MaxCoderz

I've built a number of parallel cables to date, none of which have worked!

I've been using the diagram that can be found in the TI Link Protocol and File Format guide.

Each data line is controlled like this:

PI = parallel input, PO = parallel output, T = TI's input/output, M = midpoint.

My understanding is that when neither device wants to hold a line low, PO is high and T is high.
No current can flow through the diode (no potential difference across it), and so PI is held high and can be seen as such by both ends.

If the PC wishes to hold a data line low, it pulls PO low. Current flows from the calculator and through the resistor and diode into PO. Current also flows from PI through the diode into PO. Both devices can therefore see the line is low.

If the calculator wishes to hold a data line low, it pulls T low. I believe the idea is so that current can flow from PI, through the resistor and so appear that the line is being held low. Even though PO will be held high, current cannot flow backwards through the diode and so won't affect the reading.

Problem: even though the voltage at T is 0V, it's still ~2.7V at M! The resistor is not allowing sufficient current to be drawn from PI, and so the PC thinks that PI is still held high.

I have tried the above circuit on at least four machines, and it has worked on none of them. By simply removing the resistor (so M is directly connected to T) the cable works perfectly.

Has anyone here assembled the circuit and got it to work on their machine?

In case its funky components on my end, the resistors are cheap 1K quarter Watt affairs, and the diodes are equally budget 1A silicon rectifier 1N4001s.

I have made this cable twice a few years ago, and it didnt work either. I think i still have one of them lying around, ill remove the resistor and see how it goes! .

I finally built one of these but it is not working for w/e reason. Though after testing It may be an issue with TiLP and not the cable.

p.s. sorry for the necro post but I would love to have a cable other than my usb ones working.

Make sure you run TiLP with administrator privileges. I can't really guess what the problem is without more information, I'm afraid. :\

Mine's worked since about 2000 using the design featured on ticalc. It's either using 1N4148 or 1N914 diodes which both have a higher Vf than the 1N4004. I don't know how much the TI-82 I/O differs from the 83+/84+, but it could be a sign that the new calcs have lower input impedances than the mid 90's stuff. Or who knows? Maybe it's the parallel ports that are different.

It's quite possible. I've built about three different cables and tried them on six different PCs, the only constant factor is using rectifier diodes rather than signal diodes.

Hmm, well I couldn't get it to work but thanks for the help Benryves.