It works!

As I recall (shyeah right... like I'mma go back and read all that!) the ordeals of the last log basically amounted to really weird luck prompting me to realize some variable initializations never occurred.

After I fixed that, it all seemed to work as-tested on a PC, up to the point of actually performing the Flash-writing, which couldn't be tested yet because the SD70 has separate chip-selects for each of its 4 16k memory-sockets, and the Flash I've been using in the first socket requires an "unlock" procedure that requires accessing 32K of its address space.

The plan since I started this flash-endeavor has been to have a jumper on "The Rominator" which selects one of two 16k pages to boot from. Simply switch the jumper to boot into the firmware-uploader, switch it back to boot into the new firmware.

I went a little overboard because, well, the simplicity of the idea grew in complexity quite quickly. 

E.G. the SD70's ROM sockets obviously don't have WriteEnable... So I need a wire and test-clip for that. 

The A14 line is pulled high, as for smaller ROMs that pin has another purpose, so I already needed/had a jumper to disconnect it and a resistor to pull the chip's A14 low... But now I need a way to actually control it (for unlocking the flash-write) AND a way to invert it (for selecting which image to boot from). OK, three jumpers. 

The Output-Enable is connected to the Chip-Enable (maybe it decreases access time?), but the flashing procedure requires /OE to be high. I ran into the same with #Vintage Z80 palmtop compy hackery (TI-86) , so if I want to use The Rominator in another project, I might benefit there, as well, from now another jumper and another test-lead. 

The Chip-Enable, now, has to have *two* inputs ORed together, and another test-lead.

Surely I'm forgetting something.

While I was at it, I decided to give A15 similar treatment as A14... Now the original "stock" firmware can be booted via jumper, as well. Oh, right, and A15 is also pulled high at the socket, so had to have a jumper and pull-down.

OK...

Now, I didn't have much space left on the board, so was quite pleased to find an SOIC 74F00 in my collection... Until I realized 100k pull-down resistors would not be anywhere near spec (600uA out of the input, 100kohm, 6V?!). Alright, well, at that point I was beat (how long has this been, a week?!) So I decided I'll just require that A14 and A15 are always driven by either an output or by power rails. A14 already has a header, now, for a test-lead, but I didn't do that for A15, so I fudged another header-pin next to the jumper for grounding.

Heh. This has gotten crazy. BUT: The previously-unnamed Rominator was of great use in #Improbable AVR -> 8088 substitution for PC/XT , and now again in this project, so I guess its new versatility could be useful in another project down the line.

(Did I mention I spent Hours fighting my printer several weeks back so I could print its schematic small-enough to strap to it? I guess I'll have to do that again. Thankfully this time I think I know why it was so difficult last time. Though, this time there's quite a bit more information to fit in there).

Oh, right... So I finally put it in the socket for the first time in what seems like forever (I seriously expected this to take an afternoon, not DAYS) and it still booted the old firmware just as I expected... But, it didn't boot all the way... What?

Took me a while to remember that ordeal of the last log... right, trying to hunt down incredible odds led me to load an earlier version. So, while flashing the latest version, I also flashed the stock firmware at 0x8000... Tried the latter first. No problemo. Tried the firmware-flasher next at 0x0000, burnt an old test-program to 0x4000 (over the serial port!). Not a hiccup. booted from that for some pithy nostalgia from who can remember how many weeks ago...

Holy Moly, I can In-System-Program, now! And I can program in C!

...only... It's been so long, I can't remember what I wanted to program...