**Button and Digital Tube Display**
A LED digital display (LED Segment Displays) is a device that consists of multiple light-emitting diodes (LEDs) arranged in an "8" shape. These LEDs are internally connected, and to activate the desired segments, you only need to connect the corresponding strokes and common electrodes. The most commonly used types have 7 segments plus a decimal point, while others may include additional features such as half digits, 1, 2, 3, 4, 5, 6, 8, 10, and more. Based on the connection method of the LEDs, these displays can be categorized into two types: common cathode and common anode. Understanding these characteristics is crucial because different types of digital tubes not only require different hardware circuits but also different programming approaches. Figure 2 shows the internal circuit diagrams for both common cathode and common anode digital tubes. Their illumination principle is similar, with the main difference being the polarity of the power supply. The available colors include red, green, blue, yellow, and others.
Figure 1: This is a 10-pin 7-segment LED digital tube with a decimal point.
Figure 2: Pin definition.
The following section describes the implementation of an FPGA-based program for controlling a digital tube display using buttons:
```verilog
module key_led(clk_50M, key, duan_ma, wei_ma);
input clk_50M;
input [3:0] key; // Key code input
output [3:0] wei_ma; // Digit selection signal
output [7:0] duan_ma; // Segment code output
wire [3:0] key;
reg [7:0] duan_ma;
reg [3:0] wei_ma;
reg [3:0] key_temp;
always @(posedge clk_50M) begin
key_temp <= key; // Store key value
case (key_temp)
4'b0111: duan_ma <= 8'b11000000; // Display '0'
4'b1011: duan_ma <= 8'b10010000; // Display '9'
4'b1101: duan_ma <= 8'b10000010; // Display '6'
4'b1110: duan_ma <= 8'b10110000; // Display '3'
endcase
end
always @(posedge clk_50M) begin
case (key_temp)
4'b0111: wei_ma <= 4'b0111; // Select digit position
4'b1011: wei_ma <= 4'b1011;
4'b1101: wei_ma <= 4'b1101;
4'b1110: wei_ma <= 4'b1110;
endcase
end
endmodule
```
This module controls the digital tube display based on the key pressed. Each key corresponds to a specific segment code and selects the appropriate digit position.
For static display of numbers 0–7, here's another module:
```verilog
module led_0_7(clk, rst, dataout, en);
input clk, rst;
output [7:0] dataout; // Segment code output
output [7:0] en; // Digit enable output
reg [7:0] dataout;
reg [7:0] en;
reg [15:0] cnt_scan; // Scan frequency counter
reg [4:0] dataout_buf;
always @(posedge clk or negedge rst) begin
if (!rst) begin
cnt_scan <= 0;
end else begin
cnt_scan <= cnt_scan + 1;
end
end
endmodule
```
This module provides a static display of digits 0 through 7 by setting the appropriate segment codes and enabling the correct digit position. It ensures stable and clear display of numbers on the LED digital tube.
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