Subversion Repositories uart2bus

//---------------------------------------------------------------------------------------

// uart receive module  

//

//---------------------------------------------------------------------------------------

module uart_rx

(

        clock, reset,

        ce_16, ser_in,

        rx_data, new_rx_data

);

//---------------------------------------------------------------------------------------

// modules inputs and outputs 

input                   clock;                  // global clock input 

input                   reset;                  // global reset input 

input                   ce_16;                  // baud rate multiplyed by 16 - generated by baud module 

input                   ser_in;                 // serial data input 

output  [7:0]    rx_data;                // data byte received 

output                  new_rx_data;    // signs that a new byte was received 

// internal wires 

wire ce_1;              // clock enable at bit rate 

wire ce_1_mid;  // clock enable at the middle of each bit - used to sample data 

// internal registers 

reg     [7:0] rx_data;

reg     new_rx_data;

reg [1:0] in_sync;

reg rx_busy;

reg [3:0]        count16;

reg [3:0]        bit_count;

reg [7:0]        data_buf;

//---------------------------------------------------------------------------------------

// module implementation 

// input async input is sampled twice 

always @ (posedge clock or posedge reset)

begin

        if (reset)

                in_sync <= 2'b11;

        else

                in_sync <= {in_sync[0], ser_in};

end

// a counter to count 16 pulses of ce_16 to generate the ce_1 and ce_1_mid pulses.

// this counter is used to detect the start bit while the receiver is not receiving and 

// signs the sampling cycle during reception. 

always @ (posedge clock or posedge reset)

begin

        if (reset)

                count16 <= 4'b0;

        else if (ce_16)

        begin

                if (rx_busy | (in_sync[1] == 1'b0))

                        count16 <= count16 + 4'b1;

                else

                        count16 <= 4'b0;

        end

end

// ce_1 pulse indicating expected end of current bit 

assign ce_1 = (count16 == 4'b1111) & ce_16;

// ce_1_mid pulse indication the sampling clock cycle of the current data bit 

assign ce_1_mid = (count16 == 4'b0111) & ce_16;

// receiving busy flag 

always @ (posedge clock or posedge reset)

begin

        if (reset)

                rx_busy <= 1'b0;

        else if (~rx_busy & ce_1_mid)

                rx_busy <= 1'b1;

        else if (rx_busy & (bit_count == 4'h9) & ce_1)

                rx_busy <= 1'b0;

end

// bit counter 

always @ (posedge clock or posedge reset)

begin

        if (reset)

                bit_count <= 4'h0;

        else if (~rx_busy)

                bit_count <= 4'h0;

        else if (rx_busy & ce_1_mid)

                bit_count <= bit_count + 4'h1;

end

// data buffer shift register 

always @ (posedge clock or posedge reset)

begin

        if (reset)

                data_buf <= 8'h0;

        else if (rx_busy & ce_1_mid)

                data_buf <= {in_sync[1], data_buf[7:1]};

end

// data output and flag 

always @ (posedge clock or posedge reset)

begin

        if (reset)

        begin

                rx_data <= 8'h0;

                new_rx_data <= 1'b0;

        end

        else if (rx_busy & (bit_count == 4'h8) & ce_1)

        begin

                rx_data <= data_buf;

                new_rx_data <= 1'b1;

        end

        else

                new_rx_data <= 1'b0;

end

endmodule

//---------------------------------------------------------------------------------------

//                                              Th.. Th.. Th.. Thats all folks !!!

//---------------------------------------------------------------------------------------