Is this actually for the ZX81? AGF Joystick Interface II

[system11]

Sold to me as a ZX81 interface, definitely doesn't seem to do anything - is this genuinely for the ZX81? It came with AGF labelled sticks too, I've photographed such that you can see which pins actually have solder on the PCB.

[1024MAK]

There were versions for both the ZX81 and the ZX Spectrum.

By the looks of it, as yours has the ZX81 sized edge-connector, it appears to be the ZX81 version.

See the listing on Spectrum Computing here.

The details in the advert should help. But basically the first joystick port simulates the curser keys and the zero key. The second port simulates some other keys on the keyboard.

Some good quality photos for use on Spectrum Computing (which also covers the ZX81) would be nice. Would you be willing to either upload them to a photo sharing site or send via email to me and give permission for me to them upload them for use on Spectrum Computing? Or maybe you would like to do that yourself.

If it’s not working, it’s possible that one of the chips is faulty. As these early joystick interfaces are fairly simple, most faults are not difficult to fix if you can solder. Alternatively, I could see if I could fix it if you want me to.

Mark

[1024MAK]

Having looked at the circuitry and the way it is wired, this version of the interface may need the joysticks supplied by AGF for use with this version. It looks like it’s not compatible with ‘standard’ Atari type joysticks.

The clues are in the adverts (see the link in my earlier post) where they talk about an improved version and where in the part about buying their Atari joysticks, they say that for the first version of the interface, specify OLD when ordering joysticks.

Combined that makes me think that they modify the joysticks for use with the first version (like you have) of the interface.

Mark

[system11]

I can try to get a better photo more suited to a website, no problem.

If it was working, should I expect this to emulate cursor keys? I'm trying to work out if I've been sent what was advertised or not. It's already not what I intended to buy as it came with the programmable version note cards and I saw those and just clicked without thinking. So it's either "you bought the wrong thing and got it bad luck" or "you bought the wrong thing and didn't even get what was advertised".

As far as I can see it is using the following pins:
+5v, GND, A0, A10, A11, A12, A13, D0, D2, D3, D4, /RD, /IORQ

The 'enable' switch will either tie /E1 and /E2 of the 74LS365 high which would isolate the outputs, or to the output pin 6 of the 74LS32.

I received two AGF modified sticks but it doesn't say new or old on the label. I'm not sure what AGF did to them, all I can tell without opening one which right now I'd like to avoid, was verifying that the pins in use match the ones on the PCB. What seems to be approaching a common pin goes to A12 for Joy 1 and A13 for Joy 2, but it's not as simple as everything just shorting to common.

[1024MAK]

I can try to get a better photo more suited to a website, no problem.

That would be most helpful.

If it was working, should I expect this to emulate cursor keys?

Player 1 should be keys: 5, 6, 7, 8 and 0 for fire.
Player 2 should be keys: T, Y, U, I and P for fire.

I'm trying to work out if I've been sent what was advertised or not. It's already not what I intended to buy as it came with the programmable version note cards and I saw those and just clicked without thinking. So it's either "you bought the wrong thing and got it bad luck" or "you bought the wrong thing and didn't even get what was advertised".

What were you expecting?

As far as I can see it is using the following pins:
+5v, GND, A0, A10, A11, A12, A13, D0, D2, D3, D4, /RD, /IORQ

The 'enable' switch will either tie /E1 and /E2 of the 74LS365 high which would isolate the outputs, or to the output pin 6 of the 74LS32.

I agree. See the schematic I have drawn.

I received two AGF modified sticks but it doesn't say new or old on the label. I'm not sure what AGF did to them, all I can tell without opening one which right now I'd like to avoid, was verifying that the pins in use match the ones on the PCB. What seems to be approaching a common pin goes to A12 for Joy 1 and A13 for Joy 2, but it's not as simple as everything just shorting to common.

Yes. I think they may have added a diode in the joysticks. Because I can't see any way that the left direction would work otherwise. But this is just a guess.

Mark

[system11]

Ah that explains something, I wasnt able to check left with a meter.

Inside these there are 6 wires, normally it's common and 5 wires, very simple. However common for left is cut and theres a wire going to the non-common for down.

red+black = fire
green+blue = left
white+black = up
brown+black = right
blue+black = down

The confusion over the item is me thinking it was the programmable when I saw the program note cards (that come with the programmable jump wires one), which are obviously just something that got bundled. I failed to use my eyes and actually look at the perfectly clear photos of what it actually was. So this is entirely my fault assuming the interface really is a ZX81 compatible AGF plus sticks.

The pins the inferface is using - would those make sense for something essentially acting like keyboard presses? I know very little about the ZX81 hardware but I know the Memotech keyboard at least interfaces at the back.

[system11]

I'll check your schematic and supply the resistor values this weekend by the way.

[XavSnap]

10K ?

[1024MAK]

The pins the interface is using - would those make sense for something essentially acting like keyboard presses?

Yes, the connections make sense.

The ZX81 keyboard uses the upper eight address lines to scan the keyboard (under processor control) with A0 low.
As it's an I/O operation /IORQ and /RD are also low.

The ZX81 keyboard is arranged as an eight by five matrix. Five input lines go to the ULA, where they are put on the data bus (D0, D1, D2, D3 and D4) for the processor to read. 8 X 5 = 40.

Effectively on the actual keyboard you have a group of two "half" rows per row of the keyboard. Each "half" row being five keys.

That's what makes "cursor" key joysticks tricky. The number 5 key is in a different "half" row to the other keys (6, 7, 8 and 0).

Mark

[XavSnap]

Joy_AGF.pdf

(125.71 KiB) Downloaded 82 times

Not sure for the left cursor, D0 or D4 ?