You can create a communication link in your panel application to provide the gateway service that allows a computing device, such as a PC, to access the panel's internal memory and the controllers connected to the panel.
If the computing device is connected to the panel through a serial link, you need to use the service of Gateway Service (COM) , select PanelMaster's Serial Gateway Server as the server, and specify a serial port. The computing device will use the Modbus RTU protocol to communicate with the panel.
If the computing device is connected to the panel through an Ethernet link, you need to use the service of Gateway Service (Ethernet) and select PanelMaster's TCP/IP Gateway Server as the server. The computing device will use the Modbus TCP/IP protocol to communicate with the panel.
The most important thing is to specify the internal and external memory locations to be accessed at runtime in the address mapping table while configuring the link. In the address mapping table you will specify the addresses and ranges of the locations to be accessed as well as their corresponding locations in the Modbus address space.

The blue dashed lines shown in the above figure indicates that the PC can access Controller #1 through Controller #N via the panel with the help of the gateway server.
Source.Section 3.4.8 of the PM Designer Software User Manual, Edition 2.0, © Cermate Technologies Inc. (www.cermate.com, service@cermate.com). Reproduced online, with the manual's own figures, by TSL Automation Solutions, authorised Cermate distributor, for users of Cermate HMI panels. PM Designer and PanelMaster are trademarks of Cermate Technologies Inc.
Text and figures are the manufacturer's and may describe features your panel or software version does not have. For a plain-language introduction read the PM Designer guide; for help with a specific panel contact TSL Automation.