The SPLYNX Modifications

[Womble]

Someone in the forum was asking about the Splynx modifications.

A picture is worth a thousand words.

I cannot remember what issue it fixed, it was some interrupt timing issue I think.

There are modifications upto level 4 in the Lynx 48/96 PCB, these may include this fix I have not checked.

Lynx to Splynx ModsSmall.jpg (354.51 KiB) Visto 332 veces

A larger version can be found here

http://www.retrogubbins.co.uk/downloads ... ifications

[kokkiklhs]

Oh, thank you, Pete! I am the one who was asking and btw, I recently thought of opening this very thread to ask you some details about it... But you came first, seems that you've read my mind!!


Cheers

[kokkiklhs]

Oh, there's also a 40/80 columns mod (!!!) as well, I wasn't aware that the Lynx can display 80 columns... Such a bizarre but also interesting and underrated machine...

Well (question goes mainly to Pete), are the HW Splynx mods necessary to any Lynx 48/96 board in order to run converted ZX Spectrum software? This is a point that I haven't understood yet...

Another (rather silly) question: Does CP/M run only on 128k machine? I understand that the 128 has a different architecture and an upgrade of 48/96 to 128 is not possible (at least without major hardware hacking), but how about e.g. the 96? Isn't CP/M supposed to run on any machine with a Z80 and a minimum of 64k free RAM?
Please excuse my naivity here, but I'm completely noob to Lynx (though more or less experienced with other 8bitters)...

[Womble]

>>>Oh, there's also a 40/80 columns mod (!!!) as well, I wasn't aware that the Lynx can display 80 columns... Such a bizarre but also interesting and underrated machine...

I haven't tried that mod, I think there will be some software POKEs to go with it to change the 6845 registers.

>>>>Well (question goes mainly to Pete), are the HW Splynx mods necessary to any Lynx 48/96 board in order to run converted ZX Spectrum software? This is a point that I haven't understood yet...

I think it depends upon the board revision, later boards don't need the mod. I have an Issue 4 board which runs them fine.

I will check the mods schemas.

>>>>Another (rather silly) question: Does CP/M run only on 128k machine? I understand that the 128 has a different architecture and an upgrade of 48/96 to 128 is not possible (at least without major hardware hacking), but how about e.g. the 96? Isn't CP/M supposed to run on any machine with a Z80 and a minimum of 64k free RAM?
Please excuse my naivity here, but I'm completely noob to Lynx (though more or less experienced with other 8bitters)...


There was indeed a mod to make CPM run on the 96 with 80 col mod.

I think I have the disks somewhere.

[ron]

I had read that the Lynx 96 supported an 80 column mode, what do we know about this?

[Womble]

I've seen a couple of 96K 80 column mods:

1. Upgrading the RAM on the daughter card

2. Using Green+Alt green

I will dig out some information.

[Womble]

I've spent the day in my forest looking over the various circuit diagrams I have.

There are a few errors I can spot even in the original schematics from Camputers.

The one I posted above of the Splynx mods has a couple of errors.

The diagram comes from Martyn Smith who passed away some years ago.

Looking at the diagram aside the description of the mods from Phoenix (see below)

The output of M1 on the Z80 is connected to IC57 pin 9, this is shown on the diagram the wrong way round, pin 9 on a 7404 is the input to the inverter.

The diagram also shows a connection between the output of one of the NAND gates in IC28 and the inputs 1,2 of another NAND in IC28 which is where we are connecting /IOREQ and /M1

It would seem to me that the connection between the 1st NAND and the inputs of the 2nd must be broken howver this is not described in the Splynx modification.

SplynxModsDescriptionSmall.jpg (120.74 KiB) Visto 222 veces

[Kyp]

Is there some kind of explanation about that SPLYNX modifications? Something more like a 'theory of operation' than some schematics mods. It would be great if I can add this modifications to my FPGA core.

[Womble]

Hi kyp,

The only explanation I have is in the doc above 'faulty interrupt hardware'

The actual mod seems to be synchronising M1 and IOREQ as the enable on the bank switch and main address demux chips.

Its possible this wasn't needed on later boards. There is another document which shows IC47 being 'modded' direct from the factory.

https://github.com/ukscone/Camputers-Ly ... 300dpi.png

https://github.com/ukscone/Camputers-Ly ... 300dpi.png

[Kyp]

I think I was confusing the splynx mod with the 80 column mod. Any information about that 80 column mod? BTW, I don't think there are problems with interruptions in the FPGA implementation, there are no multiplexer chips, memory subsystem is completely different.

[kokkiklhs]

I've spent the day in my forest looking over the various circuit diagrams I have.
.....
Looking at the diagram aside the description of the mods from Phoenix (see below)

Thank you so much for investigating on behalf of all of us... An yes, at last, the Phoenixx modification sheet with STEP 4 visible, even though it doesn't say much, it was a big mystery for all these years...!!!

[jltursan]

Indeed, the missing "step 4" at least!, it doesn't adds anything tho

Maybe looking for the patched ZX games (by Tim Titchmarsh) and what's the difference with the originals we can get a functional idea of what's happening with the mod...

[Womble]

A few years ago I started out doing this, I tried to match up sections of JSW with the Lynx version.

For example - does the Spectrum code run and build up the usual display file in an area of memory - and then that gets transferred by some interrupt trickery into the bank structure of the lynx?

Or is the zx code heavily modded each screen write to call a 'zx->lynx' conversion and write.

I think I remember a display file being built up when I play chequered flag for example in Pale - in bank 1 ram

[Womble]

Running KnightLore in PaleSDL shows 3 different display files in Bank 1 at 2000 4000 and ?D000

PSDLknight.png (173.59 KiB) Visto 193 veces

or is this a usual double buffer technique the game uses?

It is the same in Alien8


Delta Wing is slightly different using 2000 4000 and 7000

PSDLdeltawing.png (183.95 KiB) Visto 193 veces

The Hobbit only has two display files at 2000 and 4000

PSDLhobbit.png

(194.42 KiB) No descargado aún

[jltursan]

The Lynx banking scheme is a real nightmare

Both $2000 and $4000 are the 8KB RAM segments available in a 48KB but they're not enough to buffer a complete screen; so I can't imagine how is it managing the ZX screen layout. I don't remember how the 96KB has its memory banked

[Kyp]

The Lynx banking scheme is a real nightmare
I don't remember how the 96KB has its memory banked

It has the same four banks ROM/User RAM/Video RAM/Extra ROM than the 48K but user RAM is 64K instead of 8K, and ROM is 24K (3x8K) instead of 16K (2x8K)