RS232串口通信实验Verilog

独孤求真 posted @ 2010年9月21日 20:24 in CPLD,FPGA学习 with tags RS232;串口;Verilog; , 17487 阅读

RS232串口通信实验几乎是入门必做实验，这是本人学习过程中做的练习。首先是分频模块，分频模块是学习了OpenCore上的uart2bus项目的。http://opencores.org/project,uart2bus
该模块接收任意频率的输入频率(clk_i)，输出频率(记为clk_o)由baud_freq_i和baud_limit_i根据以下公式计算，使用时首先需要根据输入频率和输出频率计算出baud_freq_i和baud_limit_i这两个参数。

[tex] baud\_freq = \frac{clk\_o}{GCD(clk\_i, clk\_o)}[/tex]

[tex] baud\_limit = \frac{clk\_i}{GCD(clk\_i, clk\_o)} - baud\_freq [/tex]

公式里的GCD(Greatest Common Divisor)表示取2个数的最大公约数。

这里系统时钟频率为50MHz，串口频率为9600，通常我们是在中间进行采样。因此分频模块分出来的频率为16*9600。模块如下：

/* 
 * this module has been changed to receive the baud rate 
 * dividing counter from registers.
 * the two registers should be calculated as follows:
 * first register:
 * 	baud_freq = 16*baud_rate / gcd(global_clock_freq, 16*baud_rate)
 * second register:
 * 	baud_limit = (global_clock_freq / 
 *                   gcd(global_clock_freq, 16*baud_rate)) - baud_freq
 */
module baud_gen(clk_i, rst_i, ce16_o, baud_freq_i, baud_limit_i);
input		clk_i;
input		rst_i;
output		ce16_o;
input [11:0]	baud_freq_i;
input [15:0]	baud_limit_i;

reg ce16_o;
reg [15:0] count;

always @(posedge clk_i or negedge rst_i)
begin
	if (!rst_i)
		count <= 16'h0;
	else if (count >= baud_limit_i)
		count <= count - baud_limit_i;
	else
		count <= count + baud_freq_i;
end

always @(posedge clk_i or negedge rst_i)
begin
	if (!rst_i)
		ce16_o <= 1'b0;
	else if (count >= baud_limit_i)
		ce16_o <= 1'b1;
	else
		ce16_o <= 1'b0;
end

endmodule

分频模块的仿真波形如下，上面是50M的输入时钟，下面是分频后的，需要注意的是，分频后的时钟的占空比不是1：1的，每一个9600Hz的周期中产生16个高电平，高电平维持一个20ns(50MHz的一个周期)

计算baud_freq和baud_limitC程序如下，程序中的输入频率clk_i为50MHZ，输出频率为9600*16。

#include <stdio.h>

int GCD(int a, int b)
{
        if (b == 0)
                return a;
        else
                return GCD(b, a%b);
}

int main()
{
        int clk_i = 50*1000*1000;
        int clk_o = 9600*16;

        int gcd = GCD(clk_i, clk_o);
        int baud_freq = clk_o/gcd;
        int baud_limit = (clk_i/gcd) - baud_freq;
        printf("baud_freq: 0x%x, baud_limit: 0x%x\n", baud_freq, baud_limit);
        return 0;
}

 

然后是发送模块：

module uart_tx(clk_i, 
		rst_i, 
		ce16_i, 
		ser_o, 
		tx_data_i, 
		new_tx_i, 
		tx_int_o, 
		tx_busy_o);
input		clk_i;
input		rst_i;
input		ce16_i;
output		ser_o;
input [7:0]	tx_data_i;
input		new_tx_i;
output		tx_int_o;
output		tx_busy_o;

reg		ser_o;
reg		tx_int_o;
reg		tx_busy_o;
reg [3:0]	count;
reg [3:0]	bit_count;
reg [8:0]	tx_data;

wire		ce1_end;
assign ce1_end = (count == 4'b1111) & ce16_i;

always @(posedge clk_i or negedge rst_i)
begin
	if (!rst_i)
		count <= 4'h0;
	else if (tx_busy_o & ce16_i)
		count <= count + 1'b1;
	else if (!tx_busy_o & ce16_i)
		count <= 1'b0;
end

always @(posedge clk_i or negedge rst_i)
begin
	if (!rst_i)
		tx_busy_o <= 1'b0;
	else if (!tx_busy_o & new_tx_i)
		tx_busy_o <= 1'b1;
	else if (tx_busy_o & ce1_end & (bit_count == 4'd9))
		tx_busy_o <= 1'b0;
end

always @(posedge clk_i or negedge rst_i)
begin
	if (!rst_i)
		bit_count <= 4'h0;
	else if (tx_busy_o & ce1_end)
		bit_count <= bit_count + 1'b1;
	else if (!tx_busy_o)
		bit_count <= 4'h0;
end

always @(posedge clk_i or negedge rst_i)
begin
	if (!rst_i)
		tx_data <= 9'h0;
	else if (!tx_busy_o)
		tx_data <= {tx_data_i, 1'b0};
	else if (tx_busy_o & ce1_end)
		tx_data <= {1'b1, tx_data[8:1]};
end

