AT-cards make some response to most of the commands that are issued to them. Using a terminal, these commands are received and shown immediately. Commands can also be sent to the AT-cards from higher-level languagess such as Visual Basic and LabView. Unless programmed to do so, these higher-level languages do not read the responses back. The AT-cards then put these responses into an output buffer which can eventually fill up. Once this output buffer fills up, the card then will lock up until it is emptied.
There are two ways to rectify this:
1) Using the higher-level language, read all of the responses out of the output buffer until it is empty.
2) Turn off the responses with the ERRLVL command set to zero.