/* A demonstration of LCD operation in 8 and 4-bit modes. controller is P89C668HBA, compiler is SDCC */

#define BIT8 //for 8-bit mode. Comment this line for 4-bit mode 

#define EN P2_7
#define RS P2_6
#define BL P2_5
#define CMD 0
#define DTA 1
#define CLEAR 	0
#define SET	1
#define ON 	0
#define OFF	1
#define GREEN_LED	P1_4
#define RED_LED		P1_0

__sbit __at (0x90) P1_0;
__sbit __at (0x94) P1_4;

__sbit __at (0x8C) TR0;
__sbit __at (0x8D) TF0;
__sbit __at (0xA5) P2_5;
__sbit __at (0xA6) P2_6;
__sbit __at (0xA7) P2_7;                                          

__sfr __at (0x8B) TH0;
__sfr __at (0x8A) TL0;
__sfr __at (0x89) TMOD;


/* #define BIT8 /\* a default choice of 8-bit LCD operation; Comment this */
/* 	      * line for 4-bit application.*\/ */


void delay_millisec(unsigned int delay)
{
	/* A subroutine for generating 1ms delay */
		
	TMOD |= 0x01; /* timer 0; mode 1 */
	TH0 = 0xF4;
	TL0 = 0x03; /* with 18.423MHz crystal; delay = 0.326*3068
		     * us--approximatly 1ms */
	
	for (  ; delay != 0; delay-- ) {

		TR0 = SET; /* start timer */

		while(TF0 == CLEAR)
			; /* wait for timer overflow */
		TF0 = CLEAR; /* clear flags */
	}
	TR0 = CLEAR; /* stop timer */
}


#ifdef BIT8 /* 8-bit mode specific functions */

#define DATA P0
__sfr __at (0x80) P0;


void write_to_lcd( bit rs, unsigned char byte)
{
	/* A function to write to LCD in 8-bit mode */
	
	RS = rs; /* select the register:- CMD command and DTA data */
	EN = SET;
	DATA = byte; /* put data on data bus */
	EN = CLEAR; /* A 1 to 0 transition on EN validates data on
		     * data line */
	delay_millisec(2);  /* ramdom wait till data is processed by
			     * LCD */
}



void init_lcd()
{
	/* 8-bit intialization process as defined in the OLIMEX
	 * datasheets */
	delay_millisec(20); /* delay greater than 15ms */	
	write_to_lcd( CMD, 0x30); /* function set command */
	delay_millisec(5); /* delay greater than 4.1 ms */
	write_to_lcd( CMD, 0x30); /* function set command */
	delay_millisec(1); /* delay greater than 100us */
	write_to_lcd( CMD, 0x30); /* function set command */

	/* LCD is initialized here */
	
	write_to_lcd( CMD, 0x3C); /* function set command:- 1/16 duty
				   * 5x10 dots */
	write_to_lcd( CMD, 0x08); /* display off */
	write_to_lcd( CMD, 0x01); /* clear display */
	write_to_lcd( CMD, 0x06); /* entry mode:- display ON,shift
				   * OFF */
	write_to_lcd( CMD, 0x0F); /* display ON, cursor ON, blink
				   * ON */
}

#endif


#ifndef BIT8 /* 4-bit mode specific functions */
#undef BIT8

/* upper nibble of LCD data line */
#define D7 P0_7
#define D6 P0_6
#define D5 P0_5
#define D4 P0_4

__sbit __at (0x87) P0_7;
__sbit __at (0x86) P0_6;
__sbit __at (0x85) P0_5;
__sbit __at (0x84) P0_4;


void write_4bit_to_lcd( bit rs, unsigned char byte)
{
	/* A function to write to LCD in 4-bit mode */
	
	RS = rs; /* select the register:- CMD command and DTA data */
	EN = SET;
	/* put the nibble on the data bus */
	D7 = (byte & 0x80) ? SET: CLEAR;
	D6 = (byte & 0x40) ? SET: CLEAR;
	D5 = (byte & 0x20) ? SET: CLEAR;
	D4 = (byte & 0x10) ? SET: CLEAR;
	
	EN = CLEAR; /* A 1 to 0 transition on EN validates data on
		     * data line */
	delay_millisec(5); /* ramdom wait till data is processed by
			    * LCD */
}


void write_to_lcd(bit rs, unsigned char byte)
{
	/* A function to write 8-bit data on 4-bit LCD */
	
	write_4bit_to_lcd(rs, (byte & 0xF0) ); /* write the upper
						* nibble first */
	write_4bit_to_lcd(rs, (byte << 4) ); /* write the lower
					      * nibble */
}



void init_lcd()
{
	/* 4-bit intialization process as defined in the OLIMEX
	 * datasheets */
	delay_millisec(20); /* delay greater than 15ms */	
	write_4bit_to_lcd( CMD, 0x30); /* function set command */
	delay_millisec(5); /* delay greater than 4.1 ms */
	write_4bit_to_lcd( CMD, 0x30); /* function set command */
	delay_millisec(1); /* delay greater than 100us */
	write_4bit_to_lcd( CMD, 0x30); /* function set command */

	/* module is initialized */
	
	write_4bit_to_lcd( CMD, 0x20); /* function sets interface to
					* 4-bit */
		
	write_to_lcd( CMD, 0x28); /* function set command:- 1/16
				   * duty 5x10 dots */
	write_to_lcd( CMD, 0x08); /* display off */
	write_to_lcd( CMD, 0x01); /* clear display */
	write_to_lcd( CMD, 0x06); /* entry mode:- display
				   * ON,shift OFF */
	write_to_lcd( CMD, 0x0F); /* display ON, cursor ON, blink
				   * ON */
}

#endif



void print_on_lcd( char *str )
{
	/* A function to display a string on LCD */
	unsigned char ch = 0;

	write_to_lcd( CMD, 0x01); /* clear display */
	write_to_lcd( CMD, 0x02); /* return home */
	write_to_lcd( CMD, 0x80 ); /* place cursor at first row, first
				    * column */
	while ( (str[ch] != 0) && (ch < 32)  ) { /* LCD can display a
						  * maximum of 32
						  * characters */
		if (ch == 16)
			write_to_lcd( CMD, 0xC0); /* move the cursor
						   * to line 2 */
		write_to_lcd( DTA, str[ch] );
		ch++;
	}
}


main()
{
	
	init_lcd(); 
	
#ifdef BIT8
	print_on_lcd("testing LCD 8 bit mode");
#endif

#ifndef BIT8
	print_on_lcd("LCD 4-bit mode test successful!!!!");
#endif	

	while(1) {
		BL ^= 1; /* toggle LCD backlight */
		RED_LED ^= 1;
		GREEN_LED ^= 1; 
		delay_millisec(60);
	}
}