Digilent Pmodrs485 High-speed Isolated Communication User Manual (+ PDF)

The PmodRS485 utilizes Analog Devices ADM2582E to facilitate
RS-485 and RS-422 serial communication protocols between devices in
environments with high electrical noise. The ADM2852E provides both
signal and power isolation allowing for accurate data transfer
across long distances. Data transmission rates of 16 Mbit/s can be
achieved.

Interfacing with the Pmod

The PmodRS485 communicates with the host board via the UART
protocol. In order to transmit data, the Driver Enable line (DE)
must be pulled to a logic level high voltage state; similarly, in
order to receive data, the Receive Enable line (~RE) must be driven
to a logic level low voltage state.

Pinout description table: Pmod Header J2

Pin	Signal	Description
1	~RE	Receive Enable
2	TxD	Transmit Data
3	RxD	Receive Data
4	DE	Driver Enable
5	GND	Power Supply Ground
6	VCC	Positive Power Supply (3.3V/5V)

Screw terminals

Signal	A	B	Z	Y
Description	Input A	Input B	Output Z	Output Y

Chaining Multiple PmodRS485 Devices

Multiple PmodRS485 devices can be chained together up to 256
nodes in total. When two PmodRS485s are connected, JP1 should be
loaded on both devices. When more than two PmodRS485s are
connected, JP1 should only be loaded on the two devices at the
terminating ends of the wire, and stubs off of the main line should
be kept as short as possible.

Half-duplex communication

Full-duplex communication

Power Supply

Any external power applied to the PmodRS485 must be within 3.0V
and 5.5V; however, it is recommended that Pmod is operated at
3.3V.

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PmodRS485TM Reference Manual
Revised February 9, 2021 This manual applies to the PmodRS485 rev. B

1300 Henley Court Pullman, WA 99163
509.334.6306 www.digilentinc.com

Overview
The Digilent PmodRS485 provides signal and power isolation for high speed communication lines utilizing the RS485 communication protocol.

The PmodRS485.

Features include:
· High-speed RS-485 communication module · Isolated RS-485/RS-422 interfaces for use in
noisy environments · 16Mbps maximum data rate · Connect up to 256 nodes on one bus · Differential half or full-duplex
communication · Thermal shutdown and ±15kV ESD
protection · 6-pin Pmod port with UART interface · Library and example code available
in resource center

1 Functional Description
The PmodRS485 utilizes Analog Devices ADM2582E to facilitate RS-485 and RS-422 serial communication protocols between devices in environments with high electrical noise. The ADM2852E provides both signal and power isolation allowing for accurate data transfer across long distances. Data transmission rates of 16 Mbit/s can be achieved.

2 Interfacing with the Pmod

The PmodRS485 communicates with the host board via the UART protocol. In order to transmit data, the Driver Enable line must be pulled to a logic level high voltage state; similarly, in order to receive data, the Receive Enable line must be driven to a logic level low voltage state.
Truth tables indicating the status of the various pins of the PmodRS485 are provided below:

DOC#: 502-310
Downloaded from Arrow.com.

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PmodRS485TM Reference Manual

A-B Voltage Difference -0.03V -0.2V -0.2V < A-B < -0.03V Inputs Open Don’t Care

Inputs
~RE
Low or Not Connected Low or Not Connected Low or Not Connected Low or Not Connected High

Output
RxD
High Low Don’t Care High High Impedance

Table 1. Receiving.

DE High High Low

Inputs TxD
High Low Don’t Care

Output

High

Low

High

High Impedance High Impedance

Table 2. Transmitting.

Signal Description

~RE

Receive Enable

TxD

Transmit Data

RxD

Receive Data

Driver Enable

GND Power Supply Ground

VCC

Positive Power Supply (3.3V/5V)

Table 3. Pinout description table: Pmod Header J2.

Signal A B Z Y

Description Input A Input B Output Z Output Z

Table 4. Screw terminals.

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PmodRS485TM Reference Manual

Figure 1. PmodRS485 functional block diagram.
Multiple PmodRS485 devices can be chained together up to 256 nodes in total. When two PmodRS485s are connected, JP1 should be loaded on both devices. When more than two PmodRS485s are connected, JP1 should only be loaded on the two devices at the terminating ends of the wire, and stubs off of the main line should be kept as short as possible.

RS485

A JP1
B
Z
Y

ABZ Y JP1
RS485

ABZY JP1
RS485

RS485 RS485

Figure 2. Half-duplex communication.

Y Z B A JP1

RS485

Shorted jumper Not Shorted Jumper

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PmodRS485TM Reference Manual

RS485

A JP1
B
Z
Y

ABZ Y JP1
RS485

RS485 RS485

ABZY JP1
RS485

Y Z B A JP1

RS485

Shorted jumper Not Shorted Jumper

Figure 3. Full-duplex communication.
Any external power applied to the PmodRS485 must be within 3.0V and 5.5V; however, it is recommended that Pmod is operated at 3.3V.
3 Physical Dimensions
The pins on the pin header are spaced 100 mil apart. The PCB is 1.5 inches long on the sides parallel to the pins on the pin header and 0.8 inches long on the sides perpendicular to the pin header.

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