DIGILENT PmodRS485 High-Speed Isolated Communication User Manual
- June 12, 2024
- DIGILENT
Table of Contents
- DIGILENT PmodRS485 High-Speed Isolated Communication
- PmodRS485TM Reference Manual
- Product Overview
- Product Features
- Functional Description
- Interfacing with the Pmod
- Chaining Multiple PmodRS485 Devices
- Power Supply
- Overview
- Features include
- Functional Description
- Physical Dimensions
- References
- Read User Manual Online (PDF format)
- Download This Manual (PDF format)
DIGILENT PmodRS485 High-Speed Isolated Communication
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
Product Overview
The Digilent PmodRS485 provides signal and power isolation for high-speed communication lines utilizing the RS485 communication protocol.
Product Features
- Signal and power isolation
- Supports RS-485 and RS-422 serial communication protocols
- Accurate data transfer across long distances
- Data transmission rates of up to 16 Mbit/s
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.
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.
Overview
The Digilent PmodRS485 provides signal and power isolation for high speed communication lines utilizing the RS- 485 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
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.
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:
PmodRS485™ Reference Manual
| Inputs | Output |
|---|---|
| A-B Voltage Difference | ~RE |
| ≥ -0.03V | Low or Not Connected |
| ≤ -0.2V | Low or Not Connected |
| -0.2V < A-B < -0.03V | Low or Not Connected |
| Inputs Open | Low or Not Connected |
| Don’t Care | High |
Table 1. Receiving
| Inputs | Output |
|---|---|
| DE | TxD |
| High | High |
| High | Low |
| Low | Don’t Care |
Table 2. Transmitting
| 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) |
Table 3. Pinout description table: Pmod Header J2
| Signal | Description |
|---|---|
| A | Input A |
| B | Input B |
| Z | Output Z |
| Y | Output Z |
Table 4. Screw terminals
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.
Half-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.
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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1300 Henley Court
- Pullman, WA 99163
- 509.334.6306
- www.digilentinc.com