I2C lcd controller using PIC16F690

#include <16F690.h>

#device adc=8

#FUSES WDT                      //Watch Dog Timer
#FUSES HS                       //HS Oscilator
#FUSES NOPROTECT                //Code not protected from reading
#FUSES NOBROWNOUT               //No brownout reset
#FUSES NOMCLR                   //Master Clear pin used for I/O
#FUSES NOCPD                    //No EE protection
#FUSES NOPUT                    //No Power Up Timer
#FUSES NOIESO                   //Internal External Switch Over mode disabled
#FUSES NOFCMEN                  //Fail-safe clock monitor disabled

#use delay(clock=20000000)
#use i2c(Slave,Fast,sda=PIN_B7,scl=PIN_B6,restart_wdt,force_hw,address=0xAA)



//how big the buffer is .. ~78 is the largest I could make on 16f690
//33 is enough for lcd operations, everything else is pure bonus :)
#define ALCTD 75

BYTE incoming, state;
BYTE address;
BYTE buffer[ALCTD];
BYTE changed[ALCTD];

#int_SSP
void  SSP_isr(void) {
  state = i2c_isr_state();

  if(state == 1){  //First received byte is address
    incoming = i2c_read();
    address = incoming;
    if (address > ALCTD) address = 0;
  }

  if(state == 2){  //Second received byte is data
    incoming = i2c_read();
    buffer[address] = incoming;
    changed[address] = 1;
  }

  if(state == 0x80){  //Master is asking for data
    i2c_write (buffer[address]);
  }
}

// PIC     LCD
// C0      enable
// C1      rs
// C2      rw
// C3      NC
// C4      D4
// C5      D5
// C6      D6
// C7      D7

struct lcd_pin_map {                 // This structure is overlayed
           BOOLEAN enable;           // on to an I/O port to gain
           BOOLEAN rs;               // access to the LCD pins.
           BOOLEAN rw;               // The bits are allocated from
           BOOLEAN unused;           // low order up.  ENABLE will
           int     data : 4;         // be pin B0.
        } lcd;

#locate lcd = getenv("sfr:PORTC")    // This puts the entire structure over the port
#define set_tris_lcd(x) set_tris_c(x)

#define lcd_type 2           // 0=5x7, 1=5x10, 2=2 lines
#define lcd_line_two 0x40    // LCD RAM address for the second line

BYTE const LCD_INIT_STRING[4] = {0x20 | (lcd_type << 2), 0xc, 1, 6};

struct lcd_pin_map const LCD_WRITE = {0,0,0,0,0}; // For write mode all pins are out
struct lcd_pin_map const LCD_READ = {0,0,0,0,15}; // For read mode data pins are in

BYTE lcd_read_byte() {
      BYTE low,high;
      set_tris_lcd(LCD_READ);
      lcd.rw = 1;
      delay_cycles(1);
      lcd.enable = 1;
      delay_cycles(1);
      high = lcd.data;
      lcd.enable = 0;
      delay_cycles(1);
      lcd.enable = 1;
      delay_us(1);
      low = lcd.data;
      lcd.enable = 0;
      set_tris_lcd(LCD_WRITE);
      return( (high<<4) | low);
}

void lcd_send_nibble( BYTE n ) {
      lcd.data = n;
      delay_cycles(1);
      lcd.enable = 1;
      delay_us(2);
      lcd.enable = 0;
}

void lcd_send_byte( BYTE address, BYTE n ) {
      lcd.rs = 0;
      while ( bit_test(lcd_read_byte(),7) ) ;
      lcd.rs = address;
      delay_cycles(1);
      lcd.rw = 0;
      delay_cycles(1);
      lcd.enable = 0;
      lcd_send_nibble(n >> 4);
      lcd_send_nibble(n & 0xf);
}

void lcd_init() {
    BYTE i;
    set_tris_lcd(LCD_WRITE);
    lcd.rs = 0;
    lcd.rw = 0;
    lcd.enable = 0;
    delay_ms(15);
    for(i=1;i<=3;++i) {
       lcd_send_nibble(3);
       delay_ms(5);
    }
    lcd_send_nibble(2);
    for(i=0;i<=3;++i)
       lcd_send_byte(0,LCD_INIT_STRING[i]);
}

void main(){
   BYTE i;

   setup_adc_ports(NO_ANALOGS|VSS_VDD);
   setup_adc(ADC_OFF);
   setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1);
   setup_wdt(WDT_2304MS|WDT_DIV_16);
   setup_timer_1(T1_DISABLED);

   lcd_init();

   enable_interrupts(INT_SSP);
   enable_interrupts(GLOBAL);

