Information

Digilent Pmod™ Interface Specification

www.digilentinc.com page 8 of 11

Pin Signal Direction

1 CTS Out

2 RTS In

3 RXD In

4 TXD Out

5 GND

6 VCC

CTS - Permission for peripheral to send data to host

RTS - Request from peripheral to send data to host

RXD - Data from peripheral to host

TXD - Data from host to peripheral

Pmod Interface Type 4 (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). The

hardware flow control signals are optional, and some Pmods do not use them. In this case pins 1

& 4 are not used.

The hardware flow control signal names are defined from the system board perspective. The RTS

signal is an output indicating that the device (host or peripheral) is ready to receive data. The

device asserts this signal low when it is ready to receive data. The CTS signal is an input to the

device (host or peripheral). The device will only transmit data when the CTS input is asserted low.

A peripheral module that uses hardware flow control will connect the host’s RTS signal to its

internal CTS input and the host’s CTS signal to its internal RTS output.

NOTE: This interface type supersedes the Type 3 UART interface. System and peripheral module

boards designed after 07/2010 use this signal definition for UART connectors. When making

connections between the Type 3 UART interface and the Type 4 UART interface, a flying lead

cable or crossover cable is required.

The change in UART signal definition from Type 3 UART to Type 4 UART was motivated by the

fact that some microcontroller families (notable some Microchip PIC32 parts) have serial interface

controllers that support both SPI operation and UART operation. This signal definition allows

system boards using those microcontroller chips to have Pmod connectors that can support both

SPI and UART on the same connector.