always @(posedge clk_i or negedge rst_i)
begin
	if (!rst_i)
		ser_o <= 1'b1;
	else if (tx_busy_o)
		ser_o <= tx_data[0];
	else
		ser_o <= 1'b1;
end


always @(posedge clk_i or negedge rst_i)
begin
	if (!rst_i)
		tx_int_o <= 1'b0;		
	else if (tx_busy_o & ce1_end & (bit_count == 4'd9))
		tx_int_o <= 1'b1;
	else
		tx_int_o <= 1'b0;
end

endmodule

接收模块：

module uart_rx(clk_i,
		rst_i,
		ce16_i,
		ser_i,
		rx_data_o,
		rx_int_o);
input		clk_i;
input		rst_i;
input		ce16_i;
input		ser_i;
output [7:0] 	rx_data_o;
output		rx_int_o;

reg [7:0] 	rx_data_o;
reg		rx_int_o;

reg [7:0] 	rx_data;
reg [1:0]	ser_in;
reg [3:0]	count;
reg [3:0]	bit_count;
reg		rx_busy;

wire		ce1_mid;
wire		ce1_end;

always @(posedge clk_i or negedge rst_i)
begin
	if (!rst_i)
		ser_in <= 2'b11;
	else
		ser_in <= {ser_in[0], ser_i};
end

always @(posedge clk_i or negedge rst_i)
begin
	if (!rst_i)
		count <= 4'h0;
	else if ((rx_busy | (ser_in[1] == 1'b0)) & ce16_i)
		count <= count + 1'b1;
	else if (!rx_busy & ce16_i)
		count <= 4'h0;
end

assign ce1_mid = ((count == 4'b0111) & ce16_i);
assign ce1_end = ((count == 4'b1111) & ce16_i);

always @(posedge clk_i or negedge rst_i)
begin
	if (!rst_i)
		rx_busy <= 1'b0;
	else if (!rx_busy & ce1_mid)
		rx_busy <= 1'b1;
	else if (rx_busy & ce1_end & (bit_count == 4'd9))
		rx_busy <= 1'b0;
end

always @(posedge clk_i or negedge rst_i)
begin
	if (!rst_i)
		bit_count <= 4'h0;
	else if (rx_busy & ce1_mid)
		bit_count <= bit_count + 1'b1;
	else if (!rx_busy)
		bit_count <= 4'h0;
end

always @(posedge clk_i or negedge rst_i)
begin
	if (!rst_i)
		rx_data <= 8'h0;
	else if (ce1_mid)
		rx_data <= {ser_in[1], rx_data[7:1]};
end

always @(posedge clk_i or negedge rst_i)
begin
	if (!rst_i) begin
		rx_data_o <= 8'h0;
		rx_int_o <= 1'b0;
	end else if (ce1_end & (bit_count == 4'd8)) begin
		rx_data_o <= rx_data;
		rx_int_o <= 1'b1;
	end else
		rx_int_o <= 1'b0;
end

endmodule

顶层模块：

module uart_loop_top(clk_i, rst_i, ser_i, ser_o);
input		clk_i;
input		rst_i;
input		ser_i;
output		ser_o;

// baud rate generator parameters for 9600 baud on 50MHz clock
`define D_BAUD_FREQ		12'h30
`define D_BAUD_LIMIT		16'h3CD9

wire		ce16;
wire [11:0]	baud_freq;
wire [15:0]	baud_limit; 

wire [7:0]	rx_data;
reg [7:0] 	rx_reg;
reg		start_tx;
wire		tx_int;
wire		tx_busy;

assign baud_freq = `D_BAUD_FREQ;
assign baud_limit = `D_BAUD_LIMIT;


baud_gen baud_gen1(.clk_i(clk_i), 
		.rst_i(rst_i), 
		.ce16_o(ce16),
		.baud_freq_i(baud_freq),
		.baud_limit_i(baud_limit));

uart_rx uart_rx1(.clk_i(clk_i), 
		.rst_i(rst_i),
		.ce16_i(ce16),
		.ser_i(ser_i),
		.rx_data_o(rx_data),
		.rx_int_o(rx_int));

uart_tx uart_tx1(.clk_i(clk_i),
		.rst_i(rst_i),
		.ce16_i(ce16),
		.ser_o(ser_o), 
		.tx_data_i(rx_reg),
		.new_tx_i(start_tx),
		.tx_int_o(tx_int),
		.tx_busy_o(tx_busy));

always @(posedge clk_i or negedge rst_i)
begin
	if (!rst_i)
		rx_reg <= 8'h0;
	else if (rx_int & ~tx_busy)
		rx_reg <= rx_data;
end


always @(posedge clk_i or negedge rst_i)
begin
	if (!rst_i)
		start_tx <= 1'b0;
	else if (rx_int & ~tx_busy)
		start_tx <= 1'b1;
	else
		start_tx <= 1'b0;
end

endmodule
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jim 说:
2014年4月28日 21:39

这里的串口时钟是一直开启的？

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2024年4月27日 19:15

When choosing an online casino game site, it's important to research and verify the site's reputation and safety. Look for sites that are licensed and regulated by recognized regulatory bodies, offer secure payment options, and have a responsive customer support team. Additionally, always gamble responsibly and within your means.


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