I/O extension uses two concepts: nets and devices. An I/O extension network consists of a master and up to 64 slave devices connected to the net by using the RS-485 physical media. Connection between the master and the devices is called a "net". The master device updates the in- and outputs by reading/writing to the registers of the slave devices. Each slave device has a unique ID and only accepts commands that are sent to it.
This architecture is illustrated below:
Nets
A net is a connection to the RTCU device where one or more devices can be connected.
There are two different modes in which a net can be used: master and slave.
Devices
A device is a remote device that offers inputs and/or outputs. Only a master device can trigger a communication with a device.
Modes
The RTCU device can act as master or slave on the MODBUS network.
- Master: In master mode, the RTCU device uses the connected devices to extend the number of in- and outputs.
When it is configured as master, it controls the communication with the devices.
- Slave : In slave mode, the RTCU device offers its in- and outputs to a remote master device.