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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 hard-
ware 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.
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