software
https://realterm.sourceforge.io/
// 需 Import pin assignments DE2_115_pin_assignments
module ASYNC(
input CLOCK_50, // 50 MHz clock
input [3:0] KEY, // Pushbutton[3:0]
input [17:0] SW, // Toggle Switch[17:0]
output [6:0] HEX0,HEX1,HEX2,HEX3,HEX4,HEX5,HEX6,HEX7, // Seven Segment Digits
output [8:0] LEDG, // LED Green
output [17:0] LEDR, // LED Red
input UART_RXD,
output UART_TXD
);
// blank unused 7-segment digits
assign HEX0 = 7'b111_1111;
assign HEX1 = 7'b111_1111;
assign HEX2 = 7'b111_1111;
assign HEX3 = 7'b111_1111;
assign HEX4 = 7'b111_1111;
assign HEX5 = 7'b111_1111;
assign HEX6 = 7'b111_1111;
assign HEX7 = 7'b111_1111;
//assign LEDR[7:0]=SW[7:0];
//assign LEDR[17]=myclock[1];
//serialGPIO(input clk,input RxD, output TxD,output reg [7:0] GPout, // general purpose outputs
// input [7:0] GPin // general purpose inputs
serialGPIO(CLOCK_50,UART_RXD,UART_TXD,LEDG[7:0], // general purpose outputs
SW[7:0]); // general purpose inputs
endmodule
//=============================================
module serialGPIO(
input clk,
input RxD,
output TxD,
output reg [7:0] GPout, // general purpose outputs
input [7:0] GPin // general purpose inputs
);
wire RxD_data_ready;
wire [7:0] RxD_data;
async_receiver RX(.clk(clk), .RxD(RxD), .RxD_data_ready(RxD_data_ready), .RxD_data(RxD_data));
always @(posedge clk) if(RxD_data_ready) GPout <= RxD_data;
async_transmitter TX(.clk(clk), .TxD(TxD), .TxD_start(RxD_data_ready), .TxD_data(GPin));
endmodule
//================================================
////////////////////////////////////////////////////////
// RS-232 RX and TX module
// (c) fpga4fun.com & KNJN LLC - 2003 to 2016
// The RS-232 settings are fixed
// TX: 8-bit data, 2 stop, no-parity
// RX: 8-bit data, 1 stop, no-parity (the receiver can accept more stop bits of course)
//`define SIMULATION // in this mode, TX outputs one bit per clock cycle
// and RX receives one bit per clock cycle (for fast simulations)
////////////////////////////////////////////////////////
module async_transmitter(
input clk,
input TxD_start,
input [7:0] TxD_data,
output TxD,
output TxD_busy
);
// Assert TxD_start for (at least) one clock cycle to start transmission of TxD_data
// TxD_data is latched so that it doesn't have to stay valid while it is being sent
parameter ClkFrequency = 50_000_000; // 25MHz
//parameter Baud = 115200;
parameter Baud = 4800;
generate
if(ClkFrequency<Baud*8 && (ClkFrequency % Baud!=0)) ASSERTION_ERROR PARAMETER_OUT_OF_RANGE("Frequency incompatible with requested Baud rate");
endgenerate
////////////////////////////////
`ifdef SIMULATION
wire BitTick = 1'b1; // output one bit per clock cycle
`else
wire BitTick;
BaudTickGen #(ClkFrequency, Baud) tickgen(.clk(clk), .enable(TxD_busy), .tick(BitTick));
`endif
reg [3:0] TxD_state = 0;
wire TxD_ready = (TxD_state==0);
assign TxD_busy = ~TxD_ready;
reg [7:0] TxD_shift = 0;
always @(posedge clk)
begin
if(TxD_ready & TxD_start)
TxD_shift <= TxD_data;
else
if(TxD_state[3] & BitTick)
TxD_shift <= (TxD_shift >> 1);
case(TxD_state)
4'b0000: if(TxD_start) TxD_state <= 4'b0100;
4'b0100: if(BitTick) TxD_state <= 4'b1000; // start bit
4'b1000: if(BitTick) TxD_state <= 4'b1001; // bit 0
4'b1001: if(BitTick) TxD_state <= 4'b1010; // bit 1
4'b1010: if(BitTick) TxD_state <= 4'b1011; // bit 2
4'b1011: if(BitTick) TxD_state <= 4'b1100; // bit 3
4'b1100: if(BitTick) TxD_state <= 4'b1101; // bit 4
4'b1101: if(BitTick) TxD_state <= 4'b1110; // bit 5
4'b1110: if(BitTick) TxD_state <= 4'b1111; // bit 6
4'b1111: if(BitTick) TxD_state <= 4'b0010; // bit 7
4'b0010: if(BitTick) TxD_state <= 4'b0011; // stop1
4'b0011: if(BitTick) TxD_state <= 4'b0000; // stop2
default: if(BitTick) TxD_state <= 4'b0000;
endcase
end
assign TxD = (TxD_state<4) | (TxD_state[3] & TxD_shift[0]); // put together the start, data and stop bits
endmodule
//======================================================
////////////////////////////////////////////////////////
module async_receiver(
input clk,
input RxD,
output reg RxD_data_ready = 0,
output reg [7:0] RxD_data = 0, // data received, valid only (for one clock cycle) when RxD_data_ready is asserted
// We also detect if a gap occurs in the received stream of characters
// That can be useful if multiple characters are sent in burst
// so that multiple characters can be treated as a "packet"
output RxD_idle, // asserted when no data has been received for a while
output reg RxD_endofpacket = 0 // asserted for one clock cycle when a packet has been detected (i.e. RxD_idle is going high)
);
