10Selects on-board ROM read and write-protects RAM.

11Selects 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 Section 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.

C o n t r o l

L a s t D i g i t

F u n c t i o n s / B a n k

Address

( b i n a r y )

 

S e l e c t e d

$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

2 4