7-Segment Display Menu

test.mp4

Alphanumeric custom messages on 7-Segment Display Menu using Boolean Board
with integrated 8 x 7-segment displays and 4 button menu.

Key Features

• Dual clock synchronization
• Four-state display control logic
• Dynamic symbol selection and addressing
• Safe initialization avoiding undefined states
• Efficient right-to-left digit scanning

RTL Netlist

Netlist generated by Vivado v2024.1 (64-bit)

seg_driver Module

The seg_driver module features two clock signals for synchronization purposes and operates based on four states:

1. Select symbol
2. Display symbol on screen
3. Change digit
4. Turn off the display

Overview

This module includes a 40-bit input called word and an 8-bit input called out_sym, which is connected to a 32-bit memory (M0). Additionally, there is a single 5-bit output named sel_sym, which is also connected to memory M0. This output acts as the address sent to the memory so that it can provide the corresponding word through the previously mentioned out_sym input.

Logic Breakdown

The code logic can be divided into four main parts:

1. Initialize Variables

An initial statement assigns starting values to all registers, leaving the circuit in a known state — in this case, with the display completely turned off. This ensures that no floating registers with ambiguous values exist, which could lead to unknown (X) or high-impedance (Z) states.

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2. Select the Symbol

A case statement checks the state of the variable sel_digit, which indicates which digit of the two 4-digit 7-segment modules is currently active. The corresponding symbol is then taken from the 40-bit word register.

For example: If sel_digit = 3, the module will select the fourth group of 5 bits (bits 15 to 19) from the word. This group is used as the address sent to the 32-bit memory, which then provides the corresponding character via the out_sym output.

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3. Display on Screen

Using the same case statement, the sel_digit variable determines which digit to display. Depending on the selected digit, the symbol stored in memory (out_sym) is assigned and shown on screen. Only one digit is turned on per cycle, and it is turned off before the cycle ends.

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4. Change Digit

Conditional statements increment the sel_digit variable by 1 until it reaches its maximum value (7). After that, it resets back to 0.

This means the display performs a right-to-left sweep, updating the 7-segment display as many times as the combined period of both clocks allows. In other words, the display refreshes at the same frequency as the slowest clock.

Summary

Signal	Type	Width	Description
word	Input	40 bits	Input data containing encoded symbol addresses
out_sym	Input	8 bits	Symbol data retrieved from 32-bit memory (M0)
sel_sym	Output	5 bits	Memory address used to fetch symbols
sel_digit	Internal	3 bits	Current digit being displayed (0–7)

Typical Hello World message displayed in Spanish

Mealy State Machine