gulukota@brahms.amd.com (Karunakar Gulukota) (06/05/91)
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. Thanks, Karunakar Gulukota
dougc@bert.cs.byu.edu (DOUG CANNON) (06/05/91)
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.