CAN Controller in Verilog

CAN Transmitter


module can_tx (
    input wire clk,               // System clock
    input wire reset,             // Reset signal
    input wire [10:0] identifier, // CAN identifier
    input wire [7:0] data,        // Data to transmit
    input wire start_tx,          // Start transmission signal
    output reg tx,                // CAN transmit line
    output reg busy,              // Transmission busy flag
    output reg done               // Transmission done flag
);
    // States
    parameter IDLE = 2'b00,
              SEND_START = 2'b01,
              SEND_DATA = 2'b10,
              SEND_END = 2'b11;

    reg [1:0] state;              // State machine state
    reg [3:0] bit_cnt;            // Bit counter

    always @(posedge clk or posedge reset) begin
        if (reset) begin
            state <= IDLE;
            tx <= 1'b1;            // Idle state is high
            busy <= 1'b0;
            done <= 1'b0;
            bit_cnt <= 4'b0;
        end else begin
            case (state)
                IDLE: begin
                    done <= 1'b0;
                    if (start_tx) begin
                        busy <= 1'b1;
                        state <= SEND_START;
                        bit_cnt <= 4'b0; // Reset bit counter
                    end
                end

                SEND_START: begin
                    // Transmit Start of Frame (SOF)
                    tx <= 1'b0; // Start bit (dominant)
                    state <= SEND_DATA;
                end

                SEND_DATA: begin
                    if (bit_cnt < 8) begin
                        tx <= data[bit_cnt]; // Send data
                        bit_cnt <= bit_cnt + 1;
                    end else begin
                        state <= SEND_END; // Move to end of frame
                    end
                end

                SEND_END: begin
                    // Transmit End of Frame (EOF)
                    tx <= 1'b1; // End bit (recessive)
                    busy <= 1'b0;
                    done <= 1'b1; // Transmission done
                    state <= IDLE; // Go back to idle
                end

                default: state <= IDLE; // Default to idle
            endcase
        end
    end
endmodule

CAN Receiver (Simplified)


module can_rx (
    input wire clk,               // System clock
    input wire reset,             // Reset signal
    input wire rx,                // CAN receive line
    output reg [10:0] identifier, // Received CAN identifier
    output reg [7:0] data,        // Received data
    output reg data_ready,        // Data ready signal
    output reg busy               // Receiver busy flag
);
    // States
    parameter IDLE = 2'b00,
              RECEIVE_START = 2'b01,
              RECEIVE_DATA = 2'b10,
              RECEIVE_END = 2'b11;

    reg [1:0] state;              // State machine state
    reg [3:0] bit_cnt;            // Bit counter

    always @(posedge clk or posedge reset) begin
        if (reset) begin
            state <= IDLE;
            data_ready <= 1'b0;
            busy <= 1'b0;
            bit_cnt <= 4'b0;
        end else begin
            case (state)
                IDLE: begin
                    data_ready <= 1'b0;
                    if (rx == 1'b0) begin // Start bit detected
                        busy <= 1'b1;
                        state <= RECEIVE_START;
                        bit_cnt <= 4'b0; // Reset bit counter
                    end
                end

                RECEIVE_START: begin
                    // Wait for data
                    state <= RECEIVE_DATA;
                end

                RECEIVE_DATA: begin
                    if (bit_cnt < 8) begin
                        data[bit_cnt] <= rx; // Receive data
                        bit_cnt <= bit_cnt + 1;
                    end else begin
                        state <= RECEIVE_END; // Move to end of frame
                    end
                end

                RECEIVE_END: begin
                    // Handle end of frame
                    data_ready <= 1'b1; // Indicate data is ready
                    busy <= 1'b0;
                    state <= IDLE; // Go back to idle
                end

                default: state <= IDLE; // Default to idle
            endcase
        end
    end
endmodule