Attached is a ZIP file containing edited versions of your VI.
I have included a control on the sub-VI that allow the main VI to specify which I/O point each call is going to act on.
I have also included some notes in the sub-Vi that recomend breaking up the sub-VI into three parts.
1) Sets up the I/O.
2) Write and read I/O point
3) Close connections to I/O device.
As in my previous posts, these are simplified suggestions. Elegent solutions should be implemented to do this correctly. But, this comes latter.
Ben