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8255A18255A·5
Input Control Signal Definition
STB (Strobe Input). A "low" on
this
input
loads
data
into
the
input latch.
IBF (Input Buffer Full F/F)
A "high" on this
output
indicates
that
the data has been
loaded into the input latch;
in
essence,
an
acknowledgement
IBF
is
set by
STB
input being low and
is
reset by the rising
edge of the
RD
input.
INTR (Interrupt Request)
A "high" on this
output
can be used to interrupt the
CPU
when
an
input device
is
requesting service.
INTR
is
set by
the
STB
is
a
"one",
IBF
is
a
"one"
and
INTE
is
a "one".
It
is
reset by the falling edge of
RD.
This procedure allows
an input device
to
request service from the
CPU
by simply
strobi
ng
its data into the port.
IBF
INTR
INTE
A
Controlled by bit set/reset
of
PC
4
.
INTE
B
Controlled by bit set/reset of
PC2.
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MODE
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Figure 6.
MODE
1 Input
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INPUT FROM
PERIPHERAL
---
---------------------
.
...
.
Figure 7.
MODE
1 (Strobed Input)
9-25
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