ICP DAS USA GW-7553-B User Manual page 22

Figure 18 GW-7553-B / GW-7553-M output data to Modbus Slave devices
Figure 19 GW-7553-B / GW-7553-M receive data from Modbus Slave devices
When the GW-7553-B / GW-7553-M acts as a Modbus Slave device, it can
receive query message from Modbus Master device and then saving to internal
DO、AO memory space. It can also send response message to Modbus Master
device through internal DI、AI data, as shown in Figure 20
GW-7553-B / GW-7553-M PROFIBUS/Modbus TCP Gateway User Manual (Version 1.35, May/2017)
PAGE: 22
、
Figure 21.