Software version 5 and above of the 2604 controller supports Master Communications. The objective of the master comms is to allow the 2604 to communicate with any instrument using ModBus interface as a master device, that is, without the need for a supervisory PC. This allows the 2604 to link through digital communications with other products to create a small system solution.

There are two methods of communication
1. Broadcast Communications
2. Direct Read/Write

Broadcast Communications
The 2604 master can be connected to up to 32 slaves. The master sends a unit address of 0 followed by the address of the parameter which is to be sent. A typical example might be a multi zone oven where the setpoint of each zone is required to follow, with digital accuracy, the setpoint of a master.

Direct read/write
The 2604 master can be connected to up to eight slaves. Each slave has its own unit address. The master can send data to each slave by sending a unit address followed by the parameter address. It can also request data from a slave. This data may be displayed on the 2604 or used as part of a 2604 control strategy.