1. RS-485/RS-