Multiplexing/Demultiplexing data over ControlNet


Thread Starter

Michael Johnson

We have a system that consist of the Allen-Bradley's ControlLogix 5550 processor, some ControlNet bridges, a Allen Bradley PLC5/20C with the SST Profibus coprocessor, about 50 Siemens SIMOCODEs, and six Siemens Master and MicroDrives. We require about a maximum of 1700
to 2000 bytes of data to send over the ControlNet to the SST processors in a deterministic and consistent manner. If we did not care about
speed/response time, we would just transmit and receive in the unscheduled bandwidth. But, since
speed and response is an issue we want to send this on the scheduled bandwidth. Well the only way to do this is to create producer and consumer type tags to send and receive between the PLC5/20C and the ControlLogix processor. Well there is a problem with that because, there is a 500 byte limit. So, we decided to use a multiplexing/de-multiplexing scheme inwhich we send and receive data to the PLC5/20C one motor at a time through the scheduled bandwidth. This works up to a point, it seems that every once in a while data that is a signed to a specific location will end up some where else. We are using sequencers and timers to control the sending and receiving data and a 20 millisecond RPI. My question is this: is there a better way to send and receive 1700 to 2000 bytes of data between processors on ControlNet?