Generic binary to 7segment

This post is about my GitLab project Binary to 7segment.
It’s a generic 7-segment display driver constructed like image below, as its name implies it’s going to take N-bit binary and output 7-segment equivalent numbers by multiplexing each segment automatically.

You must set number of bits in binary input (BINARY_WIDTH) and number of 7-segment display digits (DISPLAY_NUMBER) and whether it is common anode or not (COMMON_ANODE).

binary_to_7segment.vhdl consists of four modules, each one will be explained separately.

module binary to bcd

In binary_to_bcd.vhdl, you declare number of bits in binary by using BINARY_WIDTH and number of equivalent BCD digits by using TOTAL_BCD_DIGIT.

• The module uses the double dabble algorithm¹ to convert binary into BCD in the following way:
  1. initializes the variables
  2. checks if BCD digit is greater than four if so then adds three to it
  3. shifts BCD left and copy MSB of binary input to BCD LSB
  4. shifts binary input left by 1 bit
     the above steps will be repeated for each bit of binary input

Module output (bcd_out) goes into generic mux to select each BCD digit for conversion.

module generic mux

generic_mux.vhdl² is a generic multiplexer of TOTAL_MUX_INPUT input of N_BIT_MUX wide each and output of N_BIT_MUX wide.

In order to make a generic mux from STD_LOGIC_VECTOR type, the function slv_to_generic_mux_type is used.

The generic mux select pins (mux_select) that are driven by common pin selector are used for multiplexing BCD digits in order to convert them to 7-segment digits.

module bcd to 7segment

The bcd_to_7segment.vhdl converts a 4-bit BCD digit to 7-bit 7-segment pins and chooses 7-segment type, Whether it is a common anode or cathode (COMMON_ANODE).

The selected assignment uses a common anode configuration.
The MSB of the module’s output is the G segment and its LSB is the A segment.

The last assignment just not the selected assignment data if COMMON_ANODE is false for common cathode 7-segment displays.

module common pin selector

The module is common_pin_selector.vhdl.

mux_select output is responsible for multiplexing 7-segment digits using generic mux while simultaneously generating DISPLAY_NUMBER common pin signals.

The first part of the module is a counter that increases at every rising edge of the multiplexing_clock for mux_select output.

The second part is a ring counter³ for common_pins_out that one bit is active at a time (it depends on COMMON_ANODE whether the bit is zero or one).

count up 7segment (example)

• The example has three more generics:

  • DEBOUNCE_CLOCK_DIVIDER: divide input clock by 2^N for clock of the module that debouches the button when you press it.

  • MULTIPLEXING_CLOCK_DIVIDER: divide input clock by 2^N for 7-segment display multiplexing speed.

  • COUNT_TO: maximum number that will be displayed on 7-segment display.

It’s an example of generating digits from zero up to COUNT_TO and cycle again using ascending_binary_generator.vhdl which is a counter.

There are two counters for generating clocks for other modules:

• debounce_clock_generator.vhdl for denouncing³ the push_button in push_button_debounce.vhdl and
• multiplexing_clock_generator.vhdl for multiplexing the 7-segment displays in common pin selector.

There are two testbenches:

• count_up_7segment_tb.vhd checks if four 7-segment digits (seven_segment_out) and common_pins_out have correct values only for common anode.
• count_up_7segment_tb_2.vhd checks if is the number of buttons pressed displayed correctly on each 7-segment digit at the respective common_pins_out.

References