///////////////////////////////////////////////////////////////////////////
////   Library for a MicroChip 93C56 configured for a x8 org           ////
////                                                                   ////
////   init_ext_eeprom();    Call before the other functions are used  ////
////                                                                   ////
////   write_ext_eeprom(a, d);  Write the byte d to the address a      ////
////                                                                   ////
////   d = read_ext_eeprom(a);   Read the byte d from the address a    ////
////                                                                   ////
////   The main program may define eeprom_select, eeprom_di, eeprom_do ////
////   and eeprom_clk to override the defaults below.                  ////
////                                                                   ////
///////////////////////////////////////////////////////////////////////////
////        (C) Copyright 1996,1997 Custom Computer Services            ////
//// This source code may only be used by licensed users of the CCS C   ////
//// compiler.  This source code may only be distributed to other       ////
//// licensed users of the CCS C compiler.  No other use, reproduction  ////
//// or distribution is permitted without written permission.           ////
//// Derivative programs created using this software in object code     ////
//// form are not restricted in any way.                                ////
////////////////////////////////////////////////////////////////////////////

#ifndef EEPROM_SELECT

#define EEPROM_SELECT PIN_B7
#define EEPROM_CLK    PIN_B6
#define EEPROM_DI     PIN_B5
#define EEPROM_DO     PIN_B4

#endif

#define EEPROM_ADDRESS byte
#define EEPROM_SIZE    256

void init_ext_eeprom() {
   byte cmd[2];
   byte i;

   output_low(EEPROM_DI);
   output_low(EEPROM_CLK);
   output_low(EEPROM_SELECT);

   cmd[0]=0x80;
   cmd[1]=0x9;

   for(i=1;i<=4;++i)
      shift_left(cmd,2,0);
   output_high(EEPROM_SELECT);
   for(i=1;i<=12;++i) {
      output_bit(EEPROM_DI, shift_left(cmd,2,0));
      output_high(EEPROM_CLK);
      output_low(EEPROM_CLK);
   }
   output_low(EEPROM_DI);
   output_low(EEPROM_SELECT);
}


void write_ext_eeprom(EEPROM_ADDRESS address, byte data) {
   byte cmd[3];
   byte i;

   cmd[0]=data;
   cmd[1]=address;
   cmd[2]=0xa;

   for(i=1;i<=4;++i)
      shift_left(cmd,3,0);
   output_high(EEPROM_SELECT);
   for(i=1;i<=20;++i) {
      output_bit(EEPROM_DI, shift_left(cmd,3,0));
      output_high(EEPROM_CLK);
      output_low(EEPROM_CLK);
   }
   output_low(EEPROM_DI);
   output_low(EEPROM_SELECT);
   delay_ms(11);
}


byte read_ext_eeprom(EEPROM_ADDRESS address) {
   byte cmd[3];
   byte i,data;

   cmd[0]=0;
   cmd[1]=address;
   cmd[2]=0xc;

   for(i=1;i<=4;++i)
      shift_left(cmd,3,0);
   output_high(EEPROM_SELECT);
   for(i=1;i<=20;++i) {
      output_bit(EEPROM_DI, shift_left(cmd,3,0));
      output_high(EEPROM_CLK);
      output_low(EEPROM_CLK);
      if(i>12)
        shift_left(&data,1,input(EEPROM_DO));
   }
   output_low(EEPROM_SELECT);
   return(data);
}