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APPLICATION
EXAMPLES
40
|26
J20
Vcc
Vdd
Vss
XTAL1
8049
8048
8748
P22
P23
P24
P25
P26
P27
DBO
DB1
DB2
DB3
DB4
DB5
DB6
DB7
ALE
PSEN
PROG
WR
RD
-W\
IN2
-VA
IN3
-Wv
IN5
-V/v
IN7
The
bus
is
normally used as an output
port.
To
use
it
as
an
input port the
bus
is
put
in
the high
impedance
state
using the
MOVX
instruction
and
then read using the
INS
instruction.
The
resistor
value
chosen
is
a function
of
the
output loading
and
the characteristics
of
the
input
signals.
ADDING
8
INPUT
LINES
Vcc
Vdd
Vss
XTAL
1
8049
8048
8748
P22
P23
P24
P25
P26
P27
DBO
DB1
DB2
DB3
DB4
DB5
DB6
DB7
ALE
PSEN
PROG
WR
RD
S=-
74LS259
(16)
Individual
bits
of
the
74LS259
eight-bit
addressable
latch
can be
set
or
reset
using the
OUTL
instruction.
During
the
OUTL
operation
bit
zero
of
the
accumulator
is
written
into
the
bit
of
the
latch
specified
by
bits
1
through
3
of
the
accumulator.
In
this
configuration
DBo-
DB7
will
be momentarily
disturbed while the
external
latch
is
loaded.
ADDING
8
OUTPUT
LINES
5-14
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