Jiju,
Using of Parallel port u can't read the voltage if u want to read voltage u should put a parallel ADC (0804) and read external voltage. if u want to access the port u have to set some of the registers. the registers are following on
1. Data Register (Base Address)
2. Control Register and (Base Address + 1)
3. Status Register (Base Address + 2)
If u set the bit 0 in Data Register u can access a 5V DC in pin 2 and ground pin 25. The example vi following on
C:\Program Files\National Instruments\LabVIEW 2010\examples\portaccess\parallel port examples.llb\Parallel Port Read and Write Loop.vi
Siva
Sivaraj M.S
CLA