CHAPTER 4

ADDRESSING RAMCard

The information in this chapter is highly technical and is intended as reference material only.

This chapter describes the addressing of RAMCard. Memory maps showing the addresses used for RAMCard RAM and Apple on-board ROM and a description of the control addresses and their functions make up most of the information. At the end of the chapter, some additional technical details relating to RAMCard and Apple II hardware are described.

RAMCard contains 16K of memory. But, because the memory addresses $C000 through $CFFF are used for the Apple’s I/O, only the 12K of space from $D000 to $FFFF is available to address the 16K of RAMCard. To address all of the 16K of memory on RAMCard, the lower 4K of RAMCard address space is used twice. The programmer can select either of two 4K memory banks to occupy the space from $D000 to $DFFF at one time. This allows 8K of memory to be accessed in only 4K of address space.

Also, RAMCard shares this memory space with the on-board Apple ROMs. The programmer can, therefore, choose whether the memory addresses between $D000 and $FFFF will be used to read ROM or read RAMCard RAM, and whether these same addresses will be write- enabled or write-protected for RAMCard RAM. The selection of these functions plus the selection of which 4K memory bank will be used are performed by accesses to control addresses.

2 1