TTY 33 Not working with Clone

General discussions related to the Altair 8800 Clone

TTY 33 Not working with Clone

Postby toml_12953 » February 16th, 2014, 10:47 pm

I'm trying to hook up my TTY ASR-33 to the clone and it doesn't print anything (lights on the clone flicker when I press return, though). I can hook the clone to both a PC using TeraTerm and an ADM-3A and it works with them fine at the same 110 baud the TTY uses so I know the clone is doing its part. I can use the TTY with my PC using TeraTerm, the Altair32 emulator and a Wang 3300 emulator. It works fine with those so I know the TTY is working. I'm stumped. Any ideas?

TIA

Tom L
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Re: TTY 33 Not working with Clone

Postby AltairClone » February 16th, 2014, 10:59 pm

If you use your TTY with your PC, then you obviously have a current loop to RS232 converter in place and your TTY is wired as DCE (since PCs are wired as DTE). This leaves both the TTY and the Clone wired as DCE. Of course, you haven't told me about the cables and connectors used in your tests to hook between these various devices, so I may still be wrong here, but it sounds like all you need to do is swap 2 and 3 in the cable between the Altair and the TTY.

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Re: TTY 33 Not working with Clone

Postby toml_12953 » February 17th, 2014, 8:18 pm

it sounds like all you need to do is swap 2 and 3 in the cable between the Altair and the TTY


That's the job of a null modem, right? I tried it both with and without a null modem adapter. With the null modem, I can send data TO the Altair but nothing is received FROM the Altair. Without the null modem, no data flows either way.
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Re: TTY 33 Not working with Clone

Postby AltairClone » February 17th, 2014, 10:08 pm

So yes, the null modem in-line is correct. Sounds like your RS232 to current loop adapter may need more current or a higher voltage than the Clone is outputting. What are you using for a current loop adapter?
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Re: TTY 33 Not working with Clone

Postby toml_12953 » February 18th, 2014, 3:55 am

I use a 232CL9R from B&B Electronics. I'm using an active loop for one of the loops. Maybe I should try a second power supply for the side that receives from the Altair?

Another observation is that the real Altair's 2-SIO board works with this converter with no problem. Is there a possibility that the clone's serial port isn't 100% compatible with the original?

From the Website:

"High speed optical isolators couple and isolate transmit and receive data. All B&B Electronics current loop converters have a transmit (T+ and T-) and a receive (R+ and R-) loop. Each loop may be operated as an active or passive loop. When the converter needs to provide the loop current, a 12 VDC power supply is required for the current loop side. Maximum baud rate recommended for current loop converters is 19.2 kbps.

Models 232CL9R and 232CL4R are port powered RS-232 to current loop converters. No external power required for passive loop installations. A power supply is required to generate an active loop."
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Re: TTY 33 Not working with Clone

Postby AltairClone » February 18th, 2014, 12:26 pm

Both the send and receive loops in the Teletype are passive, so I imagine you presently have a single 12 volt power supply that is connected to the 232CL9R in the proper manner to power both loops. Only a single power supply is required to supply both loops.

Another option with the 232CL9R is whether the internal 5v logic supply is generated from the RS232 input signals or from an external 12 volt supply. Based on your symptoms, I'd guess that presently, your board is wired to generate 5v from the RS232 signals as opposed to generating 5v from the external 12v supply. The Clone's RS232 output is RS232 compliant, but only swings +/-4 volts or so. Because of this lower voltage swing, it could be the internal 5v required by the 232CL9R is not being generated properly.

I'd check/modify the power connections to the 232CL9R so that the 12v external supply powers both loops and also powers the 5v internal supply. That should fix the problems you are having. Let me know what you find!

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Re: TTY 33 Not working with Clone

Postby toml_12953 » February 19th, 2014, 8:12 pm

AltairClone wrote:I'd check/modify the power connections to the 232CL9R so that the 12v external supply powers both loops and also powers the 5v internal supply. That should fix the problems you are having. Let me know what you find!

Mike


Success! If the RS-232 port doesn't supply enough power, a *second* 12V supply must be connected to the 232CL9R. The first supply powers both the Tx and Rx loops and the second powers the RS-232. It's ugly but it works. Thank you for your time and patience. Now I'm off to play *er* I mean WORK with the Altair.

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Re: TTY 33 Not working with Clone

Postby AltairClone » February 19th, 2014, 8:57 pm

Great! If you want another project, here's a very simple 20ma to RS232 interface that easily fits inside the Teletype: http://altairclone.com/teletype.htm

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Re: TTY 33 Not working with Clone

Postby AltairClone » February 20th, 2014, 4:56 pm

On the B&B converter, you can actually use the same power supply for both of the loops and the RS232 logic, however, you have then lost isolation between the Teletype and the computer you are interfacing to.

Both the Altair SIO and 2SIO boards interfaced to the Teletype without isolation. The interface board I built also connects to the Teletype without isolation. The send side from the Teletype (keyboard, reader, answer-back) is a completely passive path not referenced to anything. Power and components in the receive side of the Teletype (UCC-6) are isolated from the A/C mains via a transformer and the minus side of the 20ma input is then referenced (I think) to chassis ground. If not, then the minus side of your circuit establishes the voltage reference of the Teletype's minus input. I've seen both in the drawings. I'll think now I'll check my Teletype and find out for sure!

Then again, if you have it working and there is no smoke, why mess with it!?

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Re: TTY 33 Not working with Clone

Postby AltairClone » February 21st, 2014, 11:19 am

To follow up on my previous post, I checked my Teletype (UCC-6 Call Control Unit) and the minus side of the receive loop (transmit from PC) is connected to Teletype chassis ground when the Line/Local knob is in the Line position. The Teletype chassis ground is connected to earth ground.

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