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RS485/RS422 transmission module, galvanic isolation, UEXT

OLI-MOD-RS485-ISO

Adapter RS232/I2C to RS485

  • Power: 3.3V
  • Half duplex / Full duplex
  • Data interface: UART or I2C
  • Configure interface: I2C
  • 1 000 000 bauds
  • UEXT interface
  • MOD-RS485-ISO - PIC16F18324

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Description

Transmit in full duplex to RS485 from Serial line or I2C line

Note: this is the last revision of the module propelled with PIC16F18324

MOD-RS485-ISO uses an ISO35T from Texas Instruments and offers a 3000V galvano isolation RS485/RS422 interface.

This module can be used to convert RS232 or I2C to a full duplex RS485/RS422. The board is fitted with an UEXT connector and can be wired with Dupond or plugged on an UEXT capable board.

This module is an excellent choice for conveying information over long distances (1200m) allowing an error-free data transmission.

This device if fitted with a PIC16 MCU taking care of the full duplex communication (open-source firmware).
The PIC16 handle on of the both mode:

  • Pass mode: the UART (RX/TX) is used to communicates over the RS485 lines.
  • Bridge mode: the I2C bus is used to communicates over the RS485 lines (UART lines are disabled)

The PIC16 also brings up the I2C bus (SDA/SCL) to manage the RS485 board parameters and status. The I2C bus can also be used in Bridged mode.

The PIC16 firmware support the following baudrates: 134, 150, 300, 600, 1200, 1800, 2400, 4800, 7200, 9600, 14400, 19200, 38400, 57600, 76800, 115200, 128000, 230400, 500000, 576000, 1000000.

The board is also shipped with Arduino based examples :

  • ChangeAddress : change the I2C address of the module on the I2C bus
  • CheckDevice : just read the parameter of the device, mode, RS485 direction status (emit/receive), Baud rates.
  • Receive : how to read the RS485 bus in bridge mode (over the I2C bus) and forward it back on the Arduino's serial monitor
  • Sender : send the bytes received from the Arduino's serial monitor to the RS485 configured in bridge mode (so over the I2C bus)
  • BidgeMode : set the board in full-duplex (RX/TX enabled at the same time) to send data then read the response.

More information on the manufacturer product page.

Technical details

  • ISO35T converter from Texas Instruments
  • PIC16F18324 (previous hardware revisions used PIC16F1503)
  • Custom firmware loaded on the PIC16, allowing easier interfacing
  • ICSP connector for programming with PIC16-compatible programmer
  • LEDs on ICSPDAT and ICSPCLK lines
  • UEXT connector (or can be wired with Dupont wires).
  • RS485 connector full duplex
  • RS485/RS422 compatible
  • Dimensions: (58 x 30)mm
  • Schematic, user manual, firmware (Olimex)

FAQ

I found a very nice example of MOD-RS485 connected to another board in the internet. It doesn't work despite that I use the same setup as the author. What might be different?

There are number of firmware revisions that had been released for MOD-RS485. You should ensure the example you have found used the same firmware revision of MOD-RS485 as the one you have on the module at the moment. Each firmware uses a different board address (0x22 for newer firmware vs 0x48 for firmware 1, for instance) AND DIFFERENT PROTOCOL. Each firmware has a README file inside the source archive that is available for download. Refer to that README for more information about the firmware and its usage.

I have MOD-RS485-ISO with PIC16F1503 and I can't load the latest firmware release. Why?

Only MOD-RS485-ISO boards equipped with PIC16F18324 are compatible with the latest firmware released. The last firmware release for MOD-RS485-ISO boards with PIC16F1503 is release #4. Make sure to use that one.

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