ПЛК73 и RS-485

[Денис_Гуливатенко]

Нашел интересный ответ на глобальном сайте производителя преобразователя:

Be careful. If you want write the parameter, these address are different.
Modbus address=Inv address – 1
If you want write Frequency to Inverter(0x0005), you must use 0x0004 (modbus)
And, you want write operation command to INV (address : 0x0006), you must use 0x0005 (Modbus).
Moreover, operation command has bit segments.
So, you use MOVE function.
For example, [MOV 1 m0] means PLC make INV being forward running status.
[MOV 16 m0] means PLC make INV being emergency stop status.

IG5A address for Modbus RTU should be IG5A address minus 1.
So if you want to write frequency command address 5, you have to set 0x40004.
And you have to set 0x40005 for RUN command like forward RUN, reverse RUN and STOP command.

Почему "address 5" minus "1" = "0x40004", объясните пожалуйста?