ZX81 joystick interfaces

Discussions about Sinclair ZX80 and ZX81 Hardware
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1024MAK
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Re: ZX81 joystick interfaces

Post by 1024MAK » Sat May 27, 2017 4:21 pm

1024MAK wrote:
Fri May 26, 2017 8:51 pm
IIRC, there is a thread on here somewhere with some details of some less common joystick interfaces. And of course, just like on the ZX Spectrum, some people wired a joystick port to the keyboard connectors.
ZXpand joystick thread here ;)
It does include some comments about other joystick interfaces.

Mark

Tezz
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Re: ZX81 joystick interfaces

Post by Tezz » Sat May 27, 2017 7:17 pm

Thanks Mark, that's a shame that they turned out to be poorly implemented Kempston interfaces :roll: I was going to take a look into the other interface to see where that disconnected black wire came from :) thanks for that, I guess that along with the other issues you noticed is the reason why that one has a label taped to the back with "U/S" on it :mrgreen: With that important design flaw I don't suppose these interfaces will be much good to anyone.

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1024MAK
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Re: ZX81 joystick interfaces

Post by 1024MAK » Sat May 27, 2017 7:38 pm

Tezz wrote:
Sat May 27, 2017 7:17 pm
Thanks Mark, that's a shame that they turned out to be poorly implemented Kempston interfaces :roll: I was going to take a look into the other interface to see where that disconnected black wire came from :) thanks for that, I guess that along with the other issues you noticed is the reason why that one has a label taped to the back with "U/S" on it :mrgreen: With that important design flaw I don't suppose these interfaces will be much good to anyone.
We can rebuild it. We have the technology. We can make it better than it was. Better, stronger, faster....
Okay, maybe not stronger, faster.... but we can improve the decoding and fix some of the problems. But the question is, are you up for it?

Mark

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Re: ZX81 joystick interfaces

Post by Tezz » Sat May 27, 2017 8:08 pm

I'll be up for that, better than the other option of landfill :D

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Re: ZX81 joystick interfaces

Post by Moggy » Sat May 27, 2017 9:18 pm

That's the spirit lads!! :D

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1024MAK
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Re: ZX81 joystick interfaces

Post by 1024MAK » Sun May 28, 2017 12:17 pm

Okay Tezz...
back edited 04.jpg
Joystick Interface modifications - part 1
back edited 04.jpg (1.2 MiB) Viewed 259 times
Mark

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Re: ZX81 joystick interfaces

Post by Tezz » Sun May 28, 2017 7:37 pm

Thanks Mark, I'll try and make some time in the morning to work on that :) Will I need any components?

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1024MAK
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Re: ZX81 joystick interfaces

Post by 1024MAK » Sun May 28, 2017 7:54 pm

If all three chips work okay, hopefully all you will need is wire and solder.

By using all three NOR gets in the 4025 chip, we can do a little rewiring so that /RD and A6 get included in the address decoding. That assumes that the 4025 chip is fast enough (as three gates will be cascaded). [I have done a similar mod. on another joystick interface, but can't remember if it used a 74LSxxx logic chip or a CMOS logic chip...]

I have no idea why the 150 ohm resistors were added. The existing 560 ohm resistors should have been fine.

The only concerns I have are: did any of these interfaces ever work? The chips used are 4000 series CMOS logic chips, which are not very fast when operated on a 5V supply.
And after having one of it's outputs shorted, is the 4025 chip still fully operational?

But all that is unknown unless we try :mrgreen:

We will start with some static logic tests.

Mark

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mrtinb
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Re: ZX81 joystick interfaces

Post by mrtinb » Wed Dec 20, 2017 8:01 pm

There seems to be a Kempston Joystick Interface on sale on eBay right now if anyone is interested.

https://www.ebay.co.uk/itm/Sinclair-ZX8 ... SwUYNaDZ2G
Martin
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube

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