RS485 Pi
Features
RS‐485 Half Duplex Port.
Up to 250 kbps transfer rate.
Use the Raspberry Pi to control external RS‐485 devices.
Stackable with other Raspberry Pi accessory boards.
Mounting holes for use with the AB Electronics UK mounting kits (sold separately)
The RS485 Pi is a communication board supporting the RS‐485 serial protocol.
The RS‐485 port is connected to the UART port on the Raspberry Pi using a
SN65HVD72 interface. The SN65HVD72 IC converts the 3.3V UART signals to RS‐
485 voltages allowing communication with RS‐485 compatible devices over a DB9
serial cable or twisted pair cable. The RS‐485 port can be accessed through the DB9
port or the solder points on the PCB.
The RS485 Pi contains protection against voltage spikes in the form of a TVS Diode
and two 10‐Ω, Pulse‐Proof Thick‐Film Resistors.
Please note that you can only use one RS485 Pi board on a Raspberry Pi. if stacking
with other boards we recommend putting the RS485 Pi at the top of the stack due to
the height of the DB9 connector.
Using RS‐485*You need to use the latest Raspbian Jessie release and disable the
built in Bluetooth to use the RS485 Pi on the Raspberry Pi 3, see our KB page for the
config changes needed.
RS‐485, also known as ANSI/TIA/EIA‐485, TIA/EIA‐485 or EIA‐485 is a standard
used in serial communication systems. Equipment using the RS‐485 standard can be
used over long distances in noisy environments. Unlike
RS232, the RS‐485 standard allows for multiple devices to be connected on the same
network. The recommended arrangement for connecting devices to an RS‐485
network is to use a series on nodes connected along a line or bus with terminating
resistors used at either end of the bus to reduce reflections.
A 120‐Ω resistor is included with the RS485 Pi which will need to be fitted if the
board is connected to the end of the RS‐485 bus. The diagram below shows a typical
network of RS‐485 devices.
Input Ratings & Specifications
Supply Voltage: 3.3V
Logic Voltage at GPIO Port: 3.3V
Differential Input Voltage at A & B: ‐12V to +12V
input voltage: 2V
Low‐level input voltage: 0.4V
Signalling Data Rate: 250 kbps
Assembly
The RS485 Pi is supplied with the 40 pin GPIO connector and the DB9 connector
unsoldered.
A 120R terminator resistor is included in the kit. This will be required if the RS485
Pi is used as an end node within an RS485 network.
Before using the RS485 Pi you will need to solder both connectors onto the PCB. We
suggest soldering the 40 pin GPIO connector first and then the DB9 connector.
Connecting to the RS‐485 Port
The RS‐485 port on the RS485 Pi can be accessed through the male DB9 socket or
the solder points on the PCB. The DB9 socket uses three wires as shown on the
diagram below.
https://uk.pi‐supply.com/products/rs485‐pi/3‐20‐19
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