Hello! I hope this topic is accepted in this board, as I couldn't find a particular support forum for NI hardware.
Years ago, we developed a GPIB interface board, using a NAT7210 GPIB controller which is hosted by an Atmel 8 bit MCU. For a test, the board is connected to a NI GPIB PCI interface, using MAX and NI-488 Communicator for communication.
Everything works fine so far, except one thing: a customer complained about occasionally "distorted" responses to the *IDN? query. We verified this to be true.
The response sometimes contains one additional character. For example, if the response string to the *IDN? query would be
70 bytes (including end token 0xA), sometimes it is 71 bytes and the additional character, which is mostly a ">" (0x3E), is inserted in random position.
Sometimes it's even worse. Then the NAT7210 sends the string twice, making it 139 bytes.
This error occurs every few times when querying *IDN?.
The MCU that controls the NAT7210 does not send these additional character. I can verify in the debug mode, that the buffer content that is send to the GPIB controller is OK and the code is OK so that sending data is not interfered. We don't have any clue how to stop this.
The NAT7210 has no command to flush its output buffer, nor we know if it does automatically after sending the message via GPIB.
Does anybody have any idea what's causing this and how to stop it?