1.介绍

I2C总线是Philips半导体公司（现在的NXP半导体公司）开发的一种简单、双向二线制同步串行总线。它只需要两根线即可在连接于总线上的器件之间传送信息。SDA（串行数据线）和SCL（串行时钟线）都是双向I/O线，接口电路为开漏输出．需通过上拉电阻接电源VCC．当总线空闲时．两根线都是高电平。

在I2C器件开始通信（传输数据）之前，串行时钟线SCL和串行数据线SDA线由于上拉的原因处于高电平状态，此时I2C总线处于空闲状态。如果主机（此处指FPGA）想开始传输数据，只需在SCL为高电平时将SDA线拉低，产生一个起始信号，从机检测到起始信号后，准备接收数据，当数据传输完成，主机只需产生一个停止信号，告诉从机数据传输结束，停止信号的产生是在SCL为高电平时， SDA从低电平跳变到高电平，从机检测到停止信号后，停止接收数据。

在串行时钟线SCL为低电平状态时， SDA允许改变传输的数据位（ 1为高电平， 0为低电平），在SCL为高电平状态时， SDA要求保持稳定，相当于一个时钟周期传输1bit数据，经过8个时钟周期后，传输了8bit数据，即一个字节。第8个时钟周期末，主机释
放SDA以使从机应答，在第9个时钟周期，从机将SDA拉低以应答；如果第9个时钟周期， SCL为高电平时， SDA未被检测到为低电平，视为非应答，表明此次数据传输失败。第9个时钟周期末，从机释放SDA以使主机继续传输数据，如果主机发送停止信号，此次传输结束。数据以8bit即一个字节为单位串行发出，其最先发送的是字节的最高位。

eeprom选用at24c02，at24c64

器件地址

写数据

读数据

2.硬件

FPGA管脚配置

信号名	方向	管教	端口说明
sys_clk	input	E1	系统时钟50M
sys_rst_n	input	M1	系统复位，低电平有效
led0	output	F3
led1	output	F5
key0	input	G5
key1	input	L7
key2	input	J6
i2c_scl	output	D5	I2C时钟
i2c_sdk	input	C3	I2C数据

