My first wire wrap: Wilf's AT keyboard interface

[mrtinb]

Hi

I'm trying to create Wilf's AT keyboard interface http://www.user.dccnet.com/wrigter/inde ... XATKEY.htm http://wilfr.000webhostapp.com/index_files/ZXATKEY.htm .

It's my first time trying a project with wire wrap. It's cool you can modify without soldering and reuse the parts in the final design. But I didn't expect the wire wrap sockets to be SO expensive. It's mostly because I can't buy them cheap in China but from local old storage with high prices.

[1024MAK]

Yeah, there are lots of advantages to wire wrap. However, one painful thing is if you have to remove(unwrap) a wire on the "bottom" of a pin due to a mistake/error/change of mind after wrapping one or more other wires further along the pin...

And when properly constructed, a wire wrap board can have a service life of 30 or more years

Mark

[mrtinb]

You can just cut the bottom wire if there's room above

[mrtinb]

I've redesigned the board after I got hold of a wire wrap version of the edge connector. There's still a lot to wire.

[gammaray]

Exactly the reason to wirewrap, you can change your prototype!

Nice!

Were you able to find the program mentioned "keyb18xa.bas" or starting without?

Found this...
https://www.phanderson.com/picaxe/

[mrtinb]

My plan is to replace it with an Arduino Pro Mini, but this first version will just have the DIP switches to see the concept working.

[mrtinb]

So now the wires have been wrapped and this is the first prototype with DIP switches in place of Arduino controller and keyboard.

[mrtinb]

Wilf's AT keyboard (and backup copy here) uses only A0, A8 to A15. That means he reads these addresses:
11111110???????0
11111101???????0
11111011???????0
11110111???????0
11101111???????0
11011111???????0
10111111???????0
01111111???????0

That does not give I/O $FE, because all he ensures is that circuit answers to 0 in lowest bit. A1 to A7 is not connected.

Does his circuit not miss an address decoder so the circuit is only enabled on I/O $FE?

[PokeMon]

It is typical for the ZX81 that there is no full address decoding used and keyboard responds to all i/o addresses with D0=0.

[mrtinb]

But wouldn't this interface conflict with any other device with A0=0? Wouldn't it conflict with any device with even I/O address?