Reproduction Altair 88-UIO Universal I/O Board

[toml_12953]

Attempt to upload Excel BOM for 88-UIO board.

It looks like some have fallen out of stock. It's a constant battle for us vintage computer enthusiasts.

Yes, it certainly is! At least Digi-Key will ship the parts when they do come in.
I ordered the out-of-stock parts on eBay, though, since I'm notoriously impatient!

Good news! DigiKey has shipped all the back ordered parts so if you order now, you'll get the entire DigiKey portion of the BOM at once.

[tep392]

Please post a picture of your board when you have it finished. :)

[tep392]

I should post a note about configuring the jumper block for the serial interface. Mike has posted some notes here that explains its quirks.

https://deramp.com/downloads/altair/hardware/88-UIO/

I chose the route of configuring the port as a DTE and then using a standard cable plus null modem adapter to my PC.

[Neukam]

Here is my assembled board. I apologize for the less than pristine appearance. I'm need to change the IPA in my wash tank to get the rest of the residue off. Waiting on more IPA...

The board is tested and seems to work well. I had to change the resistor value for the SW-1-4 modification. 2K7 was a bit too stiff. 3K3 worked perfectly. I get 50% +-0.3% duty cycle without adjusting the pot when changing modes.

The lifted pin on E1 and the small bodge wire on the back set the address of the SIO port to 14h.

Has anyone tried to mod the cassette interface for 1200 baud?

[Neukam]

I've been experimenting with changing the baud rate of the cassette interface. I haven't had any success with 1200 baud, and I get some strange behavior that I don't understand. I might be able to get 1200 baud working if I double the audio frequencies to 4800/2400. I have been able to get 600 baud working, however, and it seems to work reliably :)

[tep392]

The board looks great! Congrats on the successful build!

Regarding 1200 baud, I don't think the PLL has enough time to lock at that rate. It takes roughly 1.2ms to lock. It's worth a try to double the modulation frequency. There might be some tuning of the PLL components needed to get a quicker lock. Here's a pic of the KC frequencies and the PLL lock at 300 baud.