3xLOGIC VISIX Camera - Manual (Page 36)

Installation Manual
|
VISIX
PTZ
Network
Camera
10225 Westmoor Drive, Suite 300, Westminster, CO 80021 | www.3xlogic.com | (877) 3XLOGIC 36
Appendix
4
RS485
Bus
Connection
! General
Property
of
RS485
Bus
According
to
RS485
industry
bus
standard,
RS485
is
a
half-­‐duplex
communication
bus
which
has
120Ω
characteristic
impendence,
the
maximum
load
ability
is
32
payloads
(including
controller
device
and
controlled
device).
! RS485
Bus
Transmission
Distance
When
using
0.56mm
(24AWG)
twisted-­‐pair
line,
according
to
different
baudrate,
the
maximum
transmission
distance
theory
table
is
shown
as
below:
Max.
Distance
of
RS485
Transmission
Baudrate
Max
Distance
2400BPS
1800m
4800BPS
1200m
9600BPS
800m
The
transmission
distance
will
be
decreased
if
we
use
the
thinner
cable,
or
use
this
product
under
the
strong
electromagnetic
interference
situation,
or
there
are
lots
of
devices
are
added
to
the
bus;
on
the
contrary,
the
transmission
distance
will
be
increased.
! Connection
Methods
RS485
industry
bus
standard
require
daisy-­‐chain
connection
method
between
any
devices,
both
sides
have
to
connect
a
120Ω
terminal
resistance
(show
as
Diagram
1),
the
simplified
connection
method
is
shown
as
diagram
2,
but
the
distance
of
“D”
should
not
be
too
long.
Figure
A-­‐7
RS485
Connection
1
Figure
A-­‐8
RS485
Connection
2
! Problems
in
the
Practical
Application
Normally,
users
adopt
star-­‐shape
connection
method
in
construction,
under
this
situation,
the
terminal
resistors
must
be
connected
between
two
farthest
devices
(as
Figure
A-­‐9,
1#
and
15#),
but
this
connection
method
is
not
satisfy
the
requirement
of
the
RS485
industry
standard
so
that
it
will
lead
to
some
problems
such
as
signal
reflection,
anti-­‐jamming
ability
decline
when
the
devices
are
faraway.
At
this
time,
the
dome
will
be
uncontrollable,
or
self-­‐running,
etc.
120Ω 120Ω
1# 2# 3#
4# 32#
D
主控器
A+
B-
A+ B-
1# 2# 3#
31#
Controller