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1300 Henley Court Pullman, WA 99163 509.334.6306 www.digilentinc.com PmodRS485™ Reference Manual Revised April 12, 2016 This manual applies to the PmodRS485 rev. B Overview The Digilent PmodRS485 provides signal and power isolation for high speed communication lines utilizing the RS485 communication protocol. 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 The PmodRS485. 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 Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners. Page 1 of 4 PmodRS485™ Reference Manual Inputs A-B Voltage Difference ≥ -0.03V ≤ -0.2V -0.2V < A-B < -0.03V Inputs Open Don't Care Output ~RE RxD Low or Not Connected Low or Not Connected Low or Not Connected Low or Not Connected High High Low Don't Care High High Impedance Table 1. Receiving. Inputs DE High High Low Output TxD Y High Low Don't Care Z High Low High Impedance Low High High Impedance Table 2. Transmitting. Pin 1 2 3 4 5 Signal ~RE TxD RxD DE GND Description Receive Enable Transmit Data Receive Data Driver Enable Power Supply Ground 6 VCC Positive Power Supply (3.3V/5V) Signal A B Z Y Table 3. Pinout description table: Pmod Header J2. Description Input A Input B Output Z Output Z Table 4. Screw terminals. RE B-input TXD JP1 A-input RXD DE RS485 Transceiver Y-output GND Z-output VCC Figure 1. PmodRS485 functional block diagram. Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners. Page 2 of 4 PmodRS485™ Reference Manual 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. JP1 RS485 A Y B Z Z B Y A JP1 B A Y Z A Z B Y JP1 RS485 RS485 JP1 RS485 RS485 RS485 Shorted jumper Not Shorted Jumper Figure 2. Half-duplex communication. JP1 RS485 A Y B Z Z B Y A JP1 A B Z Y A B Z Y JP1 RS485 RS485 JP1 RS485 RS485 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. Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners. Page 3 of 4 PmodRS485™ Reference Manual 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. Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners. Page 4 of 4