titus-larsen-titus-1981-apple-interfacing

of an examined memory location. From the previous discussion of
memory devices, you should realize that the POKE operation will
have no effect on the read-only memory devices in the Apple.
Memory Maps
At this point it is a good idea to take a look at the "maps" of the
memory addresses that are used by the Apple. A complete 64K memory
map is shown in Fig. 1-3. For the sake of convenience, the memory
addresses are provided in both decimal (base-10) and hexadecimal
(base-16) notation. The hexadecimal numbers have a suffix of
"H'' to distinguish them from the decimal numbers.
The memory space for the Apple computer has been divided into
four 16K blocks. Three of the blocks have been assigned for R/W
memory, and most Apple computers have the R/W #1 block "filled"
with read/write memory chips. The remaining R/W blocks may be
used for future expansion of R/W memory, if this is required for particular
applications. In most cases, we have found that 16K of R/W
memory is sufficient. Add-on memory chip kits are available from
many suppliers, and most Apple users can probably add the additional
memory chips to their system without much difficulty.
The remaining 16K block of memory has been set aside for both
ROM and 1/0 port addressing. The system ROMs for the Apple,
which include the BASIC interpreter and the monitor programs, take
up 12K of this space. The remaining 4K space is divided into two 2K
spaces for I/ 0 addressing and future expansion of the Apple. The
I/ 0 block with addresses COOOH to C7FFH, inclusive, is the one
of major importance for interfacing, since it has been specifically set
aside for this purpose and it will never be used in Apple computer
systems for any other purpose. Some of the addresses within this 2K
block have been used by the Apple for controlling things such as the
speaker, the keyboard, and the cassette recorder. The actual address
49152 COOOH
0 OOOOH 51199 C7FFH
2K 1/0 #1 /51200 C800H
16K R/W#l
.
16383 3FFFH
2K 110 #2
-
53247 CFFFH
16384 4000H
53243 DOOOH
16K R/W#2
12K SYSTEM ROMS
32767 7FFFH
32768 8000H -65535 FFFFH
16K
49151 BFFFH EXPANDED VIEW OF UPPER 16K
49152 COOOH
65535 FFFFH
16K
Fig. 1-3. 64K Memory map for the Apple computer.
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