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10 Selects on-board ROM read and write-protects RAM.
11 Selects RAMCard RAM read. Two or more successive reads
to the address write-enables RAM.
When ROM is selected, the Apple II on-board ROM is selected for the
address space $D000-$FFFF. Refer back to the memory maps in Sec-
tion 3.1 for an illustration of these relationships.
Notice that it is possible to write to the RAMCard RAM and read from
on-board ROMs at the same time (01 above).
Bit 2 (the third column from the right) is ignored.
Bit 3 (the left column) selects which 4K bank will be accessible. If bit 3
is zero (x is between $t)-$3), then BANK 2 will be mapped into D000-
$DFFF. If bit 3 is one (x is between $8-$B), then BANK 1 will be
mapped into $D000-$DFFF. When one bank is selected, the other bank
is not available.
Power-on/RESET selects on-board ROM read (disables RAMCard
RAM read), write-enables RAMCard RAM, and selects mapping of
BANK 2 in the address space $D000-$DFFF. This is identical to two
consecutive accesses of $C081 -
The various selections are summarized in the chart below. Both the
hexadecimal and decimal control addresses are shown in the first
column.
Control Last Digit Functions/Bank
Address (binary) Selected
$C080
—16256 0000 Selects RAMCard RAM read, BANK 2, and
RAM write-protect
$C081
—16255 0001 Selects Apple on-board ROM read, BANK 2,
and write-enables RAMCard RAM if address
accessed twice consecutively
$C082
—16254 0010 Selects Apple on-board ROM read, BANK 2,
and RAMCard RAM write-protect
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