Posted By
TLC
on 2022-11-03
09:27:51
|  Re: New Project: Hannes-compatible 256k RAM Expansion
@SukkoPera: I think I can see your points  .
Yep, the TED has no Reset' (...BTW, it has no reset similarly to the 6529B, which IMHO made that chip quite less than ideal to be used as a page register - upon reset, the expanded memory page and config remain intact, LoL  - but that's another story).
As for Csory compatibility, I wouldn't talk anyone either into or off from implementing it, I just made "my own" decision. (I'll write about that later.)
Yes, most stuffs actually support the Hannes/Solder schema. (Some years ago I checked quite a number of expanded memory specific stuffs about what schema they really supported. Unfortunately I didn't make notes about it - I was merely looking for one single true Csory memory expansion compatible stuff for testing "my" memory expansion controller prototype. All in all - I plan to repeat the test someday, and now record the results here.)
I prefer gitlab, but I also have a github account (let's discuss this later / in PM). Speaking of GAL equations, I think I already have that part ready, maybe I should share it. (Long story short - some months ago I felt inspired, and figured out that maybe I could fit the whole Hannes/Solder controlling logic, 8-bit read-writeable register included, into two 22V10 GAL's. I've already written the equations that compile successfully with galasm, but haven't tested the thing in practice, yet).
Maybe, omitting some or all unused bits from $FD16 (tying them to '1' just as you did) won't have such a big impact in practice that I presumed, who knows. (There aren't that many 256k-capable stuffs out there in the first place. Also, suppose that someone had either an enhanced, say, 512k or larger Hannes/Solder memory expansion, or, the Csory schema (whose enable bits are also in $FD16), then any legacy "256k Hannes/Solder" specific code "unprofessionally" fiddling with the unused 4 bits of the $FD16 register would already get into trouble anyway. Maybe it's indeed a legal expectation from Hannes/Solder/Csory aware programs to keep the "unused" bits "1" all the time, in which case, implementing the unused bits can indeed be omitted just as you did.)
Just for curiosity, this was my last prototype and layout below. No programmable logic chips there, they are all standard 74xx. The page register was built from a '574 and a '245 pair, with some additional controller logic. High-bits-on-reset was faked with weak pull-up resistors, plus a '74 that controlled the '574's OE' (Reset' disabled / first write to $FD16 enabled it). The register is not a full 6529B implementation, it couldn't be used as an input port (OTOH, at least it has valid Reset' ) , but it was perfect for the purpose. The prototype also already did implement the Csory expansion logic, ...minus a pair of inverters, because, I apparently got something wrong, and had to patch the thing later. All in all, the thing obviously grew a bit too large, and that was when I started to look for alternatives.
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