What is it?
The Amiga 1200 (like the CDTV) did not have a battery backed up clock but instead had a small connector on the motherboard that let the user plug a battery in if required, This slot was called the clock port.

What can I fit in it?
Well unlike the CDTV there was only one place you could upgrade the Amiga 1200 and this was almost always full so developers turned to this little 22 pin connector and pushed it to where it was never meant to go, Now the Amiga 1200 can have 16 bit sound cards with hardware Mpeg audio decoding, super fast serial cards and ECP parallel ports.
The CDTV clock port adapter can not have a battery fitted to power the clock but can have the above cards plugged into it (Although most drivers where designed for Workbench 3.0 so wont work on the CDTV unless you upgrade the OS).

How much is it and how much are the cards for it?
The card isn't sold complete, Just the PCB is available from Kato development but the components are available from any electronics store (The parts are all very basic electronics) unfortunately I haven't been able to buy any of these cards but the PCB should be very cheap.
The serial cards are between £16 and £25 (Depends where you buy it more than the make).
The parallel cards are £20 to £25 and are all ECP compatible.
The sound cards are between £100 and £125 (Depends what card you go for, All are 16Bit).

You can find out more information @ http://www.katodev.de (German only) where a PCB layout is available for you DIY people.