Pmod SSD Reference Manual

The Digilent Pmod SSD (Revision A) is a 2 digit seven-segment display commonly used to display a counter or timer.

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  • Two-digit high brightness seven-segment display
  • Easily view a counter or timer
  • Common Cathode configuration
  • Two 6-pin Pmod connectors with GPIO interfaces

Functional Description

The Pmod SSD utilizes a common cathode configuration to display a variety of LED segment combinations. The ten segment combinations corresponding to digits 0 - 9 are generally the most useful, although other custom combinations can also be created.

Interfacing with the Pmod

The Pmod SSD communicates with the host board via the GPIO protocol. A logic level high signal on a particular anode will light up that respective segment on whichever digit is currently enabled. Users are able to select a particular digit by driving the Digit Selection pin (C) to a logic high or low voltage.

Because only one digit can be lit at a particular time, users that want to use both digits to display a particular value will need to alternately light up the two digits at least every 20 milliseconds (50 Hz). This will correlate to each digit being lit up for 10 milliseconds each before the other segment needs to be “turned on”. Higher refresh rates can be achieved by alternating which digit is currently powered at shorter time intervals. Pmod SSD Block Diagram

Pinout Description Table

Header J1 Header J2
Pin Signal Description Pin Signal Description
1 AA Segment A 1 AE Segment E
2 AB Segment B 2 AF Segment F
3 AC Segment C 3 AG Segment G
4 AD Segment D 4 C Digit Selection pin
5 GND Power Supply Ground 5 GND Power Supply Ground
6 VCC Positive Power Supply 6 VCC Positive Power Supply

Segment locations on a SSD

Any external power applied to the Pmod SSD must be within 2.7V and 5.25V; however, it is recommended that Pmod is operated at 3.3V.

Physical Dimensions

The pins on the pin header are spaced 100 mil apart. The PCB is 1 inch long on the sides parallel to the pins on the pin header and 1.7 inches long on the sides perpendicular to the pin header.

Additional Information

The schematics of the Pmod SSD are available here.

Example code demonstrating how to get information from the Pmod SSD can be found here.

If you have any questions or comments about the Pmod SSD, feel free to post them under the appropriate section (“Add-on Boards”) of the Digilent Forum.