parameter ClkFrequency = 50_000_000; // 25MHz
//parameter Baud = 115200;
parameter Baud = 4800;
parameter Oversampling = 8; // needs to be a power of 2
// we oversample the RxD line at a fixed rate to capture each RxD data bit at the "right" time
// 8 times oversampling by default, use 16 for higher quality reception
generate
if(ClkFrequency<Baud*Oversampling) ASSERTION_ERROR PARAMETER_OUT_OF_RANGE("Frequency too low for current Baud rate and oversampling");
if(Oversampling<8 || ((Oversampling & (Oversampling-1))!=0)) ASSERTION_ERROR PARAMETER_OUT_OF_RANGE("Invalid oversampling value");
endgenerate
////////////////////////////////
reg [3:0] RxD_state = 0;
`ifdef SIMULATION
wire RxD_bit = RxD;
wire sampleNow = 1'b1; // receive one bit per clock cycle
`else
wire OversamplingTick;
BaudTickGen #(ClkFrequency, Baud, Oversampling) tickgen(.clk(clk), .enable(1'b1), .tick(OversamplingTick));
// synchronize RxD to our clk domain
reg [1:0] RxD_sync = 2'b11;
always @(posedge clk) if(OversamplingTick) RxD_sync <= {RxD_sync[0], RxD};
// and filter it
reg [1:0] Filter_cnt = 2'b11;
reg RxD_bit = 1'b1;
always @(posedge clk)
if(OversamplingTick)
begin
if(RxD_sync[1]==1'b1 && Filter_cnt!=2'b11) Filter_cnt <= Filter_cnt + 1'd1;
else
if(RxD_sync[1]==1'b0 && Filter_cnt!=2'b00) Filter_cnt <= Filter_cnt - 1'd1;
if(Filter_cnt==2'b11) RxD_bit <= 1'b1;
else
if(Filter_cnt==2'b00) RxD_bit <= 1'b0;
end
// and decide when is the good time to sample the RxD line
function integer log2(input integer v); begin log2=0; while(v>>log2) log2=log2+1; end endfunction
localparam l2o = log2(Oversampling);
reg [l2o-2:0] OversamplingCnt = 0;
always @(posedge clk) if(OversamplingTick) OversamplingCnt <= (RxD_state==0) ? 1'd0 : OversamplingCnt + 1'd1;
wire sampleNow = OversamplingTick && (OversamplingCnt==Oversampling/2-1);
`endif
// now we can accumulate the RxD bits in a shift-register
always @(posedge clk)
case(RxD_state)
4'b0000: if(~RxD_bit) RxD_state <= `ifdef SIMULATION 4'b1000 `else 4'b0001 `endif; // start bit found?
4'b0001: if(sampleNow) RxD_state <= 4'b1000; // sync start bit to sampleNow
4'b1000: if(sampleNow) RxD_state <= 4'b1001; // bit 0
4'b1001: if(sampleNow) RxD_state <= 4'b1010; // bit 1
4'b1010: if(sampleNow) RxD_state <= 4'b1011; // bit 2
4'b1011: if(sampleNow) RxD_state <= 4'b1100; // bit 3
4'b1100: if(sampleNow) RxD_state <= 4'b1101; // bit 4
4'b1101: if(sampleNow) RxD_state <= 4'b1110; // bit 5
4'b1110: if(sampleNow) RxD_state <= 4'b1111; // bit 6
4'b1111: if(sampleNow) RxD_state <= 4'b0010; // bit 7
4'b0010: if(sampleNow) RxD_state <= 4'b0000; // stop bit
default: RxD_state <= 4'b0000;
endcase
always @(posedge clk)
if(sampleNow && RxD_state[3]) RxD_data <= {RxD_bit, RxD_data[7:1]};
//reg RxD_data_error = 0;
always @(posedge clk)
begin
RxD_data_ready <= (sampleNow && RxD_state==4'b0010 && RxD_bit); // make sure a stop bit is received
//RxD_data_error <= (sampleNow && RxD_state==4'b0010 && ~RxD_bit); // error if a stop bit is not received
end
`ifdef SIMULATION
assign RxD_idle = 0;
`else
reg [l2o+1:0] GapCnt = 0;
always @(posedge clk) if (RxD_state!=0) GapCnt<=0; else if(OversamplingTick & ~GapCnt[log2(Oversampling)+1]) GapCnt <= GapCnt + 1'h1;
assign RxD_idle = GapCnt[l2o+1];
always @(posedge clk) RxD_endofpacket <= OversamplingTick & ~GapCnt[l2o+1] & &GapCnt[l2o:0];
`endif
endmodule
//============================================================
////////////////////////////////////////////////////////
module BaudTickGen(
input clk, enable,
output tick // generate a tick at the specified baud rate * oversampling
);
parameter ClkFrequency = 50_000_000;
//parameter Baud = 115200;
parameter Baud = 4800;
parameter Oversampling = 1;
function integer log2(input integer v); begin log2=0; while(v>>log2) log2=log2+1; end endfunction
localparam AccWidth = log2(ClkFrequency/Baud)+8; // +/- 2% max timing error over a byte
reg [AccWidth:0] Acc = 0;
localparam ShiftLimiter = log2(Baud*Oversampling >> (31-AccWidth)); // this makes sure Inc calculation doesn't overflow
localparam Inc = ((Baud*Oversampling << (AccWidth-ShiftLimiter))+(ClkFrequency>>(ShiftLimiter+1)))/(ClkFrequency>>ShiftLimiter);
always @(posedge clk) if(enable) Acc <= Acc[AccWidth-1:0] + Inc[AccWidth:0]; else Acc <= Inc[AccWidth:0];
assign tick = Acc[AccWidth];
endmodule
////////////////////////////////////////////////////////
////////////////////////////////////////////////////////
// dummy module used to be able to raise an assertion in Verilog
module ASSERTION_ERROR();
endmodule
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