There two different sets of commands that can be used for controlling digital I/O. the lowest level of control involves the user sending Modbus commands directly, using the Galil command MB. The alternative is to use the standard Galil commands for setting I/O on the controller, there are two digital output commands, and they are SB and CB command.
These commands are the common Galil commands to control I/O, but when connected on port 502, the controller then convert them to Modbus before they are sent out. With these commands there is one more catch to the addressing, the controller needs to know which handle the PLC is connected to, and that is done with the following equation:
Address= (Handling Number)*1000 + Bit number
Handle Number: this is the number that corresponds to the letter used when opening connection. For example, if a connection is opened with IHB=…, the handle number would be 2 because B is the second letter of the alphabet.
Bit Number: the bit number is determined with the rules from the section entitled “Addressing I/O”. Once the full address is determined, controlling the output is easy. The SB command turns the output on, and CB command clears the output.