Use Gateway Mode
Operate GP-4G01 with Gateway Mode enabled.
While communication occurs between a host device connected to the HMI port and a device connected to the COM1 or PLC port, GP-4G01 itself can also communicate with device/PLC, and also communicate via Ethernet.
For details about the connection process, see the "GP-Pro EX Device/PLC Connection Manual".
Maximum Packet Size
Set up the value written to system variable #H_GW_DivideInterruptSize at startup.
Use to adjust the communication volume between the GP-4G01 and device/PLC. The larger the value, the more data is processed by GP-4G01 at a time, which may delay communication in existing systems. The smaller the value data is run with smaller blocks of data, which reduces the impact on communication of existing systems. 
A.2.2.2 Word Type - #H System Variables
Communication Priority
Set up the value written to system variable #H_GW_InterruptFrequency at startup.
This is a system variable for adjusting the communication speed with the device/PLC. Increase the value to give priority to communication between GP-4G01 and the device/PLC; decrease the value to give priority to communication between the host device connected to the HMI port and the device/PLC.