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SILICON GATE MOS
8255
Printer Interface
APPLICATIONS OF THE 8255
TERMINAL
ADDRESS
STi
PC
3
-
PAo
R
o
8255
PA,
R,
PA
2
R
2
FULLY
PA
3
R
3
DECODED
KEYBOARD
PA
4
R
4
MODE 1 _
PAs
R
s
(INPUT)
PA
6
SHIFT
PA
7
CONTROL
PC
4
STROBE
PC
s
ACK
~
-
PB
o
B
o
PB,
B,
PB
2
B
2
BURROUGHS
SELF·SCAN
PB
3
B
3
DISPLAY
PB
4
B
4
PBs
B
s
MODE 1 _
PB
6
BACKSPACE
(OUTPUT)
PB
7
CLEAR
PC,
DATA
READY
PC
2
ACK
PC
6
BLANKING
PC
o
L.fC
7
CANCEL WORD
UPT~
STi
PC
3
PAo
R
o
PA,
R,
PA
2
R
2
PA
3
R
3
FULLY
MODE 1
DECODED
(INPUT) -
PA
4
R
4
KEYBOARD
PAs
R
s
I PA
6
SHIFT
8255
PA
7
CONTROL
PC
4
STROBE
PC
s
ACKNOWLEDGE
PC
6
BUSY
LT
PC
7
TEST
LT
f-------_--
--
PB
o
....
'0
PB,
--
~
....
PB
2
--
't>
--
"0
MODE 0
PB
3
....
(INPUT) -
PB
4
--
....
PBs
--"",
--
PB
6
....
--
PB
7
....
~
INTERR
REQUEST
INTERRUPT
REQUE
INTERRUPT
REQUE
Keyboard and Display
Interface
HIGH-SPEED
PRINTER
HAMMER
RELAYS
DATA
READY
ACK
PAPER FEED
FORWARD/REV
RIBBON
CARRIAGE
SEN.
DATA
READY
ACK
PAPER FEED
FORWARD/REV
CONTROL LOGIC
AND
DRIVERS
PC,
DATA
READY
PC
2
ACK
8255
MODEl
(OUTPUT)
MODEl
(OUTPUT)
The
8255
is
a very powerful
tool
for
interfacing peripheral
equipment
to
the
8080
microcomputer
system.
It
represents
the
optimum
use
of
available pins and
is
flexible
enough
to
interface almost
any
I/O device
without
the
need
for
ad-
ditional external logic.
Each peripheral device
in
a
Microcomputer
system usually
has a "service
routine"
associated
with
it.
The
routine
man-
ages
the
software interface between
the
device and
the
CPU.
The
functional definition
of
the
8255
is
programmed
by
the
I/O service
routine
and
becomes
an
extension
of
the
sys-
tems software. By examining
the
I/O devices interface char-
acteristics
for
both
data
transfer
and
tim
ing,
and
matching
this information
to
the
examples
and
tables
in
the
Detailed
Operational Description, a
control
word
can
easily
be
de-
veloped
to
initialize
the
8255
to
exactly
"fit"
the
applica-
tion. Here are a few examples
of
typical applications
of
the
8255.
INTERRUPT
REQUEST
INTERRUPT
REQUEST
Keyboard
and
Terminal Address Interface
5-127