used the CPU226 free port communication using send and receive commands, sending not a problem, but sometimes the data can be received, will then not often. The first I thought the problem is interference, but instead of using the computer when the PLC is very well received, and send the data without error, I suspect that programmers have problems. NA statement at the end I did not use interrupt procedures, procedures that would not lead to instability, NA, as we can ensure that every time in order to receive information.
There are PLC, reduced computer immediately sends the data in the response data received, send PLC and receive commands are no restrictions on the time interval will not be started not by order, as the data is transmitted completely, get with the result of failure.