ZX80 on ZX81???

Emulator and emulator development specific topics
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kokkiklhs
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ZX80 on ZX81???

Post by kokkiklhs »

I was looking at the superb dr beep's Sp-2-ZX80 emulator for the Spectrum and I just had a silly idea:
Could it somehow be ported to the Zeddy? Would this be possible?
:roll:

It would be an out-of-this-world experience to see an emulator running on Zeddy!
:lol:
Moggy
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Re: ZX80 on ZX81???

Post by Moggy »

Better still, solder 4 resistors to the right places on the CPU, program an EPROM with the ZX80's ROM code, fit a reset switch across the reset capacitor and have the real thing on a ZX81. :D
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kokkiklhs
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Re: ZX80 on ZX81???

Post by kokkiklhs »

Moggy wrote: Sun May 28, 2023 10:11 pm Better still, solder 4 resistors to the right places on the CPU, program an EPROM with the ZX80's ROM code, fit a reset switch across the reset capacitor and have the real thing on a ZX81. :D
Yes, I am aware of that (haven't tried it yet, though) but a 100% software emulator (IF such a thing is possible, I am not a programmer myself and was just wondering) would be a big programming achievement!! There could also be (in theory) e.g. a Jupiter Ace emulator for the Zeddy, AFAIK hardware-wise these machines are almost the same. Just checking the possibilities.

Another question: is there any other old, Z80 based monochrome and soundless system that could theoretically be emulated by a Zeddy? I know of the Tandy TRS-80 model I, but this has 32 and 64 character screenmodes, so this would be a major problem...
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1024MAK
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Re: ZX80 on ZX81???

Post by 1024MAK »

Although both the Jupiter Ace and the ZX81 both use the same microprocessor (Z80A or equivalent) and hence have ROM in the lower part of the memory map, and use a similar matrix keyboard, otherwise, the hardware is very different.

The ZX81 uses a mix of software and limited hardware to create a video picture. The Jupiter Ace video system is based on hardware, it will continue to produce a video image even if the processor is stopped (HALTed) or busy (unlike the Zeddy). Hence 2K bytes of the 3K bytes of RAM in a Jupiter Ace is for primary for the video system (only a small amount of video system RAM can be used for general purpose use).

That does not mean that an emulator can’t be written to run on a ZX81. But it does mean that there will be limitations, such as reduced speed.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

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Moggy
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Re: ZX80 on ZX81???

Post by Moggy »

1024MAK wrote: Mon May 29, 2023 4:03 pm

The ZX81 uses a mix of software and limited hardware to create a video picture. The Jupiter Ace video system is based on hardware, it will continue to produce a video image even if the processor is stopped (HALTed) or busy (unlike the Zeddy). Hence 2K bytes of the 3K bytes of RAM in a Jupiter Ace is for primary for the video system (only a small amount of video system RAM can be used for general purpose use).



Mark
Now that's something I didn't know! I always assumed Altwasser and Vickers just copied the Zeddy.
You wouldn't have a link to something that explains it in depth would you Mark or just a pointer so I can learn a bit more about it?

Thanks in advance. :D
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kokkiklhs
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Re: ZX80 on ZX81???

Post by kokkiklhs »

Moggy wrote: Mon May 29, 2023 4:58 pm
1024MAK wrote: Mon May 29, 2023 4:03 pm

The ZX81 uses a mix of software and limited hardware to create a video picture. The Jupiter Ace video system is based on hardware, it will continue to produce a video image even if the processor is stopped (HALTed) or busy (unlike the Zeddy). Hence 2K bytes of the 3K bytes of RAM in a Jupiter Ace is for primary for the video system (only a small amount of video system RAM can be used for general purpose use).



Mark
Now that's something I didn't know!
...me neither!!! :roll:
Mark is an infinite source of useful information! Thanks for letting us know! 8-)
dr beep
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Re: ZX80 on ZX81???

Post by dr beep »

kokkiklhs wrote: Mon May 29, 2023 1:27 pm Yes, I am aware of that (haven't tried it yet, though) but a 100% software emulator (IF such a thing is possible, I am not a programmer myself and was just wondering) would be a big programming achievement!! There could also be (in theory) e.g. a Jupiter Ace emulator for the Zeddy, AFAIK hardware-wise these machines are almost the same. Just checking the possibilities.
A software emulator would need a ZX8 ROM loaded in RAM, like SP-2-ZX80 / SP-2-ZX81.
This would also mean that a full emulator is needed.
Since the ZX81 is using most CPU time for the screen the emulator would be pooly slow.
Just to compare: SP-2-ZX81 is running on app 10% when each intrupt the screen is updated and the ZX Spectrum is updating the screen itself.
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1024MAK
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Re: ZX80 on ZX81???

Post by 1024MAK »

Sites that have information about the Jupiter Ace computer: I hope that helps ;-)

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
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kokkiklhs
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Re: ZX80 on ZX81???

Post by kokkiklhs »

@Johan: Thanks for the detailed answer, I was just wondering (and hoping)... Now I understand that even though it IS possible, it is useless...
Well, our beloved Zeddy is capable of many other impressive and unexpected things, so I won't consider that as a big disadvantage... ;)

@Mark: Wow, thank you, time for some good reading! 8-)
dr beep
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Re: ZX80 on ZX81???

Post by dr beep »

kokkiklhs wrote: Mon May 29, 2023 9:22 pm @Johan: Thanks for the detailed answer, I was just wondering (and hoping)... Now I understand that even though it IS possible, it is useless...
And you would need enough RAM 16K is not much, morelike 32K.
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