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Each terminal on port B has a 270 ohm resistor in series with the PIC’s pin.

Yes, that’s the same stack that’s in the XCMD download.

First signs of life! This is just a simple test, I’m reading the ID jumpers and outputting their values on port B (no ADB code in play at all), but it helped me sort out the PIC’s config words. I didn’t know that low voltage programming mode steals RB3, which is one of the unit ID pins. I also...

I still need to pull an image of my ADB I/O disk, but the floppy didn’t contain anything particularly special. I think it had the HyperCard stack and maybe the AppleScript extensions. It was just a physically shippable version of stage same stuff available on the website.

Oh, I guess I should pay closer attention to the manual! I don't remember any software using that functionality. If I'm not mistaken, for something to take advantage of the SRQ functionality, it would need to be implemented as a driver, rather than a "user space" program, and I can't think of...

The protocol only has room for 4 bit addresses, or 16 devices. The toolbox code uses 8 bit values for the addresses, but the underlying protocol only has room for 4 bits of address.

I suspect the ADB I/O as we know it was carved out of a more complex device, one with more inputs and outputs. The protocol feels like it's unnecessarily verbose for a device with 8 I/O pins. I batted around the idea of using the extra bits in the protocol to make a bigger device, but the...

I haven't seen anything in the ADB manager that hints at it supporting more than one host controllers; all of the functions are structured around there being a single linear address space. But I was thinking, all of the ADB I/O commands include the two bit unit ID in the command, and they don't...

Now I just need to find a working old mac…

Last year I was down a different ADHD rabbit hole and I was reverse engineering Trimble GPS receivers! Software: I have an original floppy somewhere... I should look for it. The wayback machine appears to be struggling tonight, so I can't re-download the files, but when I did a couple weeks...

Oh, and here’s the original unit (left) and the reboot (right). I’m switching mine to black screw terminals tomorrow to complete the “dark mode” look.

And now, story time. In 1997, 16 year old me I learned about the ADB I/O, I think from and ad in a magazine. It was expensive, and I had no money, so I put it on my christmas wishlist. Well my parents delivered, and on christmas morning, I gleefully opened the box of my first ADB I/O. The...

PCB and entirely untested firmware here: http://code.beefchicken.com/adbio

Oh my this is hilarious. Guess what I’ve been up to? I just finished the firmware tonight. My board is a clone of the original, it even fits the original case. I’m friends with the purveyor of the original; sadly the source code for the PIC16C71 was lost… but now there are two versions! I...