A couple of questions.
1- Is the PC in the lab using the USB-485 converter as well? Does the old software use the same USB-485 converter.
2 - Does the laptop user always get the framing error or does the program work sometimes?
The user installed it on the laptop using an installer, which I would assume included LV runtime and VISA drivers, as well as the application.
As far as your comment about access times, shouldn't that information be transparent to me, the programmer? I mean, I check the number of bytes at the port before I read the port. And the old serial drivers don't seem to be affected...Perhaps I'm just not understanding the subtle nuances of what causes a framing error with NI hardware.
I just went back and looked at an installer for a similar program I wrote that runs standalone and used USB-232 adapter. I had put some notes to myself in the documentation.
You must have both LabView Runtime and NI-VISA Runtime installed on the target pc. It will not run without the NI-VISA Runtime.
The easiest way to rule out any potential differences between the PCI-485 and USB-485 is to use a USB-485 on your development system and see what happens.
I know, I know...you are probably tired of hearing you need to check the baud rate, parity, etc., but I'm just telling you what the description of an error is that I often receive.
A few questions...