We don't have NI TestStand so supporting you is difficult, however I think there is a fundamental problem. The way it should work is this:
- load DLL
- call connect telling the DLL you want to use COM1 and 115200
- call blankcheck
- call disconnect
- unload the DLL
So to answer your question blankcheck knows to use COM1 because you have already called connect telling it to use COM1. The key thing is that the DLL remains loaded from beginning to end. If you do this:
- load DLL
- call connect
- unload DLL
- load DLL
- call blankcheck
- unload DLL
Then it won't work. So you will need to double-check when TestStand is loading and unloading the DLL for you.
Also 115200 is quite high. I would suggest you start off more conservatively at 19200 and work your way up. Although it does appear to be working for you.
Andy