Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!think.com!spool.mu.edu!sol.ctr.columbia.edu!hamblin.math.byu.edu!news From: dougc@bert.cs.byu.edu (DOUG CANNON) Newsgroups: comp.sys.ibm.pc.hardware Subject: Re: Bidirectionality of the parallel port. Message-ID: Date: 5 Jun 91 00:39:23 GMT Article-I.D.: bert.DOUGC.91Jun4193923 References: <1991Jun4.200702.7276@amd.com> Sender: news@hamblin.math.byu.edu (Usenet News) Distribution: ca Organization: BYU, Provo, Utah Lines: 33 In-Reply-To: gulukota@brahms.amd.com's message of 4 Jun 91 20:07:02 GMT In article <1991Jun4.200702.7276@amd.com> gulukota@brahms.amd.com (Karunakar Gulukota) writes: > I thought that the data lines on the printer port can be used in the > bidirectional mode. The OE of the LS374, which is driving the data lines > of the parallel port, is grounded. In series with the outputs of LS374, > there are 30 ohm resisters, which I don't think are enough to keep the > source/sink currents into LS374 with in limits when the data lines are > driver by an external source. > > Can somebody shed some light on this problem. I am by no means an expert, but I have played a little with this. There seem to be many different types of parallel ports depending on your machine. I have here (just got it today) a KW-516E multi I/O card. It's parallel port is also driven by an LS374, but they give the option to have it be input or output. I just checked the OE (or Output Control, I think) and it connects directly to a jumper. The jumper can be changed to have this pin gounded (For Output) or, with the jumper in the other position, it seems to tie the OE of the LS374 to a Q (output) of a D flip-flop. It's hard to tell what this flip-flop is actually doing, but it probably is high. Thus the outputs of the LS374 are essentially disabled to allow input through the port. I haven't had time to play with this much as I just got the card today. I plan on hooking an A-D converter to the port to do various things. I think that you basically need a port with this (I/O) option, or you will be fighting with it, and the port usually wins. Maybe you should just install your own jumper. It ought to work--if not you can always re-solder it. > Thanks, > > Karunakar Gulukota No problem. Doug Cannon, BYU, Computer Science Dept.