I have a device which can act as a Modbus master and can be set-up to poll or write a set of addresses on a modbus slave. As far as I can tell it doesn't accept unsolicited writes from the Modbus slave. If I understand correctly, when you connect a touch panel, the panel attempts to write plc addresses when a user interacts with the panel. The only way I've been able to get it to work is to place a PLC between the panel and our "Device" and poll the PLC addresses which the panel is allowed to write. Is there a cleaner solution such as some kind of bridge that will emulate a PLC and allow the touch panel to write addresses while out "Device" polls the addresses in the bridge?

 

Both of the devices you have are functioning as Modbus Masters. The rules of Modbus say that there can only be one Master on a network. So, you need a device that will allow both Masters to exchange data and that is what you have done with the PLC. It is a Modbus Slave to both Masters.

You could also use the MARC Omnii-Comm http://www.miille.com/din266-p00.pdf module to do this. You can simply configure the module to have blocks of Modbus registers or coils that can be accessed from either Master. It can support over 700 Holding Registers and up to 4096 Coils.

Contact me directly at jmiille at miille dot com if you have any further questions.

Thanks,

Jerry Miille