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