Command String

Hi, I'm trying to interface credit cards to my self serve car wash and I'm workng with a programmer for the web. Here is where I'm having trouble, the programmer need to now the command string to turn "ON" a PLC, and he is not familar with MODBUS protocol.

I'll be communicating over MODBUS TCP/IP...So validating the credit card from the car wash to the web my programmer can do. All he needs to know is after the credit card is validated how to send the command to the PLC to turn on. Is there anybody who can provide me with some assistance as to the command string that would be required to accomplish this.

Thanks
Tom

I think you mean you want to internally hit the "Cycle Start" in the PLC. You'll need to know how that works in the PLC which means you'll need access to the program. The mfg of the equipment should have it and then you'll may need the help of a local programmer to make any changes. It could be as simple as mirroring the "Cycle Start" input PB if it exists.

The public domain implementation of Modbus does not include any instructions to start or stop the execution of a PLC program. It does allow you to write an ON or OFF state to a bit or a numeric value to a data register. You may have to modify the ladder logic that controls the sequence of operations to include a command from the credit card validation device.