My first wire wrap: Wilf's AT keyboard interface

Discussions about Sinclair ZX80 and ZX81 Hardware
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gammaray
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Re: My first wire wrap: Wilf's AT keyboard interface

Post by gammaray » Mon Feb 12, 2018 1:03 am

Just thinking through this puzzle...

If RAMTOP was 24xxx with external /RAMCS for an 8K RAM then you would see activity on A13?

The keyboard only uses this for "YUIOP" which is keyboard matrix 5 of 8 x 1,2,3,4 or 5.

So it would always be LOW except for keyboard routine when HIGH and all but one of A8,9,10,11,12,14,15 go LOW to pull down KBD0-4.

That means that the EPROM A5 is grounded not HI-Z and A13 always reads low?

Is there a short to ground?
Last edited by gammaray on Mon Feb 12, 2018 2:08 am, edited 1 time in total.
Finish what you start. Truth is over the mountaintop or six feet under.
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gammaray
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Re: My first wire wrap: Wilf's AT keyboard interface

Post by gammaray » Mon Feb 12, 2018 1:05 am

I think I have learned at lot at SinclairZXworld!
Finish what you start. Truth is over the mountaintop or six feet under.
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1024MAK
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Re: My first wire wrap: Wilf's AT keyboard interface

Post by 1024MAK » Mon Feb 12, 2018 1:12 am

The keyboard uses the Z80's I/O instructions. It is documented (but only in some of the Z80 documentation) that when an I/O instruction puts an address on address bus lines A0 to A7, it also puts a value on address lines A8 to A15.

What is put on these depends on the instruction. For example: IN A,(C) actually puts the contents of the B register on A8 to A15. So the address used with I/O instructions are actually 16 bit values. Sinclair used A8 to A15 to form part of the lines going to the keyboard (remember, the keyboard is a matrix).

So it would be the Z80 running the keyboard routine in ROM that would result in the Z80 driving A13.

Mark

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gammaray
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Re: My first wire wrap: Wilf's AT keyboard interface

Post by gammaray » Mon Feb 12, 2018 1:23 am

There is a smudge on perfboard at A13. Could that be copper residue causing grounding?
at key project short.jpg
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Finish what you start. Truth is over the mountaintop or six feet under.
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gammaray
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Re: My first wire wrap: Wilf's AT keyboard interface

Post by gammaray » Mon Feb 12, 2018 1:31 am

This looks suspicious to the left of the yellow A5-A13 connection.

But I have never done wirewrap.
close wirewrap.jpg
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Finish what you start. Truth is over the mountaintop or six feet under.
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Re: My first wire wrap: Wilf's AT keyboard interface

Post by gammaray » Mon Feb 12, 2018 3:19 am

On your schematic Is /WE the same as programming voltage? Vpp? Should it be low instead...
27C256.gif
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I didn't realize there were so many balls on the table.
Finish what you start. Truth is over the mountaintop or six feet under.
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Re: My first wire wrap: Wilf's AT keyboard interface

Post by mrtinb » Tue Feb 13, 2018 9:49 am

gammaray wrote:
Mon Feb 12, 2018 1:31 am
This looks suspicious to the left of the yellow A5-A13 connection.
I'll look into that
Martin
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube

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Re: My first wire wrap: Wilf's AT keyboard interface

Post by mrtinb » Tue Feb 13, 2018 9:50 am

gammaray wrote:
Mon Feb 12, 2018 3:19 am
On your schematic Is /WE the same as programming voltage? Vpp? Should it be low instead...27C256.gif

I didn't realize there were so many balls on the table.
The text drawing is the original one from Wilf Rigter that uses an EPROM. I've modified it to use an EEPROM seen the the schematic in former post.
Martin
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Re: My first wire wrap: Wilf's AT keyboard interface

Post by mrtinb » Tue Feb 13, 2018 9:56 am

Currently I think the problem lies with the "diode OR gate" where both A0, RD and IOREQ has to be low, for OE on EEPROM goes low.

It needs a little more time and a clear mind. Today that is FALSE. ;-)
Martin
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube

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gammaray
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Re: My first wire wrap: Wilf's AT keyboard interface

Post by gammaray » Tue Feb 13, 2018 7:40 pm

I hope I am not hindering that
Finish what you start. Truth is over the mountaintop or six feet under.
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