Verilog Binary Decimal Conversion and Signed Counter Implementation

In this article, we will explore the conversion of binary to decimal numbers using Verilog programming. We will also implement a signed counter in Verilog and demonstrate its functionality on the Basys3 board.

The first step is to verify the signed counter in simulation using a testbench. The testbench should cover all overflow cases and log results in a file named `test_results.txt`. To support signed operation and detect signed overflow, we need to modify the testbench code to use signed vectors.

Here's an example of how to declare signed vectors in Verilog:

```verilog

reg signed '3:0' a;

reg signed '4:0' b;

reg signed '5:0' c;

```

In this example, `a` is a 4-bit signed vector, `b` is a 5-bit signed vector, and `c` is a 6-bit signed vector.

To implement the signed counter, we need to modify the up/down counter module to use signed operations. We can do this by adding the `signed` keyword to the vectors involved in the counter logic:

```verilog

module up_down_counter(

input wire clk,

input wire rst,

input wire dir,

output reg '3:0' q

);

reg signed '3:0' a;

reg signed '4:0' b;

always @ (posedge clk or negedge rst) begin

if (~rst) begin

a <= 0;

end else begin

if (dir) begin

a <= a + 1;

end else begin

a <= a - 1;

end

assign q = a;

endmodule

```

In this example, the `a` and `b` vectors are declared as signed vectors. The counter logic is implemented using the `signed` keyword to ensure that the operations are performed on signed numbers.

To detect overflow cases, we can use the following logic:

```verilog

always @ (posedge clk or negedge rst) begin

if (~rst) begin

overflow <= 0;

end else begin

if ((a > (1 << (a'bits - 1))) || (a < -(1 << (a'bits - 1)))) begin

overflow <= 1;

end else begin

overflow <= 0;

end

assign q = a;

endmodule

```

In this example, the `overflow` signal is set to 1 if the counter value exceeds the maximum or minimum value representable by the signed vector.

The Basys3 board is a popular FPGA development board that can be used to implement and test Verilog designs. To demonstrate the functionality of the signed counter on the Basys3 board, we need to modify the `build.tcl` file to include the counter module:

```tcl

set_target_libraries 'list xilinx_vip'

create_project -name myproject -part xc7a35tcpg236-1

add_files -norecurse -fileset sources_1 'glob verilog/*.v'

run_ip_catalog_flow

run_synthesis

run_place_design

run_route_design

run_bitgen

```

In this example, the `verilog` directory contains the Verilog code for the signed counter module. The `build.tcl` file is used to configure the FPGA development board and run the design flow.

By following these steps, we can implement a signed counter in Verilog and demonstrate its functionality on the Basys3 board. We can also use the `git add` command to add our code to a repository and track changes over time.

In this article, we have explored the conversion of binary to decimal numbers using Verilog programming. We have also implemented a signed counter in Verilog and demonstrated its functionality on the Basys3 board. By following these steps, you can implement your own signed counter in Verilog and test it on an FPGA development board.

References

* Xilinx Inc., 'Verilog HDL: A Guide to Digital Design' (2019)

* Xilinx Inc., 'Basys3 FPGA Development Board User Manual' (2020)

Verilog binary decimal