Daisy System RS485/RS422 Interface Module, Opto-Is

Daisy System RS485/RS422 Interface Module, Opto-Isolation Option	US$20.00
DAISY-10

Daisy System RS485/RS422 Interface Module, Opto-Isolation Option

DAISY-10 is an RS485 half-duplex or RS422 full-duplex interface module with selectable opto-isolation and configuration via DIP switches. When configured in RS485 mode, up to 32 devies are pluggable on a single bus line.

This board is part of the modular Daisy System that can be controlled by the FOX Board G20 via the DAISY-1 Adapter, or by the Terra Board.

The board uses a Texas Instruments ISO35 transceiver which provides 2500 Vrms of isolation with the on-field bus line.

Refer to the following table to determine which DAISY-1 (Fox) or Terra port you might want to use.

Port Serial device Signals

Fox D1 /dev/ttyS2 RS422 or RS485

Fox D3 /dev/ttyS1 RS422 or RS485

Fox D6 /dev/ttyS4 RS422 or RS485

Fox D8 /dev/ttyS3 RS422

Terra D10 /dev/ttyS4 RS422 or RS485

Terra D13 /dev/ttyS2 RS422 or RS485

Be sure to get a 0.05" pitch 2x5 IDC cable (FC-19818-10P-FF) to make the connection. The cable is not included.

Terminal Block Pinout

The bus line signals are available on a terminal block with 3.81mm pitch.

Pin Signal

GND GND signal when not isolated; external GND line when isolated
Y RS422 TX+ line
Z RS422 TX- line
B RS422 RX- line or RS485 B line
A RS422 RX+ line or RS485 A line
3V3 3V3 volt output when not isolated; external 3.3V DC line when isolated

DIP Switch Settings

Eight DIP switches allow you to configure your DAISY-10 module. To turn off isolation, you would set switches 1 and 5 to ON. Note: If you want to use isolated mode, you should remove LED D1 (3V3) from the board, due to a design flaw.

Switch Function when ON

1 Wires internal 3.3V to screw terminal
2 Wires A to Y
3 Wires B to Z
4 Wires a 120Ω resistor between A and B
5 Wires internal GND to the screw terminal
6 Wires CPU RTS signal to DE IC driver
7 Wires DE to RE# on IC driver
8 Wires CPU CTS signal to RE# IC driver

Using DAISY-10 in RS485 mode

RS485, also known as TIA/EIA-485, is a standard defining the electrical characteristics of drivers and receivers for use in balanced digital multipoint systems. This communications standard is common in industrial automation because it can be used effectively over long distances and in electrically noisy environments.

Even though the data are transmitted over a 2-wire twisted pair bus, all RS485 transceivers interpret the voltage levels of the differential signals with respect to a third common voltage. Without this common reference, a set of transceivers may interpret the differential signals incorrectly.

The image below illustrates typical RS485 wiring in non-isolated mode (i.e., DIP switches 1 and 5 ON). For isolated mode, you will have to provide the 3.3V DC (and remove LED D1 from the board). Remember that the last node on the bus must have a 120Ω resistor for termination.

DIP Switch → 1 2 3 4 5 6 7 8

RS485 mode ON ON ON OFF

Isolated OFF OFF

Not isolated ON ON

A & B terminated ON

A & B not terminated OFF

RX disabled on TX ON

RX always enabled OFF

Using DAISY-10 in RS422 mode

In RS422 mode, set all DIP switches to OFF, except maybe 1 & 5 to turn off isolation. The image below illustrates typical RS422 wiring in non-isolated mode (i.e., DIP switches 1 and 5 ON). For isolated mode, you will have to provide the 3.3V DC (and remove LED D1 from the board).

RS485/RS422 Module Examples

These Python code examples run on the Terra Board with this module plugged into D10. You can modify the source code easily to run it on the Fox Board, e.g. change the port to D6.

The examples call the ablib Library.

The Daisy-10 class is a derived class from the pySerial where it is possible to call the serial ports also with the Daisy connectors name like D1, D10, etc instead of /dev/ttyS2, /dev/ttyS4 etc. Refer to the pySerial docs to learn more about its use: