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Communication Between PC And Vending Machine Using PC's RS232 Using Virtual COM Port (USB) Cable And Vending Machine's Multi-Drop Bus Port (MDB) Port


New Member
I've disconnected the MDB cable from the first MDB port (MDB1) and connected it to MDB2 on the vending machine. I contacted our vending machine supplier Benleigh Vending and they stated that the switching of connections should be automatic but I can't seem to get a reply from MDB2 when I send a signal from my PC application which is sent from an application using RS232 (USB Virtual COM Port COM7) port to the MDB port on the vending machine. I chose the MDB2 port on the vending machine as MDB1 caused issues with the vending machine operations and the PC running Windows 10 Professional. I searched for a switch on the motherboard but couldn't find one. I'm wondering what I should do?


Active Member
Call tech support for the vending machine company is probably going to be your best chance of sucess, maybe they have some one who can team-viewer in and help you remotely.


Well-Known Member
Most Helpful Member
Double check in device manager that it is actually com7. Do you get an error message from the software?



Well-Known Member
Most Helpful Member
I think you will likely find the "MDB" connections are not RS232 (using 12V levels) but balanced line such as RS485 or RS422.

You can get USB-Serial adapters to suit those, but they are less common than basic USB COM Port type adapters.

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