Hello,
Is there any downside with this simple external ROM extension board? It would be much cheaper for diagnostics than the ZX DIAG CART.
I am assuming it'll work with ZX Spectrum 48K clones, not only with ZX Spectrum 48 / 128 / +2 / Timex 2048.
External Diagnostics ROM
External Diagnostics ROM
Valentin
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Re: External Diagnostics ROM
Most of the diagnostic boards available are enhancements of the original design, which is on this web site. There was some discussion way back in 2014 on what extra features were to be included on WoS forums. But someone went further. Obviously as it gets more complex, the cost goes up.valentin wrote: ↑Mon Jan 03, 2022 7:01 pm Hello,
Is there any downside with this simple external ROM extension board? It would be much cheaper for diagnostics than the ZX DIAG CART.
I am assuming it'll work with ZX Spectrum 48K clones, not only with ZX Spectrum 48 / 128 / +2 / Timex 2048.
You can use ANY interface which maps a 16k byte ROM (or a 16k byte area of a larger ROM) into the address space of the BASIC ROM. There are a number of expansions/interfaces that can do this.
As per your question, I don’t like that the linked to ROM board ignores the Z80 /RD control line (*1) even though there are THREE spare logic gates. Apart from ignoring standard Zilog Z80 design practice (*1), I don’t see any other problems.
Note *1: normally the Z80 /RD control line should go to a memory chip’s /OE input. Address decoding should be performed by suitable logic (gates or other suitable logic), then combined with the Z80 /MREQ control line with more logic. The output of this logic then controls the memory chip’s /CS or /CE pin.
If a clone or compatible computer has the exact same signal allocation on it’s expansion port / edge-connector AND taking the /ROMCS line logic high disables the on board (BASIC) ROM, yes, it should work.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
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Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: External Diagnostics ROM
Cheers, Mark.
And I understand your observation about the Z80 best practices.
I have ordered on eBay a similar board as the one linked in my original message - they are the same, the one I ordered has SMD components.
And I understand your observation about the Z80 best practices.
I have ordered on eBay a similar board as the one linked in my original message - they are the same, the one I ordered has SMD components.
Last edited by valentin on Wed Jan 05, 2022 10:43 am, edited 1 time in total.
Valentin
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Re: External Diagnostics ROM
Your link is incorrectly formedvalentin wrote: ↑Tue Jan 04, 2022 12:05 pm I have ordered on eBay a similar board as the one linked in my original message - they are the same, the one I ordered has SMD components.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.