The "groups" reference is a legacy one where "keyboards" used to provid 16 pairs of control buttons.
as a k83/k84 decoder offered 4 ports, one keyboard could therefore address 4 k83/k84s

The 16 group limit implied, equates to addressing up to 256. this was the controller/keyboard limitation of the earlier 6021 "Central Unit" and 6040 "keyboards"

The k84(k83) themselves are able to be addressed up to box 80 (which multiplied by 4 gives 320).

The newer "Central Stations" (CS1 60212, CS2 60213/4/5 and CS3 60216/60226) are able to address this extra range from 257 to 320 and it is this range that is referenced as groups 17 - 20.

Visually, this aligns with the CS2's screen representation which mirrors a 6040 keyboard with 16 pairs of buttons.

For the CS3 the group reference is meaningless - you just configure the address of an item and give it a name.


However, in the CS3 screens you do need to select "OLD multi-decoder" as the type of decoder.
This will restrict the protocol to MM (Marklin Motorola) and , after you have entered in the address you want, will show a graphic image of what the address switches inside the k84 need to be switched to.


As a final tip - make sure you have the polarity of the red and brown wires correct

The 20(4) reference relates to Keyboard 20 "box" 4

This translates to the k84 port addresses of 317 to 320




Thus it is these addresses that you would use to setup a CS3 article (e.g. a light)

However this is where Marklin try, in my mind, to be too smart without actually understanding how users think in reality.
I offer the following as my interpretation of what they are trying to offer.

To start with, please appreciate that a new k84 (box) reference will not exist, it is inherently created only when you define a device that needs the new decoder
therefore
- select a new item (e.g. light)


- then on the setup screen select
- 0 - the prefered icon
- 1 - "Add MultiDecoder"
- 2 / 3 - confirm "OLD Multidecoder" ... (OLD =k8x, NEW = m8x)
- 4 set address of the k84 port being used
-4a (for reference the OLD decoder will default to MM, but it is possible to alter to DCC for non marklin devices. for the k84 - ensure it is MM)
- 5 - optional , but recommended - set a meaningful name
- - (Here I have conflicting views. Logically it might be nice to name id "20(4).1" given this topics reference to the legacy group IDs. HOWEVER I will point out that Markin (the CS3) allocates it own identification to the "box". In the example you will see the header shows "Multidecoser G" followed by the suffix "G.1" meaning the port. While you can change the G.1, you cannot change the "G". This is important when you come to add items to the other ports of the k84. Some users like to be verbose in their descriptions "Street Lights for Faller Road system" but only so many characters are readable on the subsequent screens. I ,personally, like to include a reference to the address (317) - while this is esentially redundant in operation once you provide a meaningful name it is helpful for debugging and/or event sequences. My thoughts might be something like "G_20(4).1_317")
- 6 once the decoder type (2/3) and the address (4) are supplied, the image (6) will aid in confirming the address setting of the k84.





When it comes to adding items to the other ports of the k84 (addresses 318-320) there are a couple of approaches.
1) (I do not recommend this path)
Start with "Add a new item" as above from the dropdown menu, but instead of Adding a new decode, select an existing one. It is here that you need to know the ID of the existing decoder (in our example "G").
This DOES mean you do not have to worry about step 3 above, and there is some intelligence to automatically increment the next unused address (318). The name is retrieved from the last item with a semi-intelligent sufix added.



2) start the add process from the existing (now created) k84 (as long as you can recall the ID , or the item you first added to the k84. In both cases the edit/setup screen has additional information at the bottom


By clicking on the individual ports at the bottom left, you may find a quicker means to "flesh out" the other ports on the k84
By using this method, the addresses, of the individual ports are already know, as is the protocol and type of decoder
In the image you will see port 2 selected BUT without an item Type (No Article). once an article is selected the ports are further refined. For uncouplers, you may use the red and green individually - thus the reference to 2a and 2b. For a 4 aspect signal, 2 full addresses (4 ports) are allocated.