I am using Windows 98 and a parallel port interface (25 pijn D-connector) to drive some lab prototypes for R&D purposes.
The interface allows me
(1) to output an 8-bit word on pins 2-9 and latch it in an 8-bit latch, using pin 1 to output a latch strobe;
(2) to read 5 bits in on pins 10,11,12,13 and 15; and
(3) to drive a 3-wire serial interface (chip enable, data and clock) using pins 14, 16 and 17.
I program it in assembler using IN and OUT instructions.
The problem is, when I toggle an input bit on pin 15 (bit 3, called n-Error/nFault in the case of a printer), I am seeing some spurious output on pin 16 that messes up the serially-controlled devices. Now, since these are adh=jacent pins, it may be a glitch due to cable coupling; I am checking for that now; but what I am also thinking is that I should have unloaded the existing Windows parallel port driver, as I suspect that it might be programmed to detect a change of nError/nFault and then send some output.
As I have not found anything on the web about the need to unload existing Windowa drivers before using the parallel port in your own way, please could somebody comment if they have a ssimilar experience, and tell us about this issue.
