2.2. Interface settings

Modsak uses two communications interfaces: one to communicate with Modbus masters (in slave mode and monitor mode), and one to communicate with a Modbus slave (in master mode and monitor mode). Use the Interface to Master page to configure the interface to the master(s), and the Interface to Slave page to configure the interface to the slave.

The first four items in the page must always be configured:

The Interface Type and Packet Type together determine the variant of the Modbus protocol that will be used. The table below lists the possible combinations:

Table 1. Modbus protocol variants

Interface type Packet type Protocol variant
Serial RTU Modbus RTU
Serial ASCII Modbus ASCII
Serial TCP Not recommended since no error checking (non-standard)
TCP Socket RTU Modbus RTU encapsulated in TCP (non-standard)
TCP Socket ASCII Modbus ASCII encapsulated in TCP (non-standard)
TCP Socket TCP Modbus TCP
UDP Socket RTU Modbus RTU encapsulated in UDP (non-standard)
UDP Socket ASCII Modbus ASCII encapsulated in UDP (non-standard)
UDP Socket TCP Modbus UDP (also known as Modbus TCP encapsulated in UDP) (non-standard)

The following items must be configured for a socket interface:

The following items must be configured for a serial interface:

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