DAISY-10 - RS485/422 optoisolated interface

RS485/RS422 opto-isolated interface

The Daisy-10 is a RS485 half-duplex interface or RS422 full-duplex interface for Terra and Fox boards. It can be configurate ad opto-isolated or not via a set of dip switches. When configured in RS485 mode up to 32 devices are pluggable on a single RS485 bus line.

The board is built around a Texas Instruments ISO35 that provide 2500 Vrms of isolation with the on-field bus line. When isolated an external 3.3VDC power lines is required.

The daisy connectors where it's possible to plug this board are:

TERRA FOX G20 Serial device Mode available
D13 D1 /dev/ttyS2 RS422 or RS485
D3 /dev/ttyS1 RS422 or RS485
D10 D6 /dev/ttyS4 RS422 or RS485
D8 /dev/ttyS3 RS422

On the FOX Board G20 is requested a Daisy-1 adapter to wire-up this boards.

Errata corrige

We found a hardware bug when this board is used in isolated mode. Please verify whether the D1 led (3V3) is already removed, if not please remove it. If you are using the board in not isolated mode you can leave it.

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 standard is widely used for communications in industrial automation because it can be used effectively over long distances and in electrically noisy environments.

Even though the data is 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.

RS485 dip-switch setup

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

The picture below illustrates a typical RS485 wiring in non isolated mode. In isolated mode you have to provide the 3.3VDC. Don't forget to place a 120 resistor on the last node.

Code example

Following an example of code in Python to use the Daisy-10 module in RS485 mode.

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

rs485example.py

RS422 mode

The picture below illustrates a typical RS422 wiring in non isolated mode. In isolated mode you have to provide the 3.3VDC.

RS422 dip-switch setup

Dip-switch # --> 1 2 3 4 5 6 7 8
RS422 mode OFF OFF OFF OFF OFF OFF
Isolated OFF OFF
Not isolated ON ON

Code example

Following an example of code in Python to use the Daisy-10 module in RS422 mode.

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

rs422example.py

Terminal block pinout

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

Pin Signal
GND GND signal when not isolated or external GND line when isolated
Y (TX+) RS422 TX+ line
Z (TX-) RS422 TX- line
B (RX-) RS422 RX+ line or RS485 B line
A (RX+) RS422 RX+ line or RS485 A line
3V3 3V3 volt output when not isolated or external 3.3 VDC line when isolated

Dip-switch set up

Ten dip-switches are available to configure your Daisy-10 interface in RS485 or RS232 mode. This is a list of each dip function. Quick configuration tables are available later in this article.

Dip-switch # Function
1 When ON wires the internal 3.3V to the screw driver terminal. Let it OFF for isolated interfacing
2 When ON wires A to Y
3 When ON wires B to Z
4 When ON wires a 120 resistor between the A and B terminal
5 When ON wires the internal GND to the screw driver terminal. Let it OFF for isolated interfacing
6 When ON wires the CPU RTS signal to the DE IC driver
7 When ON wires DE to RE# on IC driver
8 When ON wires the CPU CTS signal to the RE# IC driver

Schematics, datasheets and related links

DAISY-10
EUR 22.00


Daisy isolated RS485/422 module

DAISY-10 is an isolated RS485/RS422 interface.

Note: the daisy flat cable to wire this board is not included. Don't forget to buy it (code FLAT-20CM)

| Product description | Daisy catalog |

FLAT-20CM
EUR 2.00


Flat cable 10 wires, 20 cm, pitch 1.27 mm

Ribbon cable for YARM-DEV or DAISY modules wiring:

  • Length 20 cm
  • 10 wires
  • Pitch 1.27 mm

TERRA
EUR 169.00


Linux embedded board for fast prototyping

TERRA is a carrier board conceived both to evaluate the Aria G25 SoM and to make prototypes or small production batches of OEM equipments using the Daisy cabling system.

| Product description | Terra catalog |