<s>
Bus	B-Architecture
contention	I-Architecture
is	O
an	O
undesirable	O
state	O
in	O
computer	B-General_Concept
design	I-General_Concept
where	O
more	O
than	O
one	O
device	O
on	O
a	O
bus	B-General_Concept
attempts	O
to	O
place	O
values	O
on	O
it	O
at	O
the	O
same	O
time	O
.	O
</s>
<s>
Bus	B-Architecture
contention	I-Architecture
is	O
the	O
kind	O
of	O
telecommunication	O
contention	O
that	O
occurs	O
when	O
all	O
communicating	O
devices	O
communicate	O
directly	O
with	O
each	O
other	O
through	O
a	O
single	O
shared	O
channel	O
,	O
and	O
contrasted	O
with	O
"	O
network	O
contention	O
"	O
that	O
occurs	O
when	O
communicating	O
devices	O
communicate	O
indirectly	O
with	O
each	O
other	O
,	O
through	O
point-to-point	O
connections	O
through	O
routers	O
or	O
bridges	O
.	O
</s>
<s>
Bus	B-Architecture
contention	I-Architecture
can	O
lead	O
to	O
erroneous	O
operation	O
,	O
excess	O
power	O
consumption	O
,	O
and	O
,	O
in	O
unusual	O
cases	O
,	O
permanent	O
damage	O
to	O
the	O
hardware	O
—	O
such	O
as	O
burning	O
out	O
a	O
MOSFET	B-Architecture
.	O
</s>
<s>
Most	O
bus	B-General_Concept
architectures	O
requires	O
devices	O
sharing	O
a	O
bus	B-General_Concept
to	O
follow	O
an	O
arbitration	O
protocol	O
carefully	O
designed	O
to	O
make	O
the	O
likelihood	O
of	O
contention	O
negligible	O
.	O
</s>
<s>
However	O
,	O
when	O
devices	O
on	O
the	O
bus	B-General_Concept
have	O
logic	O
errors	O
,	O
manufacturing	O
defects	O
,	O
or	O
are	O
driven	O
beyond	O
their	O
design	O
speeds	O
,	O
arbitration	O
may	O
break	O
down	O
and	O
contention	O
may	O
result	O
.	O
</s>
<s>
Contention	O
may	O
also	O
arise	O
on	O
systems	O
which	O
have	O
a	O
programmable	O
memory	B-Architecture
mapping	I-Architecture
when	O
illegal	O
values	O
are	O
written	O
to	O
the	O
registers	B-General_Concept
controlling	O
the	O
mapping	O
.	O
</s>
<s>
Most	O
small-scale	O
computer	O
systems	O
are	O
carefully	O
designed	O
to	O
avoid	O
bus	B-Architecture
contention	I-Architecture
on	O
the	O
system	B-Architecture
bus	I-Architecture
.	O
</s>
<s>
They	O
use	O
a	O
single	O
device	O
,	O
called	O
bus	B-Architecture
arbiter	I-Architecture
,	O
that	O
controls	O
which	O
device	O
is	O
allowed	O
to	O
drive	O
the	O
bus	B-General_Concept
at	O
each	O
instant	O
,	O
so	O
bus	B-Architecture
contention	I-Architecture
never	O
happens	O
in	O
normal	O
operation	O
.	O
</s>
<s>
The	O
standard	O
solution	O
to	O
bus	B-Architecture
contention	I-Architecture
between	O
memory	O
devices	O
,	O
such	O
as	O
EEPROM	B-General_Concept
and	O
SRAM	B-Architecture
,	O
is	O
the	O
three-state	B-Architecture
bus	I-Architecture
with	O
a	O
bus	B-Architecture
arbiter	I-Architecture
.	O
</s>
<s>
Some	O
networks	O
,	O
such	O
as	O
Token	B-Device
Ring	I-Device
,	O
are	O
also	O
designed	O
to	O
avoid	O
bus	B-Architecture
contention	I-Architecture
,	O
so	O
bus	B-Architecture
contention	I-Architecture
never	O
happens	O
in	O
normal	O
operation	O
.	O
</s>
<s>
Most	O
networks	O
are	O
designed	O
with	O
hardware	O
robust	O
enough	O
to	O
tolerate	O
occasional	O
bus	B-Architecture
contention	I-Architecture
on	O
the	O
network	O
.	O
</s>
<s>
CAN	B-Protocol
bus	I-Protocol
,	O
ALOHAnet	O
,	O
Ethernet	O
,	O
etc.	O
,	O
all	O
experience	O
occasional	O
bus	B-Architecture
contention	I-Architecture
in	O
normal	O
operation	O
,	O
but	O
use	O
some	O
protocol	O
(	O
such	O
as	O
Multiple	O
Access	O
with	O
Collision	O
Avoidance	O
,	O
carrier-sense	O
multiple	O
access	O
with	O
collision	O
detection	O
,	O
or	O
automatic	B-Error_Name
repeat	I-Error_Name
request	I-Error_Name
)	O
to	O
minimize	O
the	O
times	O
that	O
contention	O
occurs	O
,	O
and	O
to	O
re-send	O
data	O
that	O
was	O
corrupted	O
in	O
a	O
packet	O
collision	O
.	O
</s>
