Qvis G3-mini keyboard User Manual - page 16
13
* Connection and terminal resistance
Th e R
S485 standards require a daisychain
co n nec tio n be tw een the e qu ipm en t. T h e re
must
be te rm ina tio n re sista nc e
with 120 Ωat both
e nds o f the c o nne ction
(refer to picture 4-1.1).
Ple ase
refer to picture 4-1.2 for simple
c onn ec tion.
And “ D ” should not
exc e ed 7m .
5. 1 RS485 Bus Basic Knowledge
2400bps
4800bps
9600bps
1800m
1200m
800m
Bau d Rat e
Maximum Di stance
19200bps
600m
Picture 4-1.1
1 20Ω
1#
2#
3#
4#
32#
12 0Ω
Picture 4-1.2
1 20Ω
1 #
2#
3 #
4#
3 2 #
D
A +
B-
A +
B -
1 20Ω
Picture 4-1.3
1#
32#
15#
6#
Mai n Con tr o llo r
120Ω
120Ω
Appendix
* Problems in practical use
If the user adopts a star configuration d u r i n g
practical
connection the termination resistors must be
connected
to the two b i t s o f equipment t h a t are
t h e farthest away from each other, such as
equipment
1# and 15# (refer to picture 4-1.3).
O t h e r w i s e y o u m a y e x p e r i e n c e s i g n a l
r e f l e c t i o n a n d l o s s o f s i g n a l t r a n s m i s s i o n t h e
f u r t h e r a w a y t h e e q u i p m e n t a r e . This connection
way
not b e i n accord a n c e with the
requirements
of RS485 standards in this
installation method. I f y o u h a v e t h e
e q u i p m e n t t o o f a r a w a y y o u w i l l n o t b e
a b l e t o control the dome or continuous l y operate
by itself.
The factory will recommend the R
S485 distributor. The
distributor can transfer the star configuration
connection
to the mode of connection accordance
with the R
S485 standards. The new connection
achieves
reliable data transmission and avoid s the
problem. (refer to
picture 4-1.4)
Rs485 Distributor
B -
1#
2#
3#
120Ω
120Ω
120Ω
A +
Picture 4-1.4
* Characteristic of RS485 Bus line
According to
RS485 standards, RS485 Bus
c o n s i s t s o f half-duplexed data transmission
cables with
characteristic impedance o f
12
0 Ω. The maximum load capacity is 32 unit
loads
(including main controller and controller
equipment)
*
Transmission
distance of RS485 Bus line
When user selects the 0.56mm (24AWG)
twisted
pair as data transmission cable, the maximum
theoretical
transmitting distances are s h o w n
b e l o w according to different baud rate:
If user selects thinner cables, or installs the
camera
in an environment with
a strong electromagnetic
interf erence,
or connects lots of equipment to the
RS485
Bus, the maximum transmitting distance
will
be decreased. To increase the maximum
transmitting
distance , do the contrary.