ZX81 joystick interfaces

Discussions about Sinclair ZX80 and ZX81 Hardware
Tezz
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ZX81 joystick interfaces

Post by Tezz » Fri May 26, 2017 7:56 pm

Hi all,

I managed to buy a couple of ZX81 joystick interfaces this week. Does anyone know anything about these particular ones? Both of them had no front part of the casing. Are they perhaps home made?
ZX81_joystick_interface1.png
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Tezz :)

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1024MAK
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Re: ZX81 joystick interfaces

Post by 1024MAK » Fri May 26, 2017 8:47 pm

Hi Tezz

Please ensure you are sitting down.

There are no joystick interfaces for the ZX81 or the TS1000. The ZX81 / TS1000 was never used for game playing. These computers are serious machines, typically used for controlling nuclear power stations.

Back to the serious stuff, back in the day, there was no "standard" joystick interface for the ZX81/TS1000. There may well have been joystick interfaces made for ZX81/TS1000 machines. Most would have been a small scale production. Made by small businesses or even made at home in a workshop.

Fast forward a few years, and the ZX Spectrum came along. A number of joystick interfaces were made for the ZX Spectrum. Soon the Kempston "standard" took off. Now, back then, ZX81/TS1000 sized edge-connector sockets were less expensive than the size used by the ZX Spectrum. As these joystick interfaces (for the ZX Spectrum) did not need all the connections on the ZX spectrum edge-connector, manufacturers found they could use ZX81/TS1000 edge-connectors.

The upshot is that now, unless they are marked, or come in the correct packaging (box), it is often not possible to tell at first if a joystick interface that uses a ZX81/TS1000 edge-connector was actually intended for a ZX81/TS1000 or was intended for a ZX Spectrum... :roll:

For example, I have a number of Kempston compatible joystick interfaces with a ZX81/TS1000 edge-connector. As far as I can tell, these (as in all Kempston compatible joystick interfaces) were only ever sold for the ZX Spectrum. Although they do work okay on a ZX81/TS1000.

If you want to know more about your interfaces, please post photos of your interfaces. Front and back. We need hi quality pictures so that we can see the numbers on the chips and details the PCB tracks, so we can see which pin of which chip connects to the edge-connector etc...

Mark

Moggy
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Re: ZX81 joystick interfaces

Post by Moggy » Fri May 26, 2017 9:07 pm

I seem to remember a "programmable" one for the 81, the programming amounting to nothing more than a few jumper leads here and there. :lol:

Plus a thread here re 81 joysticks albeit no longer sold I believe.

viewtopic.php?f=6&t=1131
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siggi
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Re: ZX81 joystick interfaces

Post by siggi » Fri May 26, 2017 9:17 pm

1024MAK wrote:
Fri May 26, 2017 8:47 pm
Hi Tezz

Please ensure you are sitting down.

There are no joystick interfaces for the ZX81 or the TS1000. The ZX81 / TS1000 was never used for game playing. These computers are serious machines, typically used for controlling nuclear power stations.
Indeed. And here is the nuclear power station control program:
harrburg.p
(7.47 KiB) Downloaded 15 times
:mrgreen:
Siggi

PS: AFAIK not compatible to any known joystick interface ...
My ZX81 web-server: online since 2007
http://zx81-siggi.endoftheinternet.org/index.html

Tezz
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Re: ZX81 joystick interfaces

Post by Tezz » Fri May 26, 2017 9:29 pm

Thanks guys, I'll take some better hi-res photos in the morning hopefully with both sides of the PCB. You are right Mark that I assumed they were interfaces for the '81 because of the edge connector :) With several ways to implement a joystick interface and no set standard, is there a list of games supporting various methods? Also maybe some patched earlier titles?

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1024MAK
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Re: ZX81 joystick interfaces

Post by 1024MAK » Fri May 26, 2017 9:51 pm

In terms of today's world, some games exist that use a Kempston joystick interface. But most modern, as in recent software supports the ZXpand joystick interface (the Joystick D-connector is part of the ZXPand-AY Sound Module board for older versions, but it was possible to wire your own connector to a ZXpand).

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.

Mark

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1024MAK
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Re: ZX81 joystick interfaces

Post by 1024MAK » Fri May 26, 2017 10:18 pm

Moggy wrote:
Fri May 26, 2017 9:07 pm
I seem to remember a "programmable" one for the 81, the programming amounting to nothing more than a few jumper leads here and there. :lol:
Thanks Moggy

I was aware that AGF made a Joystick interface for the Zeddy, but info about it on the internet is hard to find...

Mark

Tezz
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Re: ZX81 joystick interfaces

Post by Tezz » Sat May 27, 2017 1:06 pm

Here's a couple of closer photos of the front and back of the pcb :)
front.png
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back.png
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1024MAK
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Re: ZX81 joystick interfaces

Post by 1024MAK » Sat May 27, 2017 5:11 pm

Yep, this joystick interface looks like a crude Kempston compatible one.

Even though it uses a 4025 triple 3-input logic chip for the address and control decoding, only one of the three 3-input NOR gates is being used. So the partial decoding is only when A5 is low (0), A7 is low (0) and /IORQ is active (low).

Kempson interfaces vary from only needing A7 low (0) to having all 8 bits of address lines A0 to A7 correctly decoded. But ZX Spectrum software is written to use port 31 (dec) 0x1F (hex).

The interface will respond if the CPU tries to write to any I/O port address with A5 and A7 low, as it ignores the Z80 /RD control line. Writing will cause a bus collision as the Z80 and the 4066 chips both try to outdrive each other (read as the 4066 shorting out the CPU) which is poor design :evil:

With this design, it looks like pin 8 (common) on the 9-way D-connector is connected to +5V. So don't try to use an autofire joystick. Pin 8 is normaly 0V/GND on Atari machines.

There are some strange things with this interface. First, despite there being five 560 ohm pull down resistors (those on the front of the board), four extra 150 ohm pull down resistors have been soldered to the track side in parallel with four of the 560 ohm resistors. Why add these? And why only four? The down direction input does not have an extra 150 ohm resistor.

In the photos, I presume the black wire has come adrift from pin 8 of the 9 way D-connector.

The tracks for the pins of the 4025 chip look like pins 1 to 7 are all connected together, but pin 6 is an output pin! [pins 1 to 5 are inputs and pin 7 is the GND pin for the chip]. I also can't see the track connecting this group to the 0V/GND rail. But it may just not be visible in the photo.

And last, edge-connector pins 10 and 11 look like they have either got a track between them, or a bit of solder. One is a data line (pin 10), the other is the /INT pin. They should not be connected together.

Mark

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1024MAK
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Re: ZX81 joystick interfaces

Post by 1024MAK » Sat May 27, 2017 5:14 pm

BTW, more info on ZX Spectrum joystick interfaces over on WoS here ;-)

Mark

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