==========================================================================
//-----------------------------------------------------
// Design Name : uart
// File Name?? : uart.v
// Function??? : Simple UART
// Coder?????? : Deepak Kumar Tala
//-----------------------------------------------------
module uart (
reset????????? ,
txclk????????? ,
ld_tx_data???? ,
tx_data??????? ,
tx_enable????? ,
tx_out???????? ,
tx_empty?????? ,
rxclk????????? ,
uld_rx_data??? ,
rx_data??????? ,
rx_enable????? ,
rx_in????????? ,
rx_empty
);
// Port declarations
input??????? reset????????? ;
input??????? txclk????????? ;
input??????? ld_tx_data???? ;
input [7:0] tx_data??????? ;
input??????? tx_enable????? ;
output?????? tx_out???????? ;
output?????? tx_empty?????? ;
input??????? rxclk????????? ;
input??????? uld_rx_data??? ;
output [7:0] rx_data??????? ;
input??????? rx_enable????? ;
input??????? rx_in????????? ;
output?????? rx_empty?????? ;

// Internal Variables
reg [7:0]??? tx_reg???????? ;
reg????????? tx_empty?????? ;
reg????????? tx_over_run??? ;
reg [3:0]??? tx_cnt???????? ;
reg????????? tx_out???????? ;
reg [7:0]??? rx_reg???????? ;
reg [7:0]??? rx_data??????? ;
reg [3:0]??? rx_sample_cnt ;
reg [3:0]??? rx_cnt???????? ;
reg????????? rx_frame_err?? ;
reg????????? rx_over_run??? ;
reg????????? rx_empty?????? ;
reg????????? rx_d1????????? ;
reg????????? rx_d2????????? ;
reg????????? rx_busy??????? ;

// UART RX Logic
always @ (posedge rxclk or posedge reset)
if (reset) begin
rx_reg??????? <= 0;
rx_data?????? <= 0;
rx_sample_cnt <= 0;
rx_cnt??????? <= 0;
rx_frame_err <= 0;
rx_over_run?? <= 0;
rx_empty????? <= 1;
rx_d1???????? <= 1;
rx_d2???????? <= 1;
rx_busy?????? <= 0;
end else begin
// Synchronize the asynch signal
rx_d1 <= rx_in;
rx_d2 <= rx_d1;
// Uload the rx data
if (uld_rx_data) begin
??? rx_data <= rx_reg;
??? rx_empty <= 1;
end
// Receive data only when rx is enabled
if (rx_enable) begin
??? // Check if just received start of frame
??? if (!rx_busy && !rx_d2) begin
????? rx_busy?????? <= 1;
????? rx_sample_cnt <= 1;
????? rx_cnt??????? <= 0;
??? end
??? // Start of frame detected, Proceed with rest of data
??? if (rx_busy) begin
?????? rx_sample_cnt <= rx_sample_cnt + 1;
?????? // Logic to sample at middle of data
?????? if (rx_sample_cnt == 7) begin
????????? if ((rx_d2 == 1) && (rx_cnt == 0)) begin
??????????? rx_busy <= 0;
????????? end else begin
??????????? rx_cnt <= rx_cnt + 1;
??????????? // Start storing the rx data
??????????? if (rx_cnt > 0 && rx_cnt < 9) begin
????????????? rx_reg[rx_cnt - 1] <= rx_d2;
??????????? end
??????????? if (rx_cnt == 9) begin
?????????????? rx_busy <= 0;
?????????????? // Check if End of frame received correctly
?????????????? if (rx_d2 == 0) begin
???????????????? rx_frame_err <= 1;
?????????????? end else begin
???????????????? rx_empty???? <= 0;
???????????????? rx_frame_err <= 0;
???????????????? // Check if last rx data was not unloaded,
???????????????? rx_over_run <= (rx_empty) ? 0 : 1;
?????????????? end
??????????? end
????????? end
?????? end
??? end
end
if (!rx_enable) begin
??? rx_busy <= 0;
end
end

// UART TX Logic
always @ (posedge txclk or posedge reset)
if (reset) begin
tx_reg??????? <= 0;
tx_empty????? <= 1;
tx_over_run?? <= 0;
tx_out??????? <= 1;
tx_cnt??????? <= 0;
end else begin
?? if (ld_tx_data) begin
????? if (!tx_empty) begin
??????? tx_over_run <= 0;
????? end else begin
??????? tx_reg?? <= tx_data;
??????? tx_empty <= 0;
????? end
?? end
?? if (tx_enable && !tx_empty) begin
???? tx_cnt <= tx_cnt + 1;
???? if (tx_cnt == 0) begin
?????? tx_out <= 0;
???? end
???? if (tx_cnt > 0 && tx_cnt < 9) begin
??????? tx_out <= tx_reg[tx_cnt -1];
???? end
???? if (tx_cnt == 9) begin
?????? tx_out <= 1;
?????? tx_cnt <= 0;
?????? tx_empty <= 1;
???? end
?? end
?? if (!tx_enable) begin
???? tx_cnt <= 0;
?? end
end

endmodule

出自http://www.asic-world.com/，測試過了很好用。