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Digilent Pmod™ Interface Specification 1.2.0

Revised October 5, 2017

Other product and company names mentioned may be trademarks of their respective owners.

Page 1 of 11

1 Introduction

The Digilent Pmod interface is used to connect low frequency, low I/O pin count peripheral modules to host

controller boards. There are six-pin and twelve-pin versions of the interface defined, encompassing SPI, I²C, UART,

S, H-bridge and GPIO protocols. The six-pin version provides four digital I/O signal pins, one power pin and one

ground pin. The twelve-pin version provides eight I/O signal pins, two power pins and two ground pins. The signals

of the twelve-pin version are arranged so that it provides two of the six-pin interfaces stacked.

In general, Pmod modules can plug directly into connectors on the host controller board, called host ports, or be

connected to the controller board via six-pin or twelve-pin cables. Two six-pin peripheral modules can be

connected to a single twelve-pin host port via a twelve-pin to dual six-pin splitter cable. Similarly, a single twelve-

pin peripheral module can be connected to two six-pin host ports via the same twelve-pin to dual six-pin splitter

cable.

Pmod modules are powered by the host via the interface’s power and ground pins.

The Pmod interface is not intended for high frequency operation, however, using RJ45 connectors and twisted pair

Ethernet cable, signals have been sent reliably at 24 MHz and distances of up to 4 meters. Theoretically, signal

speeds greater than 100 MHz should be achievable using high-speed ports with direct connection of Pmod

modules (without the use of cables).

2 Electrical Specifications

The digital signal characteristics are not specified. However, the general expectation is that a 3.3 V logic power

supply will be used and the signals will conform to LVCMOS 3.3 V or LVTTL 3.3 V logic conventions.

The driver current source/sink capability isn’t specified and depends on the capabilities of the specific system

board or module. The I/O pins on the system board are generally directly driven by the FPGA or microcontroller.

The drive strength for FPGA pins is generally in the range +/-16 mA to +/-24 mA. The drive capability of

microcontrollers is generally less and some of them are not symmetrical. The drive strength for microcontroller

pins is generally in the range +/-5 mA to +/-10 mA.

The I/O pins on standard system board Pmod ports generally have ESD protection diodes and 200-ohm series

resistors. The resistors are to limit short circuit currents if pins are inadvertently shorted, or to protect against

driver conflicts if outputs are inadvertently connected together. High-speed Pmod ports are present on some

Digilent system boards and do not have ESD protection diodes or series resistors.

Summary of content (11 pages)

PAGE 1
300 Henley Court Pullman, WA 99163 509.334.6306 www.store. digilent.com Digilent Pmod™ Interface Specification 1.2.0 Revised October 5, 2017 1 Introduction The Digilent Pmod interface is used to connect low frequency, low I/O pin count peripheral modules to host controller boards. There are six-pin and twelve-pin versions of the interface defined, encompassing SPI, I²C, UART, I2S, H-bridge and GPIO protocols. The six-pin version provides four digital I/O signal pins, one power pin and one ground pin.
PAGE 2
Digilent Pmod™ Interface Specification 1.2.0 Peripheral modules may be connected to the host via cables of up to 18” in length. The drivers on the host or peripheral module should have sufficient drive strength to drive this length of cable at whatever the operating speed of the interface on the Pmod is expected to be. In general, this means that the driver should be able to source or sink at least 5 mA of current.
PAGE 3
Digilent Pmod™ Interface Specification 1.2.0 The host board will typically have a 12-pin right angle female connector at the board edge for direct connection of peripheral module boards, however a straight female connector inboard from the board edge is also allowed. When multiple Pmod host ports are placed side-by-side along a host board edge, they are spaced 0.9” center-tocenter. This allows for 0.8” wide modules to be plugged side-by-side into a host without mechanical interference.
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Digilent Pmod™ Interface Specification 1.2.0 Figure 2. Standard 12-pin male connector placement on Pmod boards. Figure 3. Standard 6-pin female connector placement on Pmod boards. Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.
PAGE 5
Digilent Pmod™ Interface Specification 1.2.0 Figure 4. Standard 12-pin female connector placement on Pmod boards. Figure 5. Standard 12-pin female host port placement on host boards. Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.
PAGE 6
Digilent Pmod™ Interface Specification 1.2.0 The connection standard for system boards that provide I²C connectors is to use the standard 12-pin right angle female connector at the board edge for direct connection of peripheral module boards. The connector provides two sets of the I2C signals, power and ground, so that the I2C bus can be formed by daisy chaining system boards or Pmods. The system board can either be the root of one or two daisy chains, or in the middle of a daisy chain.
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Digilent Pmod™ Interface Specification 1.2.0 5.2 SPI Pmod Interface Type 2 (SPI) This provides a Serial Peripheral Interface (SPI) port. The host generally acts as an SPI master device and the peripheral module generally acts as an SPI slave device. When this interface is placed on a 12-pin connector on a host, it should use pins 1-6 (i.e. the upper row of pins). Pins 1-6 will adhere to the signals listed in the table, with the exception of one or more pins potentially being unconnected.
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Digilent Pmod™ Interface Specification 1.2.0 RESET CS2 CS3 5.3 - Reset signal for master to reset slave - Chip Select 2. Active low to enable second slave device - Chip Select 3. Active low to enable third slave device UART Pmod Interface Type 3 (UART) This provides a UART interface with optional hardware flow control. When this interface is placed on a twelve-pin connector on a host, pins 1-6 should be used (i.e. the upper row of pins).
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Digilent Pmod™ Interface Specification 1.2.0 Pin # Signal Direction Alternate Signal Direction 1 2 3 4 5 6 7 8 9 10 11 12 CTS TXD RXD RTS GND VCC GPIO GPIO GPIO GPIO GND VCC In Out In Out GPIO GPIO In/Out In In/Out In/Out In/Out In/Out INT RESET - In Out - CTS RTS RXD TXD INT RESET 5.
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Digilent Pmod™ Interface Specification 1.2.0 Pin # Signal Direction 1 2 3 4 5 6 DIR1 EN1 DIR2 EN2 GND VCC Out Out Out Out DIR1 EN1 DIR2 EN2 - Motor/Phase 1 direction - Motor/Phase 1 enable, active high - Motor/Phase 2 direction - Motor/Phase 2 enable, active high Pmod Interface Type 5A (Expanded Dual H-Bridge) This interface provides for controlling two independent H-Bridges with motor speed sensing feedback. The DIR pin sets the rotational direction of the motor.
PAGE 11
Digilent Pmod™ Interface Specification 1.2.0 5.5 I²C Pmod Interface Type 6 (I²C) This interface conforms to the I2C specification, plus an optional interrupt and reset pin. If these optional pins are not used, they will be no connects. The pull-up resistors used to provide the logic high level for SCL and SDA are provided on the modules and can be attached to or detached from the bus via onboard jumpers.