ALtair UIO Board?

Discuss construction, troubleshooting, and operation of the Altair 8800c computer

Re: ALtair UIO Board?

Postby AltairClone » April 6th, 2019, 10:18 am

I did a little digging into the UIO board to see how RS-232 signals end up on the DB-25 using the ribbon cable connector on the board. For the UIO, it looks like Pertec implemented the same screwed up wiring MITS recommended in the 2SIO manual: The DB-25 is wired as DCE for transmit and receive, but as DTE for the CTS and RTS signals. If a straight through DB-25 cable is used between the computer and a terminal, then the RTS output from the computer is shorted to both the RTS and DTR outputs from the terminal. These outputs are all trying to drive each other. The two CTS inputs are connected to each with nothing driving either of them.

If you want to use CTS/RTS as handshake lines, you'll have to make a custom DB-25 cable (between the computer and the terminal) that swaps CTS/RTS but does NOT swap transmit and receive. The cable should also NOT connect pin 20 (DTR) between the two DB-25's. Finally, make sure the A-B jumper on the UIO board is NOT installed.

To safely ignore CTS/RTS and DTR, cut the p7-p12 jumper on the SK-2 header and install the A-B and C-D jumpers.

Mike
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Re: ALtair UIO Board?

Postby toml_12953 » April 6th, 2019, 3:50 pm

virtualaltair wrote:
Now toml & Mike will discover 88-UIO history and save and document two 88-UIO boards.


If someone could produce a repro board with a BOM (bill of materials) of either the C700 or the UIO board,
I'd gladly sacrifice them as long as I got a copy of the bare board back! In fact a repro board with new components
could easily be more reliable than an original.
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Re: Altair UIO Board?

Postby toml_12953 » April 7th, 2019, 5:05 am

Thanks to virtualaltair, I have a UIO board!

Now I have a question (of course!)

Is the baud rate of the SIO serial port independent of the ACR cassette baud rate?

Right now the board is strapped for 2400 baud but cassettes need 300 baud. Do I need to
change the SIO baud jumper? I wish I could find a UIO manual! I only have a 17-page setup
guide which is great for jumper settings but short on explanation.
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Re: ALtair UIO Board?

Postby AltairClone » April 7th, 2019, 8:07 am

In the “ACR Operation” section on page 1 of the guide you have it states the ACR is 300 baud only (I.e., there are no switches or jumpers to change it).

In the “SIO Operation” section on page 3 it shows that the SIO baud rate is selectable via the SK1 header.

Seems pretty clear to me: The ACR is fixed at 300 baud, the SIO baud rate is strap selectable via SK1.

Mike
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Re: ALtair UIO Board?

Postby AltairClone » April 13th, 2019, 1:32 pm

I’m glad you guys have pushed the UIO board to the forefront here recently. Because of you, I have pulled out my UIO board and now have both the 2SIO port and the ACR functions working reliably. It’s a cool board and very clean compared to the original ACR design.

And now, with test equipment out for working on the UIO, I’m going to get an original ACR board I’ve had sitting around for four years up and running.

Mike
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Re: ALtair UIO Board?

Postby toml_12953 » April 14th, 2019, 10:00 pm

AltairClone wrote:I’m glad you guys have pushed the UIO board to the forefront here recently. Because of you, I have pulled out my UIO board and now have both the 2SIO port and the ACR functions working reliably. It’s a cool board and very clean compared to the original ACR design.

And now, with test equipment out for working on the UIO, I’m going to get an original ACR board I’ve had sitting around for four years up and running.

Mike


You have become One of Us™

When I first installed mine, I tried the serial port. Worked perfectly. Tried writing out data. I could hear it on the tape just fine.
Tried reading in data. Nothing. Arrgh! I adjusted the trim pot all over the place and ran the test programs and no data at all. Phooey!
I looked closely at the jacks on the back of the computer. Aha! one wire had broken off the lug when I mounted the jack. I resoldered it
and WOOT! My test tape that writes out 125 octal continuously was reading back in and displaying 01010101 (octal 125) on the data lights
with just a few glitches. A quick adjustment of the trim pot eliminated those and now I have a solid 125 showing. CSAVE and CLOAD work great
and I can use the machine the way it was used in 1975. I have created tapes from all the tape images of Altair BASIC available and so I can
load BASIC the old-fashioned way. If anyone thinks I'm giving up my floppies for this, though, they're crazy! :)

I have noticed the serial port is a 2SIO-type and not the older SIO. That's good for me. I can now use five terminals in TS BASIC. Why? Because I can!
The UIO is so much more reliable than the old ACR two-board set and it's much easier to adjust. The older ACR was finicky even on good days. With the UIO
you have to deliberately try to make it fail.
Also with the old ACR, If you added or removed any boards, you'd usually change the timing of the system enough to require a re-calibration!
Fugeddaboudit as we say in New York.

To anyone who doesn't already have one: If you see one available, GET IT!

Tom L
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