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PX.
13.
3
ROM
(Read
Only
Memory)
The
ROMs
used here
include a
32K
X
8-bit
masking
ROM
YM-2301-23908
(IC12)
with
built-in
MSX-BASIC (UK
version)
and
a
8K
X
8-bit
masking
ROM
PD5031
(or
EP-ROM
M5L2764K-
213) (IC13) with
built-in
P-BASIC
(for
extension
BASIC).
13.
3.
1
ROM
Accessing
13.
3.
2
P-BASIC
ROM
Selection
The P-BASIC
ROM
is
allocated
to
addresses
4000(H)
thru
5FFF(H)
of
slot
2
(8K
bytes),
and
is
selected
when
a
P-BASIC
extension
command
is
used
or
an
interrupt
is
generated.
The
selection
operation
involves
CS
being switched
to
L when
the
4000(H)
thru
5FFF(H)
memory
is
read
at
SLTSL2-*L.
The
MSX-ROM
is
allocated to addresses
0000(H)
thru
7FFF(H)
of
slot
0
(32K
bytes),
and
is
normal-
ly
selected
when
the
power
i
s
swi
tched on. This
MSX-RO
M
is
selected
when
MERQ=L,
RD=L,
and
SLTSL0=L
at
memory
addresses
0000(H)
thru
7FFF(H)
(A15-*-L).
And
as
will
be
d
escribed
later
(13.7.1),
an
L
output
from
SLTSL0
is
generated
automatically
when
the
power
is
switched
on
or
when
the
RESET
button
is
pressed, resulting
in
the
MSX-ROM
being
selected
and
MSX
BASIC
being
activated.
CS
SW
ITCHEO TO
L
WHEI
SLTSL2
—
L AND 4000
H
1
5FFFH
MEMORY
IS
READ
Fig.
13-9
ROM
circuit
Table
13-1
ROM
is
selected
when
MERQ,
RD, and
SLTSLO
are at
L
at
memory
addresses
0
thru
7FFFH
(A15—
L)
The
CS1, CS2,
and
CS12
output
signals
are
passed to the
connector
section for
slots
1
and
3.
CS1 (4000H
thru
7FFFH)
is
also
used
as
P-BASIC
ROM
selector
signal.
"0"
in this
table
denotes
L
level,
and
"1 " denotes
H.
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