Codevision AVR 使用 TWI 访问外部 eeprom 24c02B

Question

我是 C 的初学者。我正在尝试写入和读取外部 eeprom (AT24c02B)，然后将存储在 eeprom 中的数据字节显示到 PORTB 中的 LED 或 LCD。所以我知道数据成功存储在eeprom中。

PORTB 中的 LED 低电平有效。

这是代码，我是从 cvAVR 帮助中得到的：

#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，调用什么变量才能显示8个LED的字节数？

ex: after writing bytes: 0xF0, then LED in PORTB will be 0xF0 (11110000)

我在网上搜索过，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);

有人可以解释一下吗？ &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

如有任何答复和评论，我们将不胜感激。
谢谢，请原谅我的英语。

一平

Answer 1

TWI 是一种从主设备向从设备双向传输数据的方法。在您的情况下，您的代码在主机上运行，而 EEPROM 是从机。数据同时在设备之间移动。也就是说，一个字节被传输到从机同时一个字节被从从机传回。

twi.h中给出的函数描述了启动这个过程的方法，参数在那里描述。

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从中获取数据的缓冲区的地址和要获取的长度。

后面两个是接收数据的缓冲区地址和长度

要将0x55写入特定地址的EEPROM，需要向EEPROM发送三个字节。这些为您安排在一个结构中。如果你给函数结构的地址和长度 3，函数会为你处理。 (unsigned char *) &twi_eeprom 是结构的地址。

您现在不关心接收，所以只需将 0 和 0 作为要接收的地址和长度。

读回值时，只需要将字节的地址发送到EEPROM即可。所以发送相同的结构，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。

Codevision AVR 使用 TWI 访问外部 eeprom 24c02B

Codevision AVR access external eeprom 24c02B using TWI

c

embedded

microcontroller

avr

eeprom