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only 12K ($D000-$FFFF) of address space is available for 16K
RAM. Using the control addresses to switch between the two
4K banks allows you to address 8K RAM with only 4K of
address space.
The remainder of the RAMCard RAM ($E000-$FFFF) is di-
rectly addressable.
Control addresses are entered either in hexadecimal, for assembly lan-
guage programs, or in decimal, for BASIC programs. Hexadecimal
addresses begin with the dollar sign ($).
All of the hexadecimal control addresses have the form $C08x. x is any
of the hexadecimal digits 0-3,8-9,A-B. The value of x determines the
bank and which functions are selected. When the value of x is convert-
ed to binary, then the functions associated with the bit positions can be
seen more clearly.
The hexadecimal digits 0-3,8-9,A-B convert to binary as follows:
HEX BINARY
0 0 0 00
1 0 0 01
2 0 0 10
3 0 0 11
8 1 0 00
9 1 0 01
A 1 0 10
B 1 0 11
Bits 0 and 1 (the two right columns of each binary number) are read
together to select the functions. As you can see there are only four
selections — 00, 01, 10, 11. These selections are repeated.
Bits 0 and 1 together select the following functions:
00 Selects RAMCard RAM read and RAM write-protect.
01 Selects on-board ROM read. Two or more successive reads to the
address write-enables RAMCard RAM.
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