<s>
IEEE	B-Device
1284	I-Device
is	O
a	O
standard	O
that	O
defines	O
bi-directional	O
parallel	O
communications	O
between	O
computers	O
and	O
other	O
devices	O
.	O
</s>
<s>
It	O
was	O
originally	O
developed	O
in	O
the	O
1970s	O
by	O
Centronics	B-Protocol
,	O
and	O
was	O
widely	O
known	O
as	O
the	O
Centronics	B-Device
port	I-Device
,	O
both	O
before	O
and	O
after	O
its	O
IEEE	O
standardization	O
.	O
</s>
<s>
In	O
the	O
1970s	O
,	O
Centronics	B-Protocol
developed	O
the	O
now-familiar	O
printer	O
parallel	B-Device
port	I-Device
that	O
soon	O
became	O
a	O
de	O
facto	O
standard	O
.	O
</s>
<s>
Centronics	B-Protocol
had	O
introduced	O
the	O
first	O
successful	O
low-cost	O
seven-wire	O
print	O
head	O
,	O
which	O
used	O
a	O
series	O
of	O
solenoids	O
to	O
pull	O
the	O
individual	O
metal	O
pins	O
to	O
strike	O
a	O
ribbon	O
and	O
the	O
paper	O
.	O
</s>
<s>
Each	O
pin	O
is	O
attached	O
to	O
some	O
sort	O
of	O
actuator	O
,	O
a	O
solenoid	O
in	O
the	O
case	O
of	O
Centronics	B-Protocol
,	O
which	O
can	O
pull	O
the	O
pin	O
forward	O
to	O
strike	O
a	O
ribbon	O
and	O
the	O
paper	O
.	O
</s>
<s>
This	O
led	O
to	O
an	O
early	O
expansion	O
of	O
the	O
system	O
introduced	O
by	O
HP	O
,	O
the	O
"	O
Bitronics	B-Device
"	O
implementation	O
released	O
in	O
1992	O
.	O
</s>
<s>
This	O
used	O
the	O
status	O
pins	O
of	O
the	O
original	O
port	O
to	O
form	O
a	O
4-bit	O
parallel	B-Device
port	I-Device
for	O
sending	O
arbitrary	O
data	O
back	O
to	O
the	O
host	O
.	O
</s>
<s>
This	O
proved	O
adaptable	O
,	O
and	O
led	O
to	O
the	O
"	O
Enhanced	B-Device
Parallel	I-Device
Port	I-Device
"	O
standard	O
,	O
which	O
worked	O
like	O
Bi-Directional	O
mode	O
but	O
greatly	O
increased	O
the	O
signalling	O
speeds	O
to	O
2MByte/s	O
,	O
and	O
later	O
the	O
"	O
Extended	O
Capability	O
Port	O
"	O
version	O
increased	O
this	O
to	O
2.5MByte/s	O
.	O
</s>
<s>
In	O
March	O
1994	O
,	O
the	O
IEEE	B-Device
1284	I-Device
specification	O
was	O
released	O
.	O
</s>
<s>
The	O
IEEE	B-Device
1284	I-Device
standard	O
allows	O
for	O
faster	O
throughput	O
and	O
bidirectional	O
data	O
flow	O
with	O
a	O
theoretical	O
maximum	O
throughput	O
of	O
4	O
megabytes	O
per	O
second	O
;	O
actual	O
throughput	O
is	O
around	O
2	O
megabytes/second	O
depending	O
on	O
hardware	O
.	O
</s>
<s>
Since	O
the	O
new	O
standard	O
allowed	O
the	O
peripheral	O
to	O
send	O
large	O
amounts	O
of	O
data	O
back	O
to	O
the	O
host	O
,	O
devices	O
that	O
had	O
previously	O
used	O
SCSI	B-Architecture
interfaces	O
could	O
be	O
produced	O
at	O
a	O
much	O
lower	O
cost	O
.	O
</s>
<s>
This	O
included	O
scanners	B-Application
,	O
tape	O
drives	O
,	O
hard	B-Device
disks	I-Device
,	O
computer	O
networks	O
connected	O
directly	O
via	O
parallel	B-Device
interface	I-Device
,	O
network	O
adapters	O
and	O
other	O
devices	O
.	O
</s>
<s>
No	O
longer	O
was	O
the	O
consumer	O
required	O
to	O
purchase	O
an	O
expensive	O
SCSI	B-Architecture
card	O
—	O
they	O
could	O
simply	O
use	O
their	O
built-in	O
parallel	B-Device
interface	I-Device
.	O
</s>
<s>
The	O
parallel	B-Device
interface	I-Device
has	O
since	O
been	O
mostly	O
displaced	O
by	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
interfaces	O
and	O
USB	B-Protocol
2.0	I-Protocol
.	O
</s>
<s>
IEEE	B-Device
1284	I-Device
can	O
operate	O
in	O
five	O
modes	O
:	O
</s>
<s>
Compatibility	O
Mode	O
,	O
also	O
known	O
as	O
Centronics	B-Protocol
standard	O
or	O
SPP	O
,	O
is	O
a	O
uni-directional	O
implementation	O
with	O
only	O
a	O
few	O
differences	O
from	O
the	O
