SD81 Booster

Discussions about Sinclair ZX80 and ZX81 Hardware
billloguidice
Posts: 4
Joined: Thu Jul 06, 2023 2:52 pm

Re: SD81 Booster

Post by billloguidice »

wilco2009 wrote: Wed Aug 30, 2023 3:51 pm I remind you that to prepare the SD you have to copy the content of the "SD CONTENT" folder that is in the GIT in the root of the SD.
Can you kindly provide a link to that? (or one level above?)
wilco2009
Posts: 74
Joined: Sat Feb 04, 2017 12:03 pm

Re: SD81 Booster

Post by wilco2009 »

billloguidice wrote: Wed Aug 30, 2023 4:13 pm
wilco2009 wrote: Wed Aug 30, 2023 3:51 pm I remind you that to prepare the SD you have to copy the content of the "SD CONTENT" folder that is in the GIT in the root of the SD.
Can you kindly provide a link to that? (or one level above?)
https://codeberg.org/Retrostuff/SD81-Bo ... %20Content
wilco2009
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Joined: Sat Feb 04, 2017 12:03 pm

Re: SD81 Booster

Post by wilco2009 »

The first 6 interfaces with case shipped.

:)
wilco2009
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Re: SD81 Booster

Post by wilco2009 »

I publish in the first post the list of tested programs. Above all I am trying the HiRes and PseudoHiRes, because the normal ones, in principle, all work.
I'm updating the list.
We are investigating why some PseudoHiRes programs do not work.
As soon as we find a solution we will publish the corresponding firmware update.
wilco2009
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Re: SD81 Booster

Post by wilco2009 »

Well, I have already found out why the few Hires programs that do not work fail.
I will post here an update of the CPLD and instructions for downloading it and loading the programs later.
wilco2009
Posts: 74
Joined: Sat Feb 04, 2017 12:03 pm

Re: SD81 Booster

Post by wilco2009 »

I'll explain you the background of the few games that didn't work:
The SD81Booster is an interface that completely replaces the ROM and internal RAM of the ZX81 with a RAM chip, existing in the interface, that performs both functions.
This allows, for example, to be able to hot load the Forth ROM that exists for the zx81 from the SD, or replace the character set with another.
On the other hand, the ZX81 ROM circuit is perhaps the most complex part of the machine, and has two parts:
- the part in which the instructions are executed, which is managed like any other ROM, activating the ROM when the address being executed is below the first 8KB
- the character generation part for display, which in the case of the ZX80 and ZX81 is carried out during the REFRESH phase of the processor.
As I already said, the circuitry to control all this is replicated within the CPLD of the interface.
The games that did not work belonged to the category of games with pseudo-hires, which is not Hi-res in the strict sense, but continues to use text mode, but the pointer that indicates where the character table is in ROM is changed for each horizontal line of pixels.
It seems that this is managed in a slightly different way between some games and others, so, with the interface circuitry, there are some pseudo-hired games that work (for example Manic Miner) and others that apparently are giving some kind of problem. (like Against The Elements).
At the moment the solution we have implemented is a means of telling the CPLD to use the internal character generation circuitry in cases of interest to us. This will require doing a POKE prior to loading the program to give the appropriate instructions to the CPLD.
It's just a temporary patch until we find the definitive solution.

How to update the CPLD:

- Copy the file SD81CPLD.XSVF to the root of the SD, insert the card and power up the zx81
- The status LED will begin to flash warning that the CPLD is going to begin programming for a few seconds, warning that we must not remove power from the equipment until the end of the process.
- After about 5 seconds it will start with a slower flashing that will progressively change the color of the LED from red to green.
- When the process is finished, the LED will remain solid green, after which we can do a reset so that it starts normally. (on the SD the file that we have copied will have been renamed to SD81CPLD.DONE)

How to load problematic games:

POKE 4096,1
LOAD FAST "<FILENAME>"

With POKE 4096,0 (or after a power cycle) we will return to normal operating mode.

Note that the POKE will not actually write to the ROM, but with this "attempt" the CPLD will know that it will have to change operating modes.

The effect lasts until the next on/off cycle, so it will remain even if a RESET is performed from the interface.

File to save the CPLD:
https://codeberg.org/Retrostuff/SD81-Bo ... er/V2/CPLD
wilco2009
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Joined: Sat Feb 04, 2017 12:03 pm

Re: SD81 Booster

Post by wilco2009 »

Next bacth ready to be sent. :)

Image

In some days, update for compatibility with H.E.R.O......
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Paul
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Location: Germanys west end

Re: SD81 Booster

Post by Paul »

Do you have a modified version for use with SD81 of the BigBang ROM as well?
https://www.sinclairzxworld.com/viewtop ... f=5&t=2986
In theory, there is no difference between theory and practice. But, in practice, there is.
billloguidice
Posts: 4
Joined: Thu Jul 06, 2023 2:52 pm

Re: SD81 Booster

Post by billloguidice »

I received mine here in the US. I haven't had a chance to try it yet.
wilco2009
Posts: 74
Joined: Sat Feb 04, 2017 12:03 pm

Re: SD81 Booster

Post by wilco2009 »

Paul wrote: Fri Sep 08, 2023 10:55 am Do you have a modified version for use with SD81 of the BigBang ROM as well?
https://www.sinclairzxworld.com/viewtop ... f=5&t=2986
I have not tested yet with this ROM, but in theory it is possible to test BigBang ROM just using LOAD FAST "zx81x2.rom". It will load the ROM an will reset the system with the new ROM.
Unfortunatelly this ROM has not extensions to use the SD.
It could change in the future if I contact with the BigBang ROM author.
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