Nat Semi SC/MP Low Cost Development System

[Realtime]

I've been a bit quiet on this (been pulling my hair out trying to understand the code). I decided to strip the code back to almost nothing, just a routine to service the display and even that didn't do anything. So I made a harness to use the MK14 as an EPROM emulator for the TELEKIT. I was originally going to use Coolsnaz2's dual port ram VDU card for this but settled on the MK14 for 2 reasons. 1) as most of the TELEKIT functionality is based on SIO and FLAG activity I would be able to load the code into the MK14, see how it runs on the MK14's processor and then switch over to see how it compares on the TELEKIT processor (albeit at half the speed). 2) the MK14 has Coolsnaz2's fast loader so the turn around time for making and testing changes is short.

One thing I found is that ENIN has been left floating on the TELEKIT. There's no indication in the ISP/8A-500 datasheet that that's allowed so I have added a pull up resistor. I've replaced both SRAMs as one was definitely faulty and also replaced the 74LS04 as the logic levels looked weird on some pins.

And now, I can write to the display and see the keypad scan happening That's a relief as that alone tests about 90% of the card.

Unfortunately loading up the full (original) code still results in a blank display but at least I have a means of building the code up again to see what's going astray.

[circuitryboy]

Excellent advance there. It's good to see the display in action.
Yes, the firmware does seem to be something of a Mare's Nest. The original pic shows the MM5204Q labelled
'TELEKIT' without any version/level number. Had the window been taped and then cut away?
Suggests reprogrammed - work in progress.

Did you find any high-resistance contacts within the keypad matrix?

[Realtime]

Originally Posted by circuitryboy

Excellent advance there. It's good to see the display in action.
Yes, the firmware does seem to be something of a Mare's Nest. The original pic shows the MM5204Q labelled
'TELEKIT' without any version/level number. Had the window been taped and then cut away?
Suggests reprogrammed - work in progress. Did you find any high-resistance contacts within the keypad matrix?

Definitely was a work-in-progress. As for the keypad I haven't reconnected it yet. I don't want to keep stressing the flexi each time it's moved out of the way.

Originally Posted by circuitryboy

. ...... Right at the end before cycling back to $0001. Looks like a Bug!

Yes, I'd been wondering about that jump to START and it really didn't make sense. So I changed it to JMP LAB002, which is the start of the main loop. That resulted in some random looking but repeatable characters being displayed when a message was received over the TTY interface from the LCDS. A bit more digging and I found the timing variable for the received TTY baud rate. +$45(P2) was set to 9 - a bit of experimenting led to a value of 6 being used. Now the TELEKIT correctly receives and displays the message from the LCDS, namely CL 0001 <CR>.

I've captured that in the very short attached video. I added some code to initialise the display to -tELEKit- at power on. This then gets shifted out to the left as new characters are received from the LCDS.

Phew. Next is to figure out how keypresses should be handled, but that's enough progress for this weekend. My wife thinks I left home Friday afternoon!!

[Timbucus]

Ah that is lovely to see some text moving- well done on the effort involved there and the risks to marital bliss taken in the name of retro archaeology

[circuitryboy]

Originally Posted by Realtime

As for the keypad I haven't reconnected it yet. I don't want to keep stressing the flexi each time it's moved out of the way.

Of course. I understand your concern.
In the pics it looks like the flexi contacts are 0.1in spaced.
Would it be possible to improvise a 'ZIF' connector where the contacts are gently clamped against flat 'Vero' strips,
gold edge connectors, whatever? Then the disconnected matrix could be mapped, assuming keypresses are detectable.

[Realtime]

Originally Posted by Timbucus

Ah that is lovely to see some text moving- well done on the effort involved there and the risks to marital bliss taken in the name of retro archaeology

. I forgot to say that the video is slowed down to 40% of full speed to make it easier to read as it shifts along.

Originally Posted by circuitryboy

Would it be possible to improvise a 'ZIF' connector where the contacts are gently clamped against flat 'Vero' strips, gold edge connectors, whatever? Then the disconnected matrix could be mapped, assuming keypresses are detectable.

I really like that idea. I’ll give it a go at the weekend.

[Realtime]

On the Old Computers Introkit forum page, at the bottom of the page, is a chap called Frank Boehm (Germany) who stated back in 2007 "Just received a "Telekit" - made by National Semiconductor, datecode 7618. This is pretty much the same electronics, but built into one of their larger pocket calculator cases (looks like the Mathematician PR 4640 with different key mappings). It has an external cable probably to attach it to a tty terminal".

Does anyone recognise Frank from this or other forums? It would be really interesting to contact him and see what he knows.

[circuitryboy]

I found this. But digging deeper fails.
I think perhaps because it's "archived" and gone missing?

[Mark1960]

I saw that too, he doesn’t seem to have been active since about 2013.

It might be worth asking about the telekit on any active forum for collectors of calculators. Frank might not reply but someone else might have seen one or collected one.