Why does the MSB toggle in serial mode when parity is enabled?

[Neumannium]

Hello everyone,

I created a small VI to read 1 byte of data across an RS-422 port. The data is then passed via a queue to another VI which displays the byte read.

I have been testing the functionality of the VIs using HyperTerminal, and they seem to be OK when I have the parity in the VI and HT set to 'none'. When I set it to 'odd' or 'even' parity, however, the most significant bit toggles at every send. That is, when I repeatedly hit the spacebar, I get alternating values back of 0x20 and 0xA0.

Does anyone know why it is doing this? I'm assuming it's something simple that I'm just missing, but I cannot figure it out.

I've attached the 2 VI's so that you can try this yourself. (c
reated in LabView 7 Express)

Any help is greatly appreciated!

Dave Neumann

[Chris_Rake]

We routinely see this behavior with hyperterm where the MSB alternates with both built-in and add-in COM ports across different brands of serial hardware. I believe this is a bug in the hyperterm application itself and not related to LabVIEW since we can reproduce it using two hyperterm sessions.