Does the serial command 'SetComTime' affect data in the I/O buffers, or can the timeout value be changed on the fly?

[Mike Evans]

I have various serial sub-routines that ideally require different timeout values. The main CVI program is testing eight units under test asynchronously using the 8-port NI serial card. Occasionally (after 8 hours or more of running) I get unexplained data loss - could this be due to me changing the serial port timeout values with unread data in the buffers or should I look elsewhere?

Thanks in advance - Mike Evans

[Randy Solomonson]

Hello-

This could be caused by many different circumstances. sysinternals.com has a handy utility, portmon. This utility can capture all calls to the serial driver in Windows. This utility may provide more details about the cause of such an error.

A typical cause is a buffer overrun. This is typical for a Windows 98 system. The operating system is slow to service the interrupts and the buffer built into the UART is full when more data is received.

Another alternative is to use VISA. Serial VISA calls can be captured by NI-Spy and portmon. NI-Spy has a few more features than portmon. In NI-Spy, the calls that cause errors are red in color.

Randy Solomonson
Application Engineer
National Instruments