Re: Memotech HRG: ROM mirroring!
Posted: Fri Feb 23, 2018 4:14 pm
@sirmorris
Thanks a lot.
@Siggi
Never read the fucking French manual !!!
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Memotech HRG: ROM mirroring!
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Re: Memotech HRG: ROM mirroring!
Posted: Fri Feb 23, 2018 5:21 pm
Re: Memotech HRG: ROM mirroring!
Posted: Fri Feb 23, 2018 6:35 pm
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 effectsirmorris 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.
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
Re: Memotech HRG: ROM mirroring!
Posted: Fri Feb 23, 2018 7:11 pm
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?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..
He switches to 32k location for writing and back to 0k for shadow ROM.
http://www.user.dccnet.com/wrigter/inde ... XRAMIO.htm
Re: Memotech HRG: ROM mirroring!
Posted: Sat Feb 24, 2018 12:57 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.Andy Rea wrote: ↑Fri Feb 23, 2018 6:35 pmThis 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 effectsirmorris 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.
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
Re: Memotech HRG: ROM mirroring!
Posted: 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.
On the second release, the Basic Rom stay in the ZX81's case, but...
We need to reconstruct the ULA signal, to drive the in-board cartridge signal.
Electronic scheme: (UDG@h2000 / IR=h20xx)
http://zx81.ordi5.free.fr/vtr/download/ ... ECO%5D.pdf
To use the UDG, you had to export the Basic ROM on the extension bus.
Like the cartridge player, cf. Mageco.
On the second release, the Basic Rom stay in the ZX81's case, but...
We need to reconstruct the ULA signal, to drive the in-board cartridge signal.
http://zx81.ordi5.free.fr/vtr/download/ ... ECO%5D.pdf
Re: Memotech HRG: ROM mirroring!
Posted: Sat Feb 24, 2018 4:18 pm
In the 0-8K range? With a new chip select memory decoder for internal ROM RAM using techniques like Wilfs? Forcing ROMCS low?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.
Re: Memotech HRG: ROM mirroring!
Posted: Sat Feb 24, 2018 4:29 pm
Yes, Gammaray !
It in the 0-8k memory room...