Topologies

Figure 1-2 shows the relationship between multiple products (slaves) and a Modbus master (assuming RS-485).

Figure 1-2 - Relationship between Modbus Master and Slaves on RS-485 Network.

Figure 1-3 shows the relationship between multiple products (slaves) and multiple Modbus masters (assuming RS-485 in the example) with one of those products being µC/Modbus-M. You will note that only one master can be present on each RS-485 network.

Figure 1-3 - Multiple Modbus Masters and Slaves on RS-485 Networks.

Figure 1-4 shows the relationship between multiple products (slaves) and multiple Modbus masters (assuming RS-232C in the example). As you can see, with RS-232C, each master needs to have a direct connection to each slave. µC/Modbus supports this topology since each product can have multiple communication channels. Although RS?232C requires more point-to-point connections, it offers the benefit of higher throughput since communications can occur concurrently instead of sequentially.

Figure 1-4 - Multiple Modbus Masters and Slaves with RS-232C.

Modbus allows you to read or write integer, floating-point (assuming the Daniels Extensions) and discrete values from/to your target system. µC/Modbus can read or write from/to:

up to 65536 16-bit integer values,

up to 65536 32-bit floating-point values,

up to 65536 coils, and

up to 65536 discrete inputs.

Integer and floating-point requests may not be mixed in the same command. Multiple integer values (up to 125) and multiple floating-point values (up to 62) may be written via a single command.

Depending on the processor you are using, you should be able to run µC/Modbus with data rates from 9600 up to 256,000 baud. The baud rate you can attain is actually limited to the performance of the CPU and not µC/Modbus.