(I)GW11XX Modbus User Manual
3onedata proprietary and confidential 68
Copyright © Shenzhen 3onedata Technology Co., Ltd.
12.2 Slave ID Mapping
The Modbus protocol specifies that all slave devices must have a unique ID number
(1 ~ 247). This ID number is used to identify the slave address in response to a
request from the master device. Modbus device ID number is set by the manufacturer.
In the Slave ID mapping, each slave device has two ID addresses that the virtual ID
address and the real ID address. The real ID exists in the slave device, and the other
device directly accesses the slave device via the real ID. The virtual ID exists in the
gateway, the only access address of the slave device at the gateway, and the other
devices indirectly access the slave device using the virtual ID through the gateway.
ID message processing flow:
The master device uses the virtual ID to access the gateway;
The gateway converts the virtual ID into a real ID to access the slave device;
The slave device uses the real ID to send back the response;
Gateway will be real ID converted into a virtual ID and then sent back to the
response.
