Open Source Pmod Designs

August 23, 2020 - sam210723

The Pmod Standard developed by Digilent is a peripheral protocol, interconnect and form-factor guideline supported by various FPGA and microcontroller development boards. Digilent manufacture a wide variety of modules which conform to the Pmod standard. Some development boards which support the standard are listed below.

Board	Manufacturer	FPGA	Price	Buy
iCESugar	MuseLab	Lattice ICE40UP5K	$35 USD	MuseLab AliExpress Store
Mimas V2	Numato Lab	Xilinx XC6SLX9	$50 USD	Numato Lab Store
iCEBreaker	1BitSquared	Lattice iCE40UP5K	$65 USD	1BitSquared Store
ULX3S	Radiona	Lattice LFE5U-12F / LFE5U-85F	$115 / $155 USD	Radiona Crowd Supply Store
ECPIX-5	LambdaConcept	Lattice LFE5U-45F / LFE5U-85F	€99 / €149	LambdaConcept Store
Arty A7	Digilent	Xilinx XC7A35T / XC7A100T	$129 / $249 USD	Digilent Store

Designs

	SFP Pmod Interface for Small Form-factor Pluggable (SFP) modules
	TOSLINK Pmod Interface for the TOSLINK fibre optic connector
	Raspberry Pi Pico Pmod Adaptor Connect Pmods to a Raspberry Pi Pico microcontroller

Small Form-factor Pluggable (SFP) Pmod

Small Form-factor Pluggable (SFP) transceivers typically convert bi-directional electrical signalling to a pair of optical fibres for transmission over long distances. These modules are commonly found in telecommunications and networking applications where they carry various protocols including Ethernet and Fibre Channel.

The Pmod standard assumes a maximum current draw per Pmod of 100mA. Check your development board is capable of supplying the required current through the Pmod connectors before plugging in a SFP module.

Downloads

The PCB is a 4-layer impedance controlled board which uses the JLC7628 stackup and JLCPCB design rules. Project files and gerbers were built with Autodesk EAGLE 9.6.2.

Pinout

This module uses a single 12-pin 0.1" header to interface with the host board.

Pin	Name	Description
TXD	Transmit Data	Single-ended input to differential transmitter
RXD	Receive Data	Single-ended output of differential receiver
LOS	Loss of Signal	Active high output indicating optical power level is below receiver threshold.
FLT	Transmitter Fault	Active high output indicating low optical output at the transmitter. Toggling DIS will reset the transmitter to recover from the fault condition.
DIS	Transmitter Disable	Enable the transmitter by pulling this pin LOW. If left floating or HIGH the transmitter will be disabled.
DET	Module Detect	Pulled low by the SFP module after successful startup
SDA	Serial Data	Data line of two-wire diagnostic and monitoring (MOD_DEF) interface
SCL	Serial Clock	Clock line of two-wire diagnostic and monitoring (MOD_DEF) interface
VCC	Supply	Power supply from host board (3.3V DC)
GND	Ground	Common ground with host board. The SFP cage is also connected to ground.

Schematic

Manufacturer / Model	Nominal Data Rate	Wavelength	Lowest Stable Rate (50% duty cycle)
Cisco GLC-SX-MM	1.25 Gbps (1000BASE-SX 1GbE)	850 nm	50 kHz
Finisar FTLF8524P2BNL	1.062, 1.25, 2.125, 4.25 Gbps	850 nm	50 kHz
Cisco Compatible GLC-FE-100FX	125 Mbps (100BASE-FX 100MbE)	850 nm	N/A

Further Reading

SFP Design Guide
SFP Diagnostic Monitoring Interface Specification

TOSLINK Pmod

TOSLINK is a connector standard which is used to carry S/PDIF digital audio over an optical fibre. Transmitters are cheap as they use an LED instead of a laser to emit light into the fibre. This pair of Pmods use the Cliff OTJ-5 (RS 805-1680) and ORJ-5 (RS 805-1671) transmitter and receiver which are capable of up to 16 Mbps.

Downloads

Schematic

Raspberry Pi Pico Pmod Adaptor

The Raspberry Pi Pico is a development board based on the RP2040 microcontroller. This PCB design adds a Pmod compatible host connector to the Raspberry Pi Pico. The 3.3v regulator on the Raspberry Pi Pico can supply about 300mA which is sufficient for the 100mA limit specified in the Pmod Standard.

Downloads

Schematic

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