writepage.c

一个AVR单片机at17c85的系统程序

// WritePage.c
// Writes PAGE_SIZE bytes at address from bufptr
// Starts writing at address 0 within the page
// Please refer to the application note titled: 
// "Programming Specification for Atmel's Configuration Memory E睵ROMS AT17C65/128/256/512/010" 
// found at www.atmel.com for detailed device address decoding and page address formatting
// After programming the data polling method is used to determine the end of 
// the internal programming cycle.
// Timer/Counter1 is used to ensure the polling code exits its while loop.

#include "at17c.h"

extern volatile unsigned char t1_timed_out;
 
extern unsigned char SendByte(unsigned char byte, unsigned char order);
extern void SendStartBit(void);
extern void SendStopBit(void);
extern void BitDelay(void);
 
void WritePage(unsigned int address, unsigned char *bufptr) {

unsigned char i;
unsigned char addr1;
unsigned char addr2;
unsigned char addr3;
unsigned char test_ack = 0xff;

    PORTB &= 0xfb; // bring SER_EN low
    BitDelay();
                
    addr1 = (unsigned char)(address >> 9);
    addr2 = (unsigned char)(address >> 1);
    addr3 = (unsigned char)(address << 7);
        
    SendStartBit();
    SendByte(AT17C010 + WRITE,MSB_FIRST);  // send device address byte with write bit
    SendByte(addr1,MSB_FIRST);                 // 1st address byte
    SendByte(addr2,MSB_FIRST);                 // 2nd address byte
    SendByte(addr3,MSB_FIRST);                 // 3rd address byte
 
    for (i = 0; i < PAGE_SIZE; i++)
        SendByte(bufptr[i],LSB_FIRST);
            
    SendStopBit();
              
    t1_timed_out = FALSE; // set in timer counter 0 overflow interrupt routine
 
    // 20 milli-second timeout
    // 7.3728MHz / 1024 = 7200 Hz
    // 7200 Hz = 138.8 us
    // 20 ms / 138.8 us = 144
    // 65536 - 144 = 65392 = ff70
    // interrupt on ffff to 0000 transition
    TCNT1H = 0xff;  
    TCNT1L = 0x70; // load counter
    TCCR1B = 0x05; // timer/counter 1 clock / 1024

    // continue sending start bit and device address until we get an ack back
    // data poll to program complete ... time out for error
    while (test_ack && !t1_timed_out) {
        SendStartBit();
        test_ack = SendByte(AT17C010 + WRITE,MSB_FIRST);  // send device address byte
    }
    TCCR1B = 0x00; // disable timer/counter 1 clock
    SendStopBit();

    PORTB |= 0x04; // bring SER_EN high
        
}