We are working on a poll-response protocol using Concept 2.5 xxmit with a Modicon Quantum PLC. Polling (transmitt) looks great and the slave device responds (seen on protocol analyzer); however, we never get any data into the msg_in array. The oscilliscope shows that the slave response starts 3ms after the poll ends. When we reply manually to the poll using a laptop, the msg_in array is populated correctly and the bytes received counter shows the correct response length. Therefore, we've concluded that we have a timing problem (xxmit isn't ready to receive quick enough). Are best guess is to use command word 200h for the send, then change it to 480h as soon as the send is done without cycling the "start" input. Anybody know how to play with this better? Has anybody used xxmit for a poll-response protocol? If not, can anybody reccomend an industrial serial data buffer (24vdc or port powered, din rail mount) like the one they should have in the [email protected]%$& PLC?