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PX-
13.
5.
2
Extension I/O
Interface
The
I/O address allocation
is
stipulated
by
MSX
(see
Table
13-3),
and no
other I/O can
be
allocated
to
an I/O
address.
If
a
hypothetical I/O
register
is
set in
the
memory
address
of
a suitable
slot
by
the
memory
mapped
I/O
method,
other I/Os can be
set
in
this register.
The
extension I/O
is
placed
in
memory
address
7FFEH (LCON
register)
and
7FFFH (VCON
register)
of
slot
2
by
the
memory
mapped
I/O
method
for
exchange
with the
CPU.
The
extended I/O
interface
is
used
in
video,
audio,
and
syste
m
contro
l
wit
h
accessing
executed
by
AO
thru
A15,
SLTSL2,
WR,
and
RD
to generate
the following
signals.
LCONW
L when
7FFEH
writing
LCONR
L
when
7FFEH
reading
VCONW
L when
7FFFH
writing
VCONR
L when
7FFFH
reading
The
bit
allocation for
memory
addresses
7FFEH
and
7FFFH
is
outlined
in
Tables 13-4
and
13-5.
by
AO
thr
Fig.
13-15 Extended I/O
interface
Table
13-4
Expansion
I/O
resisters
(Slot
#2)
LCON
register
<7FFE (16»
Table 13-5
Expansion
I/O
registers (slot
#2)
VCON
resister
<7FFF
(16)>
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