Memotech HRG: ROM mirroring!

Discussions about Sinclair ZX80 and ZX81 Hardware
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siggi
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Re: Memotech HRG: ROM mirroring!

Post by siggi » Fri Feb 23, 2018 4:14 pm

XavSnap wrote:
Fri Feb 23, 2018 2:29 am

Note: Not easy to type-in a program in French!!!
:lol:
And it's also not easy to write a program in C# (for a customer in France), when the documentation is also written in French :roll:

Siggi :mrgreen:
My ZX81 web-server: online since 2007
http://zx81-siggi.endoftheinternet.org/index.html

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XavSnap
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Re: Memotech HRG: ROM mirroring!

Post by XavSnap » Fri Feb 23, 2018 5:21 pm

@sirmorris
Thanks a lot.

@Siggi
Never read the fucking French manual !!!

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Andy Rea
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Re: Memotech HRG: ROM mirroring!

Post by Andy Rea » Fri Feb 23, 2018 6:35 pm

sirmorris wrote:
Fri Feb 23, 2018 3:21 pm


Under normal circumstances you cannot replace the ROM at 0000-0fff with the shadow RAM because the I register needs to be set to $1E in order for the character generator to work. If you change I register then the characters on screen will be messed up, psuedo hires.

This using the lower bit of the I register is a cool trick, remember the low bit isn't used under normal conditions $1E can be $1F with no ill effect

so this is pretty cool idea and maybe could be extended to cover the entire 8K range to allow for complete customized rom that you can load in from your favorite storage device...

regards Andy
6 x ZX81, 1 x TS1500 , 1 x +3e, 1 x timex 2040 printer, 1 x timex 2020 cassette deck, siclair printer and some spectrum

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gammaray
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Re: Memotech HRG: ROM mirroring!

Post by gammaray » Fri Feb 23, 2018 7:11 pm

All Pokes are sent to the buffer... how replace the main rom.
The HRG Rom is located at &2000, and can't be the buffer Ram // or // the poked byte is redirect in a ram at the same location..
Does Wilf Rigter's article on memory have any indication bearing on how this could be done with switching of ram location using (instead of being victim to ) ghosting feature of RAM/ROM chip select?

He switches to 32k location for writing and back to 0k for shadow ROM.

http://www.user.dccnet.com/wrigter/inde ... XRAMIO.htm
memory decoder_2018-02-23_12-10-50.png
Yes I may be off in left field...
Finish what you start. Truth is over the mountaintop or six feet under.
4 x TS1000, 2 x TS1500 , 2 x timex 2040 printer, 1/2 x timex 2020 cassette deck, ZXPAND+AY, ZeddyNET, ZXBlast..., unfinished Spectrum...Still no life!

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mrtinb
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Re: Memotech HRG: ROM mirroring!

Post by mrtinb » Sat Feb 24, 2018 12:57 pm

Andy Rea wrote:
Fri Feb 23, 2018 6:35 pm
sirmorris wrote:
Fri Feb 23, 2018 3:21 pm
Under normal circumstances you cannot replace the ROM at 0000-0fff with the shadow RAM because the I register needs to be set to $1E in order for the character generator to work. If you change I register then the characters on screen will be messed up, psuedo hires.
This using the lower bit of the I register is a cool trick, remember the low bit isn't used under normal conditions $1E can be $1F with no ill effect

so this is pretty cool idea and maybe could be extended to cover the entire 8K range to allow for complete customized rom that you can load in from your favorite storage device...

regards Andy
I assume this will only work when the Memotech HRG is connected. Otherwise it would be cool to use the internal 1k for ROM customization.
Martin
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube

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XavSnap
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Re: Memotech HRG: ROM mirroring!

Post by XavSnap » Sat Feb 24, 2018 4:14 pm

Hi,
To use the UDG, you had to export the Basic ROM on the extension bus.
Like the cartridge player, cf. Mageco.
Image

On the second release, the Basic Rom stay in the ZX81's case, but...
Image
We need to reconstruct the ULA signal, to drive the in-board cartridge signal.
UDG_trav.JPG
Electronic scheme: (UDG@h2000 / IR=h20xx)
http://zx81.ordi5.free.fr/vtr/download/ ... ECO%5D.pdf
:mrgreen:
Last edited by XavSnap on Sat Feb 24, 2018 4:27 pm, edited 2 times in total.

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gammaray
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Re: Memotech HRG: ROM mirroring!

Post by gammaray » Sat Feb 24, 2018 4:18 pm

I assume this will only work when the Memotech HRG is connected. Otherwise it would be cool to use the internal 1k for ROM customization.
In the 0-8K range? With a new chip select memory decoder for internal ROM RAM using techniques like Wilfs? Forcing ROMCS low?
Finish what you start. Truth is over the mountaintop or six feet under.
4 x TS1000, 2 x TS1500 , 2 x timex 2040 printer, 1/2 x timex 2020 cassette deck, ZXPAND+AY, ZeddyNET, ZXBlast..., unfinished Spectrum...Still no life!

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XavSnap
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Re: Memotech HRG: ROM mirroring!

Post by XavSnap » Sat Feb 24, 2018 4:29 pm

:ugeek:

Yes, Gammaray !
It in the 0-8k memory room...

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