Filter
Top Products
8255A18255A·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
110
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
110
service routine and
becomes
an
extension
of
the system software.
By
ex·
amining the
110
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
PAc
PA,
PA,
PA,
PA,
MODE
1
PAs
(OUTPUT)
PA,
PA,
PC,
PC,
PC,
--!C
4
8255A
PB.
PB,
PB,
PB,
PB,
MODEl
PB,
(OUTPUT)
PB,
PB,
PC,
PC,
ACK
PC.
CONTROL
LOGIC
ANO
DRIVERS
INTERAUPT
REQUEST
Figure 11. Printer Interface
HIGH-SPEED
PRINTER
HAMMER
RELAYS
9-31
INTERRUPT
REQU
EST
I
PC,
8255A
MODE1
(INPUT)
-
PAa
PA,
PA,
PA,
PA,
PAs
PAs
PA,
PC,
PC,
-
-
PB.
PB,
PB,
PB,
PB,
PB,
MODE
1
---.j
PB,
(OUTPUT)
PC.
UPT~
INTERR
REQUEST
,
:
PB
7
I PC,
PC,
i
PCs
~C7
R.
R,
R,
FULLY
R,
DECODED
KEYBOARO
R,
R,
SHIFT
CONTROL
STROBE
ACK
B.
B,
B,
BURROUGHS
SELF-SCAN
B,
DISPLAY
B,
B,
BACKSPACE
CLEAR
DATA READY
ACK
BLANKING
CANCEL
WORD
Figure 18. Keyboard and Display Interface
INTERRUPT
REOU
EST
I
pc,
MODE
1
(INPUT)
8255A
----
MODE 0
(INPUT)
PAc
--
PA,
PA,
PA,
PA,
PAs
PA,
PA,
PC,
PC,
PC,
I
PC,
,--
PB.
PB,
PB,
PB,
PB,
PB,
l PB.
PB,
R.
R,
R,
R,
FULLY
DECODED
R,
KEYBOARD
R,
SHIFT
CONTROL
STROBE
ACKNOWLEDGE
BUSY
LT
TEST
L T
- -
"'0-
--
'1>-
--
'1>-
--
"'0-
--
'1>-
--
t>--
--
0-
--0-.-
-
-
-
-
-
-
-
TERMINAL
ADDRESS
Figure 19. Keyboard and Terminal Address Interface
AFN-00744A-15