So recently I have been playing with one of my retro toys the Sinclair QL. This is the strange beasty Sinclair built after the ZX Spectrum, 68008 CPU which is familiar(ish) to Amiga/ST owners.
So far I have a SuperHermes replacement serial/keyboard board fitted. To one machine that allows the use of PC keyboards.
Another machine has the most excellent QL-SD fitted.
Like other Retro platforms there are also new hardware manufacturers appearing like Sandy where one of the first products announced in the new SupraRAM! Waiting for my SupraRAM to use with the QL-SD!
Sandy are for a short time also offering a 40% off their replacement microdrive pads (essential as they tend to turn to dust after 30 years) with the code CRAZY40!
So as a follow on from the last post it turns out the same issue is present on the 6128 classic drive port as well. Another wire link from Pin 4 of internal connector to Pin 25 of external can be made.
Here is a picture of this mod as well.
For some reason Amstrad did not route NDSEL0 to the external drive connector so external drive accont be drive A. For me that was an issue as the internal drive on my 6128+ is broken. The fix is relatively easy and is just one wire link. You need to link the internal drive connector Pin 4 to the external drive connector Pin 9.
Here is a photo of the link which shows it in place.
So I had a rethink about the Sideways RAM and I came to the conclusion that possibly there were some timing issues causing the instability. According to this post on stardot someone had managed to piggy back a SRAM on the internal ROM without the issues I was seeing.
With this information and due to the fact I was using a 62256 (32k x 8) I figured I could actually make the cartridge without the 74HCT139 as ROMQA (Edge-A16) could be connected directly to A14 of the ram chip. /OE (Edge-A2) could be connected to /OE and /CE of the ram chip. R/W (Edge A4) could be connected directly to /WE pin of the ram chip.
The easiest way to to this was to cut the 74HCT139 completely off the board so we can use its VIAS to make the connections. I had to restore the track I had cut on Edge-A4 (Edge-A11 is still not needed). I had to make a couple of new cuts to disconnect the A14 on the ram chip from be wired to Vcc.
Anyway this is the front of the PCB from the new version.
And this is the back of the PCB where the real work with the wire links and cuts occurs.
And just to show this is all working, *ROMS command issued just after switch on.
*ROMS command issued after loading 2 roms from disk.
New welcome screen after break is pressed to initialise the new roms.
And just to check roms are executing code the *HELP +1 command that Pres rom adds.
Im pretty happy with this project now. My only regret is that Edge-B10 is not populated on the cart (as no unused pads are). If so I would have wired it to the spare socket to provide ROM 13 and not wasted a socket.
Finally I got round to taking some decent photos of my conversion of a CARE Rom Cartridge to Acorn Electron sideways RAM. This is required because for some reason Acorn decided to move the R/W pin around on the cartridge interface.
So here is the front of the PCB + mods
You can see the original PIN A11 trace has been cut to allow PIN 4 to be wire linked with it. This wire link is on the back. The wire link you see here connects what used to be pin A4 input to decoding logic to +5V to pull it always high. This used to be the master CS pin which is not present on Electron.
And here is the back of the PCB + mods.
Here you can see the pin A4 to where A11 used to enter decoding logic wire link. You can also see the trace cut that used to be the original pin A4 trace.
With these mods the Electron recognises the cartridge as sideways RAM and the Slogger *rload commands work to load roms into these slots. There is however an issue with the images getting corrupted during load. I do not know what causes this. But it has been reported as happening on other sideways RAM projects using Plus 1 cartridge slots.