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Moonferret
June 23rd, 2016, 05:31 AM
Hi Folks!

I've recently got my model 33 Teletype up and running and have connected it to my KIM-1. It's mostly working, I can enter & run code fine, even punch out data to paper tape. However, I can't seem to get it to read programs back in from paper tape. The reader on the teletype just won't start when online.

The Teletype is fitted with the 'Reader Run Relay' so that the host can start / stop the reader but I have been unable to find any documentation of how to wire this up to the KIM or even bypass it. Does anybody have any suggestions? TIA

Cheers,
Dave

daver2
June 23rd, 2016, 01:04 PM
Hi Dave,

I don't think the KIM-1 will drive the equivalent of the "reader run relay" as standard from the monitor. You would have to use the 'user' parallel port, develop a small digital one-bit interface box to the teletype and write a bit of software to operate the relay. Too much trouble IMHO...

As to why the reader won't work manually - now that's another issue... I'll have a look at the schematics for the Model 33 tomorrow.

Dave

billdeg
June 24th, 2016, 06:08 AM
can you post photos and voltage readings? I blew out my Kim's circuits related to TTY when I attempted it, not yet repaired. You can either bypass or remove the reader relay entirely depending if you need it for something else. You really only need the reader run relay for DEC and mini stuff asaik

NeXT
June 24th, 2016, 08:11 AM
Doesn't the reader operate by the XON/XOFF (CTRL+Q/CTRL+S) while set to AUTO or was that another option?

daver2
June 24th, 2016, 10:29 AM
There seems to be a bit of confusion here with the documentation...

I assume the reader works when put in "MANUAL START" mode? If not - debug here!

Schematic FS-7 of http://bitsavers.informatik.uni-stuttgart.de/pdf/teletype/33/Model_33_Schematic_Jun75.pdf implies that with the automatic reader option a DC1 (XON) will start the reader - as will the START CONTACT (whatever that is).

Here http://www.thocp.net/hardware/teletype_asr.htm states that using a "READER RUN" relay makes XON/XOFF inoperable.

Here http://www.pdp8.net/asr33/pics/main_right.shtml?large shows you a picture of an installed "READER RUN" relay.

I can't see anything from a schematic point of view that would prohibit XON/XOFF and the "READER RUN" relay from operating at the same time.

My guess would be that it depends on what the teletype was connected to originally. If the reader was controlled by a digital contact (READER RUN) then there would be no need for the XON/XOFF support (it would be superfluous) and it could be removed without affecting the installed operation. In fact, leaving XON/XOFF support enabled could cause problems if an XOFF was accidentally sent to the teletype whilst reading a tape (it would erroneously stop!).

It may depend on your particular implementation - so a bit of industrial archeology is probably required.

Can you find the "READER RUN" relay? If so, what is written on the side of it (in terms of operating voltage) and where does it go to (in terms of a connector). Can you see any diodes (if so - you will need to watch the polarity of the operating voltage).

Without this information - it would be difficult to decide on a course of action.

Dave

daver2
June 24th, 2016, 10:46 AM
Bill,

If you have damaged your KIM-1 TTY interface I would check the following:

Check R48 and R49 (150 Ohm) resistors for signs of charring and replace if necessary. These provide Voltage to the teletype current interface.

Measure the Voltage at connector A pins 'R' and 'S' relative to 0V/GND. They should be round about +5Volts.

If the RX side of the teletype interface has gone duff - check CR5 (1N4001), C5 (0.33uF) and Q7 (2N5371) for damage.

If the TX side of the teletype interface has gone duff - check CR6 (1N4001) and U26 (SN7438).

Dave

Moonferret
June 24th, 2016, 01:21 PM
Hi Guy's,

Thanks for the replies.


Doesn't the reader operate by the XON/XOFF (CTRL+Q/CTRL+S) while set to AUTO or was that another option?

Yes, I believe there were a number of options on the readers. Mine has 3 switch positions, START, STOP & FREE. I've seen other machines with 4 switch positions. I'm assuming the 4th is start on XON.


I assume the reader works when put in "MANUAL START" mode? If not - debug here!

Yes, the punch / reader seem to work just fine when the Teletype is in LOCAL mode.
I can also punch fine when online to the KIM. flipping the reader's switch to START when online does nothing.


