The purpose of the HDD Synth Prototype MKII was to create the card fully working, other than the ISA based IDE activity detection.
It's very easy to bite off more than you can chew and by trying to do everything in my first iteration, I'd certainly done just
Now that the MKII is effectively complete, I've been starting to breadboard the approach to detect IDE activity without needing a direct connection to the PCs HDD LED
I've decided to achieve this with an electronics based approach, rather than using the Pi Pico in software.
This is achieved by having a pair of 74HC573 latch chips, that attach to the ISA address bus and then "latch" an address when they receive a high signal from the ISA BALE line.
This freezes that address so that the ATF22V10C CPLD (Complex Programmable Logic Device) can then see if the address on the bus is within the primary IDE range (1F0h - 1F7h) whilst also checking the status of the ISA IOR, IOW and AEN lines.
We we're detecting the correct activity within the correct range, that should mean HDD activity
The CPLD allows me to essentially bake in all that logic into a chip that can run at the speed of the ISA bus.
I used WinCUPL to write that logic which it turns into a JEDEC file. In turn this is loaded by the XGecu software for my T48 chip programmer.
Easy, right!?
Even with the CPLD "simplifying" the wiring, it's still a real rats nest of wires to connect all the chips together. One wrong wire and it won't work! Of course that's not frustrating...
So after I'd put everything together I attempted to plug it into my PC and... it didn't work, of course
Thus followed a few hours of testing each of the parts of the circuitry in isolation to determine the fault(s)
I did make a mistake on my RC envelope which mean the LED would never light up, so I corrected that issue
However the rest of the circuit seems to be working correctly.
I've ordered some shorter jumper wires, as the ones connecting my debug ISA card to my breadboard are far too long to safely transport the high speed ISA signals.
Now I've just got to wait for the Royal Mail to deliver them. This could take some time...
