Oh no! Not another ULA.

Any discussions related to the creation of new hardware or software for the ZX80 or ZX81
Lardo Boffin
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Re: Oh no! Not another ULA.

Post by Lardo Boffin »

Looking awesome. 8-)

I have several zeddies in need of a ULA based rescue so happy days!
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Paul
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Re: Oh no! Not another ULA.

Post by Paul »

With those free bits, could you offer faster turbo modes?
This way we could try out up to which speed our Zeddy still works :mrgreen:
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Andy Rea
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Re: Oh no! Not another ULA.

Post by Andy Rea »

Paul wrote: Mon Sep 04, 2023 7:52 am With those free bits, could you offer faster turbo modes?
This way we could try out up to which speed our Zeddy still works :mrgreen:
You Want Quad speed ? in theory should work.. BUT you WILL need a faster CPU and The MOTOROLA type rom (or your own fast replacement) the NEC roms dont even work at double speed !

Bngger!!! :roll: :roll: the motorola rom is too slow also.
what's that Smell.... smells like fresh flux and solder fumes...
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Paul
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Re: Oh no! Not another ULA.

Post by Paul »

My ROMs are 45ns and my CPU 20MHz :ugeek:
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Andy Rea
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Re: Oh no! Not another ULA.

Post by Andy Rea »

Paul wrote: Mon Sep 04, 2023 1:07 pm My ROMs are 45ns and my CPU 20MHz :ugeek:
That will be plenty fast :mrgreen:

I haven't done any calculations but can tell you that a 250ns eeprom ( at28c64-25pc) works okay
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Paul
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Re: Oh no! Not another ULA.

Post by Paul »

And in case you are not short of macro cells:
I would like to have a WR signal that doesn't come active in the lower 8K address space.
So I could use a 32K Autostore RAM as combined ROM and RAM (RAMCS and ROMCS ORed) in order to have a three chip zeddy :geek:
I once tried and it worked but could not be reseted because the bottom 5 bytes are overwritten.
As the ROM content was locked it needed a power cycle to restore the ROM again.
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Andy Rea
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Re: Oh no! Not another ULA.

Post by Andy Rea »

Paul wrote: Mon Sep 04, 2023 1:30 pm And in case you are not short of macro cells:
I would like to have a WR signal that doesn't come active in the lower 8K address space.
So I could use a 32K Autostore RAM as combined ROM and RAM (RAMCS and ROMCS ORed) in order to have a three chip zeddy :geek:
I once tried and it worked but could not be reserved because the bottom 5 bytes are overwritten.
As the ROM content was locked it needed a power cycle to restore the ROM again.
Would altering ROMCS to be only active when ~RD is low also ? have any impact on other things ?
what's that Smell.... smells like fresh flux and solder fumes...
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Paul
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Re: Oh no! Not another ULA.

Post by Paul »

That sounds like another possible solution. Great idea!
This way I just connect normal !WR directly and RAMCS and ROMCS via diodes.
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Andy Rea
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Re: Oh no! Not another ULA.

Post by Andy Rea »

i forgot about fetching character data during the refresh when the screen is been drawn...
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1024MAK
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Re: Oh no! Not another ULA.

Post by 1024MAK »

If we don’t find any better uses for spare bits, if there are spare output pins, maybe use for Blinkenlights :P

This would normally be under software control, hence the Zeddy could gain a very simple output. If you don’t want a Blinkenlight, it could drive something else via suitable circuitry (transistor) such as a relay.

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