Serial problem with LabWindows/CVI 8.0.1

[menchar]

Hi Mert -

Yup, nothing seems to be getting emitted by the serial port.

No error codes returned by any of the rs-232 library calls.

The inqueue size was like throwing a switch - less than 4097 bytes, everything's good, more than that, everything fails without error.

Menchar.

[menchar]

More info -

Same issue with a different machine, running Win2K.

We are using an rs-232 to rs-422  converter that is powered by the DTR line.  To enable the DTR, I use the call

ComSetEscape (Comport, SETDTR);

So if this call were to fail, no communications would take place, because the converter wouldn't be powered up.  Everything would look fine from the rs-232 perspective.

Does anyone know what the standard Windows serial driver is doing in re buffering decisions?    At one point, the CVI help said that WinNT always allocated a minimum of 4095 bytes.  NI has never stated, to my knowledge, what the effective maximum size is for input or output queues.

Does anyone know what the NI serial driver does in this case?   We have many NI serial cards, can I get deterministic, documented behavior if I use an NI serial card and the NI serial driver?

Thanks,

Menchar

[menchar]

Now I see another thread here discussing the issue with a response from Mert.

NI recommends an input queue size no greater than 32767.

It does mention "undefined behavior" when you exceed the serial driver's maximum inqueue size.   Our systems seem to be acting as if the maximum  inqueue size is 4096 bytes.

Menchar.