original	O
Centronics	B-Protocol
design	O
.	O
</s>
<s>
Although	O
never	O
officially	O
supported	O
with	O
these	O
,	O
Nibble	O
Mode	O
works	O
with	O
most	O
of	O
the	O
pre-IEEE-1284	O
Centronics	B-Protocol
interfaces	I-Protocol
as	O
well	O
.	O
</s>
<s>
This	O
mode	O
is	O
supported	O
on	O
a	O
minority	O
of	O
pre-IEEE-1284	O
interfaces	O
as	O
well	O
,	O
such	O
as	O
those	O
built	O
into	O
the	O
IBM	B-Device
PS/2	I-Device
computers	O
;	O
because	O
of	O
this	O
,	O
it	O
is	O
sometimes	O
unofficially	O
called	O
the	O
PS/2	B-Device
mode	O
.	O
</s>
<s>
Enhanced	B-Device
Parallel	I-Device
Port	I-Device
(	O
EPP	O
)	O
is	O
a	O
half-duplex	O
bi-directional	O
interface	O
designed	O
to	O
allow	O
devices	O
like	O
printers	O
,	O
scanners	B-Application
,	O
or	O
storage	O
devices	O
to	O
transmit	O
large	O
amounts	O
of	O
data	O
while	O
quickly	O
being	O
able	O
to	O
switch	O
channel	O
direction	O
.	O
</s>
<s>
Extended	O
Capability	O
Port	O
(	O
ECP	O
)	O
is	O
a	O
half-duplex	O
bi-directional	O
interface	O
similar	O
to	O
EPP	O
,	O
except	O
that	O
PC	O
implementations	O
use	O
direct	B-General_Concept
memory	I-General_Concept
access	I-General_Concept
(	O
usually	O
ISA	B-Architecture
DMA	O
on	O
channel	O
3	O
)	O
to	O
provide	O
even	O
faster	O
data	O
transfer	O
than	O
EPP	O
by	O
having	O
the	O
ISA	B-Architecture
DMA	O
hardware	O
and	O
the	O
parallel	B-Device
port	I-Device
interface	O
hardware	O
handle	O
the	O
work	O
of	O
transferring	O
the	O
data	O
instead	O
of	O
letting	O
the	O
CPU	O
do	O
this	O
work	O
.	O
</s>
<s>
Many	O
devices	O
that	O
interface	O
using	O
this	O
mode	O
support	O
RLE	B-Algorithm
compression	I-Algorithm
.	O
</s>
<s>
ECP	O
can	O
provide	O
up	O
to	O
2.5	O
MByte/s	O
of	O
bandwidth	O
,	O
which	O
is	O
the	O
natural	O
limit	O
of	O
8-bit	O
ISA	B-Architecture
DMA	O
.	O
</s>
<s>
An	O
ECP	O
interface	O
on	O
a	O
PC	O
can	O
improve	O
transfers	O
to	O
pre-IEEE-1284	O
printers	O
as	O
well	O
,	O
by	O
reducing	O
the	O
CPU	O
load	O
during	O
the	O
transfer	O
;	O
however	O
,	O
the	O
transfer	O
in	O
that	O
case	O
is	O
unidirectional	O
.	O
</s>
<s>
Most	O
recent	O
computers	O
that	O
include	O
a	O
parallel	B-Device
port	I-Device
can	O
operate	O
the	O
port	O
in	O
ECP	O
or	O
EPP	O
mode	O
,	O
or	O
both	O
simultaneously	O
.	O
</s>
<s>
IEEE-1284	B-Device
requires	O
that	O
bi-directional	O
device	O
communication	O
is	O
always	O
initiated	O
in	O
Nibble	O
Mode	O
.	O
</s>
<s>
Type	O
A	O
:	O
DB-25	B-Protocol
25	O
pin	O
,	O
for	O
the	O
host	O
connection	O
.	O
</s>
<s>
Type	O
B	O
:	O
Centronics	B-Protocol
(	O
officially	O
called	O
"	O
Micro	B-Protocol
Ribbon	I-Protocol
"	O
)	O
36-pin	O
,	O
for	O
the	O
printer	O
or	O
device	O
connection	O
.	O
</s>
<s>
Type	O
C	O
:	O
Mini-Centronics	O
(	O
MDR36	O
or	O
HPCN36	O
)	O
36-pin	O
,	O
a	O
half-pitch	O
,	O
smaller	O
alternative	O
for	O
the	O
device	O
connection	O
that	O
has	O
not	O
proven	O
popular	O
.	O
</s>
<s>
There	O
are	O
two	O
kinds	O
of	O
IEEE	B-Device
1284	I-Device
cables	O
:	O
</s>
<s>
In	O
IEEE	B-Device
1284	I-Device
Daisy	O
Chain	O
Specification	O
,	O
up	O
to	O
eight	O
devices	O
can	O
be	O
connected	O
to	O
a	O
single	O
parallel	B-Device
port	I-Device
.	O
</s>
<s>
All	O
modes	O
use	O
TTL	B-General_Concept
voltage	O
logic	O
levels	O
,	O
which	O
limits	O
the	O
possible	O
cable	O
length	O
to	O
a	O
few	O
meters	O
unless	O
expensive	O
special	O
cables	O
are	O
used	O
.	O
</s>
<s>
Here	O
are	O
the	O
typical	O
colors	O
found	O
on	O
25-pin	O
IEEE	B-Device
1284	I-Device
cable	O
leads	O
.	O
</s>
