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Product of the Year 2012
RS485 Extension¶
Features¶
- Long distance connections (up to 1200m)
- Allows cable based interconnection between stacks
- Configurable baud rate, parity and stop bits
- Can be used in existing RS485 networks (Modbus RTU)
Description¶
The RS485 Extension can be used for long range cable based inter-stack communication. It uses the RS485 differential interface standard to achieve ranges of up to 1200m.
To establish a RS485 bus with Bricks, two RS485 Extensions and two Master Bricks are needed. Both Master Bricks can be connected to a full stack of Bricks and Bricklets, whereas one Master Brick is Battery powered and one is connected with USB. From a programming perspective the RS485 bus is completely transparent, i.e. the two stacks can be used exactly the same way as if they were both connected via USB.
It is also possible to create a bus with several RS485 Extension where only one is connected via USB (many-to-one routing).
Modbus RTU is used as the protocol on the RS485 interface. This allows to use a stack of Bricks and Bricklets with an RS485 Extension to be integrated in existing Modbus networks. It is also possible to communicate with a stack directly via Modbus from an embedded device or over a Modbus gateway.
The following combinations with other Extensions in a stack are possible:
- RS485 Master top / WIFI bottom
- RS485 Master top / Chibi Slave bottom
- RS485 Master bottom / WIFI top
- RS485 Master bottom / Chibi Slave top
- RS485 Slave top / Chibi Master bottom
- RS485 Slave bottom / Chibi Master top
Technical Specifications¶
| Property | Value |
|---|---|
| Current Consumption | 8mA |
| Maximum Distance | 1200m |
| Maximum Baud Rate | 2Mbit/s |
| Dimensions (W x D x H) | 40 x 40 x 16mm (1.57 x 1.57 x 0.63”) |
| Weight | 13g |
Resources¶
RS485 Bus Assembly¶
A RS485 bus consists of one master and multiple slaves. RS485 master is the Master Brick which has a USB connection to the PC running brickd. All the other Master Bricks with RS485 Extension must not have a USB connection (they can use a USB Power Supply). Each RS485 slave is identified with its own ID. The IDs have to be unique on the bus.
To create a RS485 bus, stack the RS485 Extension on top of a Master Brick. Connect the Master Brick via USB with your PC and start the Brick Viewer software. You should see the Master Brick view with the identified RS485 Extension (see images below). Configure the extension as slave or master (as described here).
If you have configured all extensions you can build your system. Connect Bricks and Bricklets as you like. The Master Brick of each stack has to be the lowermost Brick (except if you are using a Power Supply). The RS485 Extension can be positioned in the stack as you wish. Wire up the RS485 stacks and set the termination switch on the first and last RS485 Extension in the bus to “on”, as shown below.
You have to power up the slaves before the master, since the RS485 master searches for slaves only at startup. You should now be able to see all connected stacks in the Brick Viewer.
RS485 Configuration¶
To configure a RS485 Extension you first have to choose the baud rate, parity and stop bits.
If your bus isn’t absolutely huge you should probably choose “speed: 2000000 (2Mbit/s), parity: None, Stop bits: 1”. If you start to get timeouts and the CRC error counter is rising rapidly, you might want to lower the baud rate. If you want to use a stack with RS485 Extension in your existing Modbus network, you have to match the values with the other bus participants.
For slave configuration choose “Slave” as type and set an address for the slave (1-255).
For master configuration choose “Master” as type and input the addresses of the slaves in the RS485 bus as a comma separated list.
At the end, press “Save RS485 Configuration” to save the configuration permanently on the RS485 Extension. The Master Brick has to be restarted to apply the new configuration.
RS485 Bus Modification¶
If you want to change something in your bus, e.g. add new Bricks or Bricklets, you have to power down the stack you would like to change. Change it and repower it. If the stack was slave in the RS485 bus, you also have to reset the RS485 master (it only searches for new Bricks and Bricklets on startup). This can be achieved by a power cycle or pressing the reset button on the Master Brick.
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