44
4.2.3 Memory map for V-RAM accessing state
Memory addresses are changed when the V-RAM
is
accessed. The
RAM
addresses in the normal
state range from
$0000
to
$7FFF
for RAM (1), and from $8000
to
$FFFF
for
RAM
(II). When the
V-RAM is accessed, addresses
$DOOO
to
$FFFF
of
RAM (II) are disabled so
that
the
V-RAM will be
access object.
This changeover is effected
by
A
7
of
PIO. When
two
pages
of
graphic V-RAM are used, selection
of
graphic pages
(I)
and (II)
is
made
by
OUT
port
$F4. This operation
is
shown in FIGURE 4.4.
Address
$0000
$7FFF
$8000
$CFFF
$DOOO
$DFFF
$EOOO
RAM
I
RAM
IT
(Option)
RAM
IT
RAM
IT
'
Addr.
Addr.
~:Switching
by PIO
A,
I
Addr.
I
V-RAM
,
,
~ddr.,
Character
~
/Switching
by
OUT
port
$F4
Addr.
Addr.
$FFFFL_
________
~~
V-RAM
Graphic I
(Option)
V-RAM
Graphic
IT
(Option)
Page 1
Page 2
FIGURE
4.4
Switching
of
main memory and V-RAM ( 1)
Address switching
of
the
V-RAM as shown above
is
effected by monitor subroutine PRINT
or
the
like.
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