slave. This gateway follows this generally-accepted industry paradigm, where a point’s configured Modbus master “register” value is decremented by 1 before it is placed “on the wire”. Some vendors, however, will document their slave device’s “addressed as” values in their literature, which means that these register indices must have 1 added to them when entered into the gateway’s “Modbus master register” field.
For example, the Toshiba VF-AS1 drive’s Modbus RTU slave protocol implementation & corresponding user’s manual references all internal ASD parameters using “addressed as” values. This means that (in addition to the required conversion from Toshiba’s native hexadecimal radix to the Modbus protocol’s natural decimal radix) these parameter values must have 1 added to them when they are to be accessed via an ICC gateway executing the Modbus RTU master protocol.
e.g VF-AS1 “command 1” parameter is documented to be FA00 in the Toshiba literature. Converting this to decimal, we arrive at a value of 64000. To allow a point in the gateway’s database to correctly access the “command 1” parameter via Modbus RTU, therefore, that point’s Modbus master “register” attribute must be set to 64001 (which will result in an address value of 64000 (0xFA00) “on the wire”).
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