☆RS-485 bus is originated from RS-232 bus but that of improving standard, in comparison with RS-232 bus, RS-485 bus’s transmission distance is longer, and the speed is faster. The transmission distance can also reach 120 meters in the speed of 10Mbit/s.the maximum transmission speed can reach 90 Kbit/s when the furthest distance is 1200 meters; because a different transmission adopted by RS-485 results in higher CMRR . With the replaced bus of RS-232, RS-485 perfectly resolves the problems what RS-232 has in data transmission of industry control, such as short transmission distance, low transmission speed, and being liable to be disturbed etc.

☆RS-485 bus main feature: 

    Half-duplex communication，if need full duplex communication, it can be used two sets of RS-485 bus to compose as RS-422A bus.
Long transmission distance, the maximum distance can reach 1200 meters，meanwhile, the highest transmission speed can reach 90Kbit/s。
High transmission speed, the maximum speed can reach 10Mbit/s，meanwhile, the furthest transmission distance can reach 120 meters.
Differential transmission has higher CMRR, and strong capacity of resisting IPC disturbance.
Compatibility with RS-232C, it can perfectly work by directly replacing the interface CMOS chip and cable of R-232 (depending on the status).
More transmission lines, half-duplex needs three lines (the ground wire is optional); full-duplex needs five lines (the ground wire is optional).
Non-intelligent bus, do not support concurrent transmission and competitive judgment, if concurrent transmission occurs which the error will happen.

☆Advantage:

    for the single node, lower the cost of the electro circuit, designed easy, and convenience implementation.

☆Shortage: 

    the reliability is not so good, it's possible for the error in single node to lead the whole network to be paralyzed; the component of RS-485 is easy to be damaged; and it is difficult to identify the error node of the network, the maintenance fee is much higher.

☆Application range:

    The number of node is less, the distance of transmission is about 1 kilometer, it is more fit for the places where require the low security.