Here http://www.thocp.net/hardware/teletype_asr.htm states that using a "READER RUN" relay makes XON/XOFF inoperable.

I believe the relay board was designed for uses involving a mini computer where binary data needed to be read/punched. XON/XOFF characters would cause problems here.


Here http://www.pdp8.net/asr33/pics/main_right.shtml?large shows you a picture of an installed "READER RUN" relay.

Hmm, that's quite a bit differrent to what I have...
31809



My guess would be that it depends on what the teletype was connected to originally. If the reader was controlled by a digital contact (READER RUN) then there would be no need for the XON/XOFF support (it would be superfluous) and it could be removed without affecting the installed operation. In fact, leaving XON/XOFF support enabled could cause problems if an XOFF was accidentally sent to the teletype whilst reading a tape (it would erroneously stop!).

Agreed. This Teletype was originally connected to a PDP8 which would back that up.


Can you find the "READER RUN" relay? If so, what is written on the side of it (in terms of operating voltage) and where does it go to (in terms of a connector). Can you see any diodes (if so - you will need to watch the polarity of the operating voltage).

Yup, here are some more photo's...

31810 31811

When I get chance tomorrow, I'll solder a jumper wire across the relay or feed 12V into it and see if it works. I don't want to remove it altogether as I plan to hook up a SCELBI replica at some point and that seems to have circuitry on the TTY interface to support the relay control.

Cheers,
Dave

Dwight Elvey
June 24th, 2016, 09:22 PM
If you look on bitsavers, there is a manual for MCS8 ( intel ) that shows how to
connect on/off for the reader. It might be easy to just reverse it.
Dwight

daver2
June 25th, 2016, 12:09 AM
As you said - somewhat different to the photograph I found...

My information came from the 4-way AUTO option reader. If you have the 3-way switch option then it is a purely manual device (i.e. no XON/XOF support) but it has been fitted (as you say) with the relay option to remotely start the reader. My guess would be that the relay contacts are directly across the contacts for the manual start switch.

At least you know that the relay coil is 12V and there doesn't appear to be any diodes anywhere.

I would follow the wiring back from the relay coil and just energise the relay with 12V (no power to the teletype) to make sure the relay itself energises. Listen for the relay 'click' or use an Ohmmeter to measure the resistance of the relay contact. If you know that works fine - I would then move on to powering up the teletype and seeing if the reader works.

We can then work on a circuit to drive the relay - although you will still need some software to drive the relay at the KIM-1 end. All you should need to drive the relay is a suitably-sized NPN transistor (to handle the relay current), a base resistor (to prevent destroying the transistor) and a 1N4001 diode across the relay coil to prevent the back-emf (generated by the relay coil when the driver transistor switches off) from destroying the transistor. I would also put a capacitor and resistor in series across the emitter/collector junction of the transistor to act as a 'snubber network' (to further protect the transistor). This is pretty much what is shown in the reference Dwight gave (http://bitsavers.informatik.uni-stuttgart.de/pdf/intel/MCS8/8008usersManualRev2_Nov72.pdf page 22 figure 13) but without the snubber network and using pretty much obsolete devices. But you can see the principle.

Dave

Moonferret
June 25th, 2016, 09:53 AM
Dwight, Thanks for the pointer. Descriptions in the manual were very helpful.

Dave, I think what you're describing is very similar to the schematic for the SCELBI TTY card...
http://www.scelbi.com/images/blueprints/scelbi_l.jpg

Not sure if it's really worth adding to the KIM though as the built in monitor doesn't support it but I might add it to my NewBear 7768 as I'm going to have to write / customise some sort of monitor program anyway. May as well make use of the relay while it's there :)

For now, I've just put a jumper wire in to close the circuit without having to power the relay....
31823

This seems to do the trick and I can now load tapes back in. Will probably replace the jumper wire with a switch so I can turn the mod on/off when needed.
So far, I've created tapes for a couple of the games in 'The First Book Of KIM' but I guess I now need to build a memory upgrade and see if I can get Tiny BASIC working. Also need to do a bit more work on the teletype as I occasionally get extra line feeds and the odd wrong character.

Having a great fun though with this kit and thanks again for everyone's help :)

Cheers,
Dave