Thanks for the document, @pl212.  You've probably seen the MCL'82 protocol document (attached) that I uploaded a few months back.  It represents the final variant of MCL1 before the release of MCL2 (Datalink '86).  There was almost no documentation that I could find when I assembled this protocol document, which was created mostly by me spying on the messages being passed between a Beomaster 5000 and MCP 5000.  There are still a few straggler messages whose meaning I have yet to fully decipher, which I hope to get to some day. I recently acquired an original MCP, designed for use with the Beocenter 7700 (which I don't yet have).  Just based on the jumpers I see in the 2041 relay boxes, I'm thinking the MCP instruction set is unique to the 7700 - or at least the response messages will be - but I'd venture to guess there will be some overlap in the command set between the MCP and MCP 5000.  Having just the MCP, I'll be able to verify outbound commands for starters.  If you happen to have a Beocenter 7700, perhaps you can add to the knowledge-base by providing the responses for the documentation. I'm in Marin, so we're close by each other, and can get together to compare notes over lunch, if you're interested.  

https://archive.org/details/1983-bang-olufsen-master-control-link-system/ I find these early MCL systems fascinating, not because they were perfect (lots of issues about incomplete remote control) but because they were a fledgling attempt to get whole-house automation working over just a few extra pins in a speaker cable!

Very interesting to see that this document also existed, and seems to be before it was rebranded to MCL82, but also only Beocenter  7700 is mentioned in the manual where later a fwew more systems were supported. I have scanned the installation and user manual that came in the MCL82 packages, and there are available here at Beoworld in the products section under Beolink, but this manual seems to be more  thorough  about hidden installation types.  

 ) the jumper positions can be:

• Beocenter 7000/7002
• Beoceter 7007/7700 Link room
• Beocenter 7007/7700 Center room
• Beomaster 5000 / Other

So yes there seem to be some differences between systems, probably due to different remotes for the products  

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Location: Denmark