   //init buffers
   for(i=0;i<32;i++){
     changed[i]=0;
     buffer[i]=0;
   }

  while (TRUE){
    #asm
    clrwdt
    #endasm

    //update 1st line
    for(i=0;i<16;i++){
      if (changed[i]){
        changed[i]=0;
        lcd_send_byte(0,0x80|i); //go to 1.row, i'th place
        lcd_send_byte(1,buffer[i]);        
      }
    }

    //update 2nd line
    for(i=16;i<32;i++){
      if (changed[i]){
        changed[i]=0;
        lcd_send_byte(0,0x80|(i+lcd_line_two-16)); //go to 2.row, i'th place
        lcd_send_byte(1,buffer[i]);        
      }
    }

    if (changed[32]){ // send controll code
      changed[32] = 0;
      lcd_send_byte(0,1); //clear screen    
    }

    for(i=33;i<ALCTD;i++){
     //do whatever .. controll the free oi pins on the uC...
    }

  }
}

void i2c_putc(unsigned char c){
  unsigned char static position = 0;
  if (c == '\f'){ // \f will clear screen
    I2C_Start();
    I2C_Wr(0xAA);
    I2C_Wr(32);
    I2C_Wr('x');
    I2C_Stop();
    position=0;
  } else if (c=='\n'){  //move position to beginning of the second line
    position=16;
  } else {
    I2C_Start();
    I2C_Wr(0xAA);
    I2C_Wr(position++);
    I2C_Wr(c);
    I2C_Stop();
    if (position > 31) position=0;
  }
}

void i2c_print(char *c){
   unsigned char i;
   i=0;
   while (c[i]){
      i2c_putc(c[i]);
      i++;
   }
}

char x[] = "\fHello World!\nsecond line";

void main(){
  Delay_ms(200); //wait for the i2c slaves to come online
  I2C_Init(100000); //"fast" i2c initialisation
  i2c_print(x);
}

#define SCL  PORTA.F0
#define SDA  PORTA.F1

#define SCLt TRISA.F0
#define SDAt TRISA.F1

#define ADDR 0xAA

unsigned char data;
unsigned char cnt;
unsigned char posX;
unsigned char posY;

void readByte(){
  cnt  = 0;
  data = 0;
  while(cnt < 8){
    while ( SCL);  //wait for SCL to go down
    while (!SCL);  //wait SCL to go high
    data = (data << 1) | SDA;
    cnt++;
  }
  __asm CLRWDT
}

void ack(){
  while(SCL);
  SDAt = 0;
  SDA = 0;
  while(!SCL); while(SCL);
  SDAt = 1;
}

void main(){
   SCLt = 1;
   SDAt = 1;
   CMCON = 0b00000111 ; //ALL Digital (comparators off)
   TRISB = 0;
   PORTB = 0;
   TRISA.F2 = 0;
   PORTA.F2 = 0;

   posX = 1;
   posY = 1;
   data = '-';

   Lcd_Custom_Config(&PORTB, 7, 6, 5, 4, &PORTB, 2, 1, 3);
   Lcd_Custom_Cmd(LCD_CLEAR);
   Lcd_Custom_Cmd(LCD_CURSOR_OFF);
   Lcd_Custom_Chr_Cp(data);

   __asm CLRWDT

   while(1){ //main loop
mainloop:
     SCLt = 1;
     SDAt = 1;
     while(! (SDA & SCL)) __asm CLRWDT;
     while (SDA) __asm CLRWDT ;
     if (SCL){ //START condition
         readByte(); // READ ADDRESS  (i2c id)

         //ACK if we are targeted   (ignore Read bit)
         if (data == ADDR ){
           ack();
         } else {
           goto mainloop;  // not for us, ignore it
         }

         readByte(); // Position
         ack();
         if (data < 16){
           posX = data+1;
           posY = 1;
         } else {
           posX = data-15;
           posY = 2;
         }

         readByte(); // READ DATA
         ack();
         SCLt = 0;     //Hold the clock line low
         SCL = 0;      //Untill you finish writing to LCD
         if (data == '\f') {
           Lcd_Custom_Cmd(LCD_CLEAR);
           posX = 1;
           posY = 1;
         } else if (data == '\n') {
           posY=2;
           posX=1;
         } else {
           Lcd_Custom_Chr(posY, posX, data);
           posX++;
         }
         SCLt = 1;
     } // if
   }// while
} // main