码视AVR访问外部eeprom 24c02B使用TWI

Question

我是c的初学者。我试图写入和读取外部eeprom (AT24c02B)，然后显示存储在eeprom到PORTB和或LCD中的LED的数据字节。所以我知道数据成功地存储在eeprom中。

PORTB LED低电平有效

这是代码，我从cvAVR帮助:

#include <mega16a.h>
// Alphanumeric LCD functions
#include <alcd.h>
// Declare your global variables here
// TWI functions
#include <twi.h>
#include <delay.h>
/* 7 bit TWI bus slave address of the AT24C02B 2kbyte EEPROM */
#define EEPROM_TWI_BUS_ADDRESS (0xA0 >> 1)
void main(void)
{
// Declare your local variables here
struct
     {
     struct
          {
          unsigned char msb;
          unsigned char lsb;
          } addr;
     unsigned char data;
     } twi_eeprom;

unsigned char eeprom_rd_data;
// Input/Output Ports initialization
// Port A initialization
// Function: Bit7=Out Bit6=Out Bit5=Out Bit4=Out Bit3=Out Bit2=Out Bit1=Out Bit0=Out 
DDRA=(1<<DDA7) | (1<<DDA6) | (1<<DDA5) | (1<<DDA4) | (1<<DDA3) | (1<<DDA2) | (1<<DDA1) | (1<<DDA0);
// State: Bit7=0 Bit6=0 Bit5=0 Bit4=0 Bit3=0 Bit2=0 Bit1=0 Bit0=0 
PORTA=(0<<PORTA7) | (0<<PORTA6) | (0<<PORTA5) | (0<<PORTA4) | (0<<PORTA3) | (0<<PORTA2) | (0<<PORTA1) | (0<<PORTA0);
// Port B initialization
// Function: Bit7=Out Bit6=Out Bit5=Out Bit4=Out Bit3=Out Bit2=Out Bit1=Out Bit0=Out 
DDRB=(1<<DDB7) | (1<<DDB6) | (1<<DDB5) | (1<<DDB4) | (1<<DDB3) | (1<<DDB2) | (1<<DDB1) | (1<<DDB0);
// State: Bit7=1 Bit6=1 Bit5=1 Bit4=1 Bit3=1 Bit2=1 Bit1=1 Bit0=1 
PORTB=(1<<PORTB7) | (1<<PORTB6) | (1<<PORTB5) | (1<<PORTB4) | (1<<PORTB3) | (1<<PORTB2) | (1<<PORTB1) | (1<<PORTB0);
// TWI initialization
// Mode: TWI Master
// Bit Rate: 100 kHz
twi_master_init(100);
// Alphanumeric LCD initialization
// Connections are specified in the
// Project|Configure|C Compiler|Libraries|Alphanumeric LCD menu:
// RS - PORTA Bit 0
// RD - PORTA Bit 1
// EN - PORTA Bit 2
// D4 - PORTA Bit 4
// D5 - PORTA Bit 5
// D6 - PORTA Bit 6
// D7 - PORTA Bit 7
// Characters/line: 16
lcd_init(16);
// Global enable interrupts
#asm("sei")
/* write the byte 0x55 to the AT24C02B EEPROM address 0x210 */
twi_eeprom.addr.msb=0x02;
twi_eeprom.addr.lsb=0x10;
twi_eeprom.data=0x55;
twi_master_trans(EEPROM_TWI_BUS_ADDRESS,(unsigned char *) &twi_eeprom,3,0,0);
/* 10ms delay to complete the write operation */
delay_ms(10);
/* read the byte back into the eeprom_rd_data variable */
twi_master_trans(EEPROM_TWI_BUS_ADDRESS,(unsigned char *) &twi_eeprom,2,&eeprom_rd_data,1);
while (1)
      {
      // Place your code here
      PORTB = ; //What variable should I call?
      delay_ms(3000);
      }
}  

twi.h

/******************************************************************************
 TWI driver library for the CodeVisionAVR C V2.05.1+ Compiler
 Copyright (C) 2010-2011 Pavel Haiduc, HP InfoTech S.R.L., All rights reserved.
*******************************************************************************/
#ifndef _TWI_INCLUDED_
#define _TWI_INCLUDED_
#include <stdbool.h>
// TWI transaction result values
#define TWI_RES_OK 0
#define TWI_RES_BUFFER_OVERFLOW 1
#define TWI_RES_ARBITRATION_LOST 2
#define TWI_RES_BUS_ERROR 3
#define TWI_RES_NACK_RECEIVED 4
#define TWI_RES_BUS_TIMEOUT 5
#define TWI_RES_FAIL 6
#define TWI_RES_UNKNOWN 7
extern unsigned char twi_tx_index; // data index in the transmit buffer
extern unsigned char twi_rx_index; // data index in the receive buffer
extern unsigned char twi_result; // holds the result of the last TWI transaction
// TWI master initialization
// bit_rate - SCL bit rate [kHz]
void twi_master_init(unsigned int bit_rate);
// function used for performing a TWI master transaction
// slave_addr - 7 bit address of the TWI slave with which the transaction must be performed
// tx_data - pointer to the buffer that holds the data to be transmitted to the slave
// tx_count - number of bytes that must be transmitted to the slave during the transaction
// rx_data - pointer to the buffer that holds the data received from the slave
// rx_count - number of bytes that must be received from the slave during the transaction
// returns true on success
bool twi_master_trans(
     unsigned char slave_addr,
     unsigned char *tx_data, unsigned char tx_count,
     unsigned char *rx_data, unsigned char rx_count);
// TWI slave initialization
// match_any_addr - if true, the slave match address logic responds to all received addresses
// addr - 7 bit address of the TWI slave
// rx_buffer - pointer to the slave receive buffer
// rx_buffer_size - size of the slave receive buffer
// tx_buffer - pointer to the slave transmit buffer
// slave_rx_handler - pointer to the TWI slave receive processing function
// slave_tx_handler - pointer to the TWI slave transmit processing function
void twi_slave_init(
     bool match_any_addr,
     unsigned char addr,
     unsigned char *rx_buffer,
     unsigned char rx_buffer_size,
     unsigned char *tx_buffer,
     bool (*slave_rx_handler)(bool rx_complete),
     unsigned char (*slave_tx_handler)(bool tx_complete)
     );
#pragma library twi.lib
#endif

我想问的是:
1. 写入eeprom后，我应该调用什么变量来显示8个LED上的字节?

ex:写入字节后:0xF0，那么PORTB中的LED将是0xF0 (11110000)

我确实在网上搜索过，但仍然对这行

感到困惑

twi_master_trans(EEPROM_TWI_BUS_ADDRESS,(unsigned char *) &twi_eeprom,3,0,0);

twi_master_trans(EEPROM_TWI_BUS_ADDRESS,(unsigned char *) &twi_eeprom,2,&eeprom_rd_data,1);

有人能解释一下吗?&twi_eeprom,3,0,0到底是什么意思?

设备:Atmega16a
程序:Codevision AVR 3.12
外部eeprom: AT24c02b

任何回答和评论都将是感激的。
谢谢，请原谅我的英语。

Ipin

Answer 1

TWI是一种从主设备向从设备双向传输数据的方法。在您的例子中，您的代码运行在主服务器上，而EEPROM是从服务器。数据在设备之间同时移动。也就是说，一个字节被传送到从机的同时，一个字节从从机被传送回来。

twi.h中给出的函数描述了启动此过程的方法，其中描述了参数。

unsigned char slave_addr,
unsigned char *tx_data, 
unsigned char tx_count,
unsigned char *rx_data, 
unsigned char rx_count

第一个参数是代码中给定的常量。

接下来的两个参数是要获取数据的缓冲区的地址和要获取的长度。

接下来的两个是用来存放接收到的数据的缓冲区的地址和长度。

要将0x55写入特定地址的EEPROM，需要向EEPROM发送3个字节。它们被安排在一个结构体中。如果你给函数结构体的地址和长度为3，函数会为你处理它。(unsigned char *) &twi_eeprom是结构体的地址。

您现在不关心接收，因此只需输入0和0作为接收的地址和长度。

当你读回值时，你只需要将字节的地址发送到EEPROM。所以发送相同的结构体，但只有两个字节。您还需要保存接收到的字节。它将进入变量eeprom_rd_data，因为您将该变量的地址传递给了函数。将PORRTB设置为等于eeprom_rd_data以显示其值