Modsak Manual v3.16 - 1.4.2. Slave mode
In slave mode, Modsak acts as a Modbus slave, receiving requests from a Modbus master (or masters) and responding to those requests. You can use Modsak in slave mode as a simple Modbus simulator. In this role Modsak provides storage and retrieval of values in registers, but does not provide any logic to operate on those values.
To run Modsak in slave mode, perform the following steps:
In the General page (see General settings), set the Mode to Slave, and set the Slave ID to the slave identifier that you want Modsak to respond to. Modsak will also act on ) write requests using a zero slave identifier (i.e. broadcasts). Requests using any other slave identifier will be ignored.
Use the Interface to Master page (see Interface settings) to configure the interface to the Modbus master(s).
If you want to use coils or discrete inputs, or you want to use register addresses that are different from the addresses sent in messages, configure the address mapping using the Address Mapping page (see Address mapping).
If you want to use 32-bit or 64-bit values, configure the handling of these using the 32/64-bit Values page (see 32/64-bit Value Settings).
Define the registers that you want to be accessible (see Defining registers).
Click the button to open the interface and start listening for requests.
You may stop servicing of requests by clicking the button (this will close the interface), and restart servicing by clicking the button again.
While running in slave mode, Modsak will update its display of the register values that masters write to, and you may edit the values of the registers that masters read from.