Jafa E2P (Electron Second Processor) re-visit
It's been 5 years since I made the 512K E2P incorporating two User Ports, since then I have progressivly been building a smaller and more capable Electron clone. The E2P now looks huge against the size of the Electron and with the User Ports now built into the clone I thought I'd build a mini version of the 512K E2P.
To start with I removed the User Ports and reduced the component sizes by using surface mount parts where I could. With the User Ports removed I could also remove the unecessary code from the relevant GAL which in turn reduced the size of that part.
Laying out the board I placed the parts as close together as possible managing to reduce the board down to just 76mm x 89mm (3"h x 3.5"w), approximately the same size as a standard Acorn/Pres cartridge. Compared to the previous cartridge of 3.9"h x 5.5"w.
To get an idea of scale:
Lets hope it works...(two weeks later...) it did but read on..
So the board arrived and I assembled it starting this time with the surface mount semiconductors. I thought it may be a bit tricky to get the soldering iron tip to the pins if I soldered the passive components first.
It didn't take long to assemble, a couple of hours maybe and it's ready to try for the first time.
So this is where the fun begins.. I plugged it in and switched on..OK so far, the Electron powered up as expected. Doing a *ROMS and the two E2P RAM banks appeared as expected, good to get this far. Now the moment of truth.. *E2PON and I get 'can't initialise'. So what could be wrong?
My first thoughts were it could be a faulty component or I made a mistake when I coded the new GAL. As this was a prototype and using soldered on parts I gave myself the best chance off sucess by buying the surface mount components from DigiKey. I discounted all these parts from being faulty and I had also pre-tested the 74ALS14 before soldering in place so my thoughts then turned to me messing up the GAL coding.
I hadn't coded an R-S flip flop before so I thought I could test the GAL in my original E2P. With a bit of pin bending and jumper clips I installed it with the result that it worked - some good news! The problem wasn't that so I turned to the only chip left.. the 65C02P4 and yes it was faulty.
With the E2P up and running...
I left it running the opening screen of TUBE Elite for the rest of the day.
Nice and stable, so the last test was to try it in an original Electron/Plus 1..all OK.
That's another cartridge complete in the style of the clone and I think it looks quite neat in its slot - only thing I forgot was to round off the board corners, there is always something missed on the first build!
I built a second board using less IC sockets and links, now that the GAL code is proved and I know what links are needed for my Electron I could solder them directly on the PCB.
I also found a 3MHz 65C02 in my collection so I tried over-clocking it to 4MHz and it runs stable - surprised but pleased.
There is one other cartrdge I may redo to match the clone and that is the Slogger Pegasus 400 1770 disc interface..