Path: utzoo!attcan!uunet!cs.utexas.edu!usc!ucsd!sdd.hp.com!hplabs!hpfcso!hpldola!hpctdlb!hpctdls!wei From: wei@hpctdls.HP.COM (Bill Ives) Newsgroups: comp.sys.ibm.pc Subject: Re: INPUT PARALLEL DATA OVER THE PRINTER PORT? Message-ID: <2010023@hpctdls.HP.COM> Date: 18 May 90 15:19:30 GMT References: <7459@arctic.nprdc.arpa> Organization: Hewlett-Packard CTD, Colo. Spgs. Lines: 35 >/ hpctdls:comp.sys.ibm.pc / trejo@nprdc.navy.mil (Leonard J. Trejo) / 10:05 am May 16, 1990 / >We're setting up a communications scheme between two PC's >for a real-time data acquisition application. I'm just wondering, >although the bios innterupt 17H does not have a service request >for parallel input, might there be another way to force the >printer port to take parallel input coming from another PC? >Please reply or copy to me via e-mail. Thank you. Since this may be of interest to others beside yourself, I have elected to respond rather than email. Although it is true that the parallel port interface chip set could handle input (as well as output), when IBM originally designed it they did not allow (very well at least) for input in their hardware. This "flaw" in their design has to do with pull up resistors on the input lines ( which are too small ) thus any input will generate a signal voltage which will cause a current to sink into the actual chip set input lines. Since the chips are only rated to sink a few uAmps to a few mAmps, reading from the parallel port could be potentially dangerous. Of course, the lower the rating, the more dangerous it is to read. Now, some manufacturers design their parallel port interfaces to handle input, but you should check before trying it. My guess is that parallel input has never caught on due to it not being possible on original IBM equipment (actually burning it out -- I've done it so I know). Hope this helps some.... Bill Ives HP CTD #include