3.程序设计

always @(posedge i2c_clk or negedge rst) beginif(!rst)beginstate 	   <= s0_idle_start;r_rd_sel   <= SDA_WRITE;sda_buffer <= 1'd1;buffer	   <= 8'd0;bit_cnt    <= 4'd0;rd_data	   <= 8'd0;I2C_WorR   <= I2C_READ;endelse begincase(state)s0_idle_start:beginif	   ((key_flag == 1'd1) && (key_value == 3'b110))begin	// readr_rd_sel   <= SDA_WRITE;		// system control the iic sda writesda_buffer <= 1'd0;				// start signalstate      <= s1_device_addr;	// state changebuffer	   <= 8'b1010_0000;I2C_WorR   <= I2C_READ;rd_data    <= 8'd0;endelse if((key_flag == 1'd1) && (key_value == 3'b101))begin	// writer_rd_sel   <= SDA_WRITE;		// system control the iic sda writesda_buffer <= 1'd0;				// start signalstate      <= s1_device_addr;	// state changebuffer	   <= 8'b1010_0000;I2C_WorR   <= I2C_WRITE;endelse beginstate <= s0_idle_start;endends1_device_addr 	 	 :beginif(!scl)begin	// if scl is low levelif(bit_cnt < 4'd8)beginr_rd_sel   <= SDA_WRITE;sda_buffer <= buffer[7];buffer     <= {buffer[6:0],buffer[7]};bit_cnt    <= bit_cnt + 1'b1;endelse beginstate    <= s2_device_addr_ack;bit_cnt  <= 4'd0;r_rd_sel <= SDA_READ;		// sda receive dataendendends2_device_addr_ack 	 :beginif(scl)begin		// if scl is high levelr_rd_sel <= SDA_WRITE;if(sda == 1'd0)beginif(DATA_ADDR_WIDTH)begin	// 16bit data state  <= s3_word_addr_high;buffer <= 8'h00;endelse beginstate <= s5_word_addr_low;buffer <= 8'h01;endendelse begin//state <= s5_word_addr_low;state <= s0_idle_start;endendends3_word_addr_high	 :beginif(!scl)begin	// if scl is low levelif(bit_cnt < 4'd8)beginsda_buffer <= buffer[7];buffer     <= {buffer[6:0],buffer[7]};bit_cnt	   <= bit_cnt + 1'd1;endelse beginstate	 <= s4_word_addr_high_ack;bit_cnt  <= 4'd0;r_rd_sel <= SDA_READ;	// sda receive dataendendends4_word_addr_high_ack:beginif(scl)beginr_rd_sel <= SDA_WRITE;if(sda == 1'd0)beginstate  <= s5_word_addr_low;buffer <= 8'h01;endelse beginstate <= s0_idle_start;//state  <= s5_word_addr_low;endendends5_word_addr_low	 :beginif(!scl)begin	// if scl is low levelif(bit_cnt < 4'd8)beginsda_buffer <= buffer[7];buffer     <= {buffer[6:0],buffer[7]};bit_cnt	   <= bit_cnt + 1'd1;endelse beginstate	 <= s6_word_addr_low_ack;bit_cnt  <= 4'd0;sda_buffer <= 1'd1;r_rd_sel <= SDA_READ;	// sda receive dataendendends6_word_addr_low_ack :beginif(scl)beginr_rd_sel   <= SDA_WRITE;if(sda == 1'd0)beginbuffer <= 8'h53;	// character "S"if(I2C_WorR == I2C_WRITE)begin	// write iicstate <= s7_data_write;sda_buffer <= 1'd0;		// put down sda in order to prevent the generation of stop signalendelse begin				// iic readstate <= s9_read_start;sda_buffer <= 1'd1;		// put down sda in order to generate a start signalendendelse beginstate <= s0_idle_start;
//						if(rw_en == 2'b01)begin
//							state <= s7_data_write;
//						end
//						else begin
//							state <= s9_read_start;
//						endendendends7_data_write		 :beginif(!scl)begin // scl low levelif(bit_cnt < 4'd8)beginbit_cnt 	<= bit_cnt +1'd1;sda_buffer	<= buffer[7];buffer  	<= {buffer[6:0],buffer[7]};endelse beginstate	 <= s8_data_write_ack;bit_cnt  <= 4'd0;r_rd_sel <= SDA_READ;sda_buffer <= 1'd0;endendends8_data_write_ack	 :beginif(scl)beginr_rd_sel   <= SDA_WRITE;sda_buffer <= 1'd0;if(sda == 1'd0)beginstate <= s13_stop;endelse begin
//						state <= s13_stop;state <= s0_idle_start;endendends9_read_start		 :beginif(scl)begin	// scl high levelsda_buffer <= 1'd0;state	   <= s10_read_device_addr;buffer	   <= 8'b1010_0001;endends10_read_device_addr :beginif(!scl)begin	// if scl is low levelif(bit_cnt < 4'd8)beginr_rd_sel   <= SDA_WRITE;sda_buffer <= buffer[7];buffer     <= {buffer[6:0],buffer[7]};bit_cnt    <= bit_cnt + 1'b1;endelse beginstate    <= s11_read_decice_ack;bit_cnt  <= 4'd0;r_rd_sel <= SDA_READ;		// sda receive dataendendends11_read_decice_ack	 :beginif(scl)beginr_rd_sel   <= SDA_READ;if(sda == 1'd0)beginstate <= s12_data_read;endelse begin
//						state <= s12_data_read;state <= s0_idle_start;endendends12_data_read		 :beginif(scl)beginif(bit_cnt < 4'd8)beginbit_cnt <= bit_cnt + 1'd1;rd_data[7-bit_cnt] <= sda;endelse beginbit_cnt  <= 4'd0;state 	 <= s13_stop;r_rd_sel <= SDA_WRITE;sda_buffer <= 1'd0;endendends13_stop			 :beginif(scl)beginstate	   <= s0_idle_start;sda_buffer <= 1'd1;endenddefault:;endcaseend
end	

用sigaltap观察波形