23-02-2020, 10:48 PM
(23-02-2020, 01:03 PM)someone Wrote:(16-02-2020, 07:59 PM)Ernest Wrote:(16-02-2020, 07:00 PM)someone Wrote: Here is the photo!
Hi Ernest,
Sorry for the late response because someone hasn't logged in recently and didn't subscribe to this thread.
The photo is just of an standard Alpha machine. (However it is modified with a simplistic screen flicker reduction circuit that consists of a 74LS00 placed into the "SPARE" socket and wired in. The screen flicker of a standard microbee drives someone nuts.) You're right about the coreboard having no EPROMS but if you look carefully at the bottom left of the coreboard you will notice 3 production masked ROMS.
The photo shows 3 50 way expansion boards. Which one would you like the circuit diagram? They can be concurrently plugged in if given the right 50 way cable and power supply requirements.
If you plan to build one now there'd be some component substitutions to reduce the part count and complexity.
No, the microbee in the photo is not the Alpha Plus in which the windowed environment was developed. The Alpha plus prototypes had no solder mask and contained a rat's nest of wires to counter the PCB layout mistakes and mods.
Cheers
Someone
P.S. Someone is always blamed for something!
Thanks Someone for the clarification,
I thought it would take some funky design to do it off board via the 50 way.
I agree with you on the screen flicker, have modified a number of units myself based on the deglitch circuit introduced on the later Alpha machines. I assume you are restricting the RAM writes to the video retrace period.
The resolution in my browsing was insufficient to distinguish between SRAM and Mask ROM.
I don't know the function of each of these adapter boards, but the CD card adapter has my curiosity piqued?
Now that Alpha plus prototype would have been an interesting photo.
P.S. Someone is always blamed for something! But then something is always, for someone-else to do
Best Regards Ernest
