Intel MCS48 User Manual page 324

8255A/8255A-5
APPLICATIONS OF THE
8255A
The 8255A
is
a very
powerful
tool for interfacing
peripheral equipment
to the microcomputer
system.
It
represents the
optimum
use
of available pins
and
is
flex-
ible
enough
to interface
almost any
I/O
device without
the
need
for additional external
logic.
Each
peripheral device
in
a
microcomputer system
usually has a
"service routine" associated with
it.
The
routine
manages
the software
interface
between
the
device
and
the CPU. The
functional
definition of
the
8255A
is
programmed
by the
I/O
service routine
and
becomes
an extension
of
the
system
software.
By
ex-
amining
the
I/O
devices
interface characteristics for
both data
transfer
and
timing,
and matching
this infor-
mation
to the
examples and
tables
in
the detailed opera-
tional description,
a
control
word can
easily
be
devel-
oped
to
initialize
the 8255A
to exactly
"fit"
the applica-
tion.
Figures 17 through 23 present a few examples
of
typical applications of the 8255A.
INTERRUPT
REQUEST
"
MODE1
(OUTPUT)
MODE1
(OUTPUT)
PAo
INTERRUPT
REQUEST
3
DATA READY
ACK
PAPER FEED
FORWARD/REV
DATA READY
ACK
HIGHSPEED
PRINTER
HAMMER
RELAYS
DATA READY
ACK
PAPER FEED
FORWARD/REV
RIBBON
CARRIAGE
SEN.
CONTROL
LOGIC
AND
DRIVERS
Figure
17. Printer Interface
INTERRUPT
REQUEST
"
PC
3
8255A
MODE
1
(INPUT)
PAo
PA,
PA
2
PA
3
PA
4
PAs
PA
6
PA
7
PC„
_PC
5
R
«1
R
2
FULLY
R
DECODED
3
KEYBOARD
R
4
R
5
SHIFT
CONTROL
STROBE
ACK
PBo
PB,
PB
2
p
B
3
PB
4
p B
5
MODE
1
PR
(OUTPUT)
B
6
PB,
PC,
PC
2
|
PC
6
PC L?C
7
B
o
B,
B
BURROUGHS
2
SELF-SCAN
B
3
DISPLAY
B
4
B
5
BACKSPACE
CLEAR
DATA READY
ACK
BLANKING
CANCEL
WORD
INTERRUPT
REQUEST
ZI
Figure
18.
Keyboard and
Display Interface
-n
pc
3
MODE
1
(INPUT)
8255A
"PAo
PA,
PA
2
PA
3
p
A
4
PAs
PAe
PA
7
PC
4
pc
5
pc
6
[pc
7
R
«1
R
2
B
FULLY
3
DECODED
r
4
KEYBOARD
SHIFT
CONTROL
STROBE
ACKNOWLEDGE
BUSY
LT
TEST LT
MODE
(INPUT)
P"o
PB,
PB
2
p B
3
PB
4
PB
5
p B
6
.
PB
7
tf~~
">,
<S~
~"o
TERMINAL
ADDRESS
Figure
19.
Keyboard and
Terminal Address
Interface
8-34
00744A