of i2c_isr_state():

Code:

state is an 8 bit int

0 - Address match received with R/W bit clear

1-0x7F - Master has written data; i2c_read() will immediately return the data

0x80 - Address match received with R/W bit set; respond with i2c_write()

0x81-0xFF - Transmission completed and acknowledged; respond with i2c_write()
PCM programmer



Joined: 06 Sep 2003
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PostPosted: Mon Mar 23, 2009 11:46 am     Reply with quote
If you want to make your own, expanded, version of i2c_isr_state(),
this information will help:

Commented .LST file for the i2c_isr_state() function:
http://www.ccsinfo.com/forum/viewtopic.php?t=28531&start=10

C source code for i2c_isr_state():
http://www.ccsinfo.com/forum/viewtopic.php?t=26477&start=3
kopin



Joined: 18 Dec 2008
Posts: 3

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PostPosted: Fri Mar 27, 2009 12:20 pm     Reply with quote
Thanks for the links, it really helped. I was able to get this working well.

I added a global variable (called i2cs_rw in the code below) to signify a read or write and saved the whole state (to i2c_state) instead of using one of those bits to signify a read or write.

Code:
#inline               //instantiates a copy every place it
long my_i2c_isr_state(void)      // is called
{
  static long i2c_state = 0x03;      //state variable
  long retval;            //variable to return

  if(!DA_BIT) {            //if slave address byte was received
    i2c_state = 0;           // then clear state.
    i2cs_rw = 0;            //default to write operation
    if(RW_BIT) i2cs_rw = 1;      // if it is a read oepration, set flag
  }
  retval = i2c_state;         //return the current state
  i2c_state++;            //auto-increment
  return(retval);          // but return current, not auto-inc
}


You would also have to change the standard interrupt service routine code as well to look for this read/write instead of state > 0x80.

Hope this helps someone else.
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