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Appendix RS485 Bus-mastering knowledge
RS485 Bus-mastering basic characteristics
According to RS485 bus-mastering standard,RS485 bus for half-duplex communication bus,its
maximum load capacity is 32 payload(including main controller and controlled set)
RS485 bus-mastering transmission distance.
When you use Twisted pair with 0.56mm(24AWG) for communication cable,The baud rate is
different.The Max. Transmission distance theoretical value as shown below:
Baud Rate
Max. Distance
2400BPS 1800m
4800BPS 1200m
9600BPS 800m
When you use our products with thin cable or in strong electromagnetic interference
environment.The Max.transmission distance will be shorten.Opposite,The Max.transmission distance will
be longest.
Problem in practical application
Customer often use star type connection method in installation,So the termination resistors must
connect to the equipments which these two devices spacing farthest in distance.( as follow,1# and 15#
devices ),But this connection method is not comply with RS485 standard provisions,Various equipments
have more longer distance,Easy to form signal reflections and decline in anti-jamming capability,lead to
the control signal is weak.The speed dome will not be controlled or can not stop moving in this time.
