The Art of Assembly Language book, Borland C/C++ compilers, and the DJGPP compiler provide ample documentation and functions for parallel port output. But what about parallel port input? Here I go a-searching the Internet to find the pertinent information.
20190617/DuckDuckGo dos read input from parallel port
20190617/http://electrosofts.com/parallel/
20190617/https://en.wikipedia.org/wiki/Parallel_port
Well, as it turns out, input is easy to do, just make sure to set bit 5 of the control register, then you can read and write the port both ways from the data register, as indicated in the following table.
| Register | LPT1 | LPT2 |
|---|---|---|
| Data register (Base Address + 0) | 0x378 | 0x278 |
| Status register (Base Address + 1) | 0x379 | 0x279 |
| Control register (Base Address + 2) | 0x37a | 0x27a |
Well, apparently Borland C/C++ does include functions for parallel port input. Look toward the outportb() inportb(), outport(), and inport() functions.