The CPM card should be connected with the ATOM by means of a VIA. Members from the region Den Haag developed in 1987 an eurocard with the VIA 6522, addressed on #BC00. On this card are also extra sockets provided for 1 x RAM type 6116 and 2 sockets to be used by an Eprom type 2532.
The socket for the 6116 offers the possibility for RAM on #2000 - #27FF, the Dos catalogue buffer. Unavoidable as the Acorn Dos is not anymore in use and you don't have any Ram on that address. The memory space #Exxx is then available also.
By placing two EPROMs on #Exxx you are able to switch between the old Atom Dos and #A000 - #AFFF for an extra A-block in Eprom
#C000 - #CFFF for an modified C-ROM
#D000 - #DFFF for an modified D-ROM floating-point
#E000 - #EFFF to use the Atom end / or G-Dos
#F000 - #FFFF for an modified F-ROM

The concerning addresses have to be "outside the bus". The RAM- ROM sockets are optional. A singlesided pc-board with a number of jumpers is developed.