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"sd70 keyboard" schematic

A project log for Z80 Reverse-Engineering And Hacking Adventures

What else can I say?

eric-hertzEric Hertz 06/20/2022 at 03:143 Comments

Anything of particular note? Hmm... Definitely etched "in-house." I keep thinking its crazy there's such tiny power/ground traces, and that they meander like they do, but the vast majority of the board doesn't use them.

Working my way back into the motherboard, next, from here... That'll likely take longer, since the friggin traces jump sides so often...

Updated Keymatrix. Thankya to @ziggurat29 

Note that Col3/row3 has no button, nor a place for one, but @ziggurat29 says there's code for it(?!). I don't see any hidden buttons/pads on the keyboard nor mainboard. Though I haven't hunted those traces on the mainboard.

Oh Snap, I forgot to make note of the fact most each button has two names, which the "2nd" button selects. If I understand correctly.

....

These be the LEDs. If you don't care too much about the wiring, the 8255 on the right is where to look. The labels mostly correspond with the button names. Although four LEDs are not associated with buttons. "Pause" and "Stop" are the easy ones. "Slew" and "Scan" are both button-names and independent LEDs. So, I called the independent LEDs e.g. "Slew Active" and the ones on the buttons "Slew BTN"

They're driven at their cathodes through 74LS245's on the mainboard, we're guessing for drive-strength, but 245's don't invert, so in code I'm pretty sure, they're also active-low. The 245's DIR and OE pins are tied active.

There seem to be potential for two more LEDs which are N/C at the "keyboard" PCB. Again maybe suggesting the mainboard was intended to be used in other systems.

8255 cleaned-up, and in its entirety:


Discussions

ziggurat29 wrote 06/21/2022 at 13:12 point

fabulous. I'll propagate the LED work into the listing. I already have accommodated the 2nd function key names in there, so don't sweat it on the diagrams.

Since we don't know about the mysterious AMD device, and don't have GPIB populated, we are on the cusp of being able to make some new firmware. So put on your product manager hat; lol.

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Eric Hertz wrote 06/22/2022 at 05:34 point

Hah! Sounds exciting! I'd better get my ROM-programming plan-of-action figured out, quick-like!

BTW, we're planning to work within stock-hardware limitations, first (E.G. 2K of RAM), yeah? That'd probably get things moving sooner, at this end.

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ziggurat29 wrote 06/22/2022 at 12:13 point

Yes, I think for board bring-up, we can just use the 2K and only worry about programming a 27128. After we get the drivers working like we want, we (well, you) can think about subsequent expansion.

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