...
Note, however, that cards with an addressing range of less than 1M (which at time of writing means all of them!) only decode the lower address lines, so for example a 32K RAM card in slot 1 will appear identically in banks &40 and &41, &42 and &43 .... &7E and &7F, ie. whatever the state of the top 5 address lines. A 128K EPROM card (in slot 3) would appear identically in banks &C0 to &C7, &C8 to &CF, &D0 to &D8 ... &F8 to &FF. This makes it easy to address the top and bottom of its address space without prior knowlege of its size ie. by addressing the top and bottom bank of the slot. The system expects this behaviour so the convention should be followed by any hardware developers intending to create their own cards.
Hybrid cards
Note that it is possible to mix ROM and RAM in a single card, but care must taken in decoding the address lines. A simple scheme, which should work, is to have the lower half of a card containing RAM (the RAM can occur several times in first half megabyte) and the upper half ROM (again the ROM can repeat). If a card is arranged like this the system will be able to use the RAM and run software from the ROM. Other schemes exist which can make on-card RAM private. If you intend to develop hybrid ROM and RAM cards, you are strongly advised to consult Cambridge Computer.