/***********************************************************
	Chris Foster and Jeff Puchalski
	ECE 476 Spring 2003
	Project - 84256A 32K SRAM Chip Test
***********************************************************/

#include <Mega32.h>
#include <delay.h>

#define RESET 0
#define WRITE 1
#define READ  2
#define DONE  3

unsigned char state;

void main(void) {
	unsigned char c;

	DDRA=0xff;		// PORT A is memory address lines A0-A7
	PORTA=0x00;
	DDRB=0xff;		// PORT B is memory address lines A8-A12,CE,OE,WE
					// note that you only have room for 13 address lines
					// using two ports, which limits you to 8K of memory
					// CE := chip enable (but doesn't seem to do anything?)
					// OE := output enable (a.k.a. read)
					// WE := write enable
	PORTB=0b11100000;
	DDRC=0xff;		// PORT C is the LEDs
	DDRD=0xff;		// PORT D is the data bus likes D0-D7

	state = RESET;
	c = 0;

	while (1) {
		switch (state) {
			case RESET :
				state = WRITE;
				PORTC=0x00;			// turn on all the LEDs
				delay_ms(1000);
				break;
			case WRITE :
				PORTA=0b00101010;	// set the address..
				PORTB=0b11100000;	// ..and make sure r/w are disabled

				PORTB=0b01100000;	// flip WE low (on)
				PORTD=0b01001110;	// write the data
				PORTB=0b11100000;	// flip WE high (off)

				state = READ;
				PORTC = 0xff;		// turn off all the LEDs
				delay_ms(2000);
				break;
			case READ :
				DDRD=0x00;
				PORTA=0b00101010;	// set the address..
				PORTB=0b11100000;	// ..and make sure r/w are disabled

				PORTB=0b10100000;	// flip OE low (on)
				c=PIND;				// read the data
				PORTB=0b11100000;	// flip OE high (off)

				PORTC=~c;			// display the data read back to the LEDs
				state = DONE;
				break;
			case DONE :
				while (1);			// stay here forever!! (or till reset)
				break;
		}
   	}
}