Cable info to connect a Mega ST keyboard to a standard ST

[JezC]

Hi, I'm hoping someone can help point me in the right direction.

I've got an original Mega ST keyboard & used to have this connected into a stock ST with an adaptor cable.

Sadly I've yet to find this cable & want to use the Mega keyboard with an ST (which has a broken keyboard) so I was wondering if anyone can provide the wiring info I would need to make a new cable (or two).

I believe that others are also interested in these details so if I find the lead I will obviously spread the knowledge.

TIA

[DoG]

Keyboard connectors all Ataris.png (102.48 KiB) Viewed 9668 times

[JezC]

Fantastic!
I'll trawl through my parts and order up anything I'm missing.
Thanks for the info, much appreciated.

[rubber_jonnie]

Thought I'd add this as I need to build an adapter, hopefully it'll help somebody else too.

Mega_2_ST_KBD_Corrected.png (31.26 KiB) Viewed 8659 times

EDIT: 04/04/2020 Picture corrected to show correct TX/RX connection

[DoG]

It seems that my first post is a bit wrong. Tx should connect to Rx for it to work. And Rx to Tx. Would be great if you could confirm this and update us when you have tested the cable.

So pin 5 on the Atari to pin 3 on the RJ12 (MegaST connector).
Pin 6 on the Atari to pin 4 on the RJ12.

Mega ST keyboard connector pinout.jpg (25.83 KiB) Viewed 8877 times

keyboard schematics Atari ST.jpg (34.98 KiB) Viewed 8876 times

[rubber_jonnie]

@DoG Cool I am hoping to have a look at this over the weekend, I'll let you know and I'll update my diagram too.

[rubber_jonnie]

So, what with postal delays, my RJ12 sockets literally just arrived today, so hopefully over the weekend I can have a look at wiring something up.

[Steve]

Yeah I can confirm dogs picture has that tx rx error, when I was building my rj12 port on my falcon for an external keyboard it really confused me at the time.

http://atari-forum.com/viewtopic.php?f=27&t=37822

Here is my process as I did troubleshooting. Might be helpful.

[rubber_jonnie]

Cool, thanks @Steve

[rubber_jonnie]

Hmm, into head scratching mode now. I've wired up an RJ12 socket as follows:

Mega_2_ST_KBD_Corrected.png (31.26 KiB) Viewed 8574 times

The keyboard has power as the power LED is lit, but it's not working when plugged into my Mega ST. I've tried reversing the TX/RX connections as mentioned further up the post but no different.

I'm now wondering, that as I'm trying to connect the opposite way i.e. STFM KBD to Mega ST, if it actually works in reverse. I'd expect it should, but if anyone has any ideas I'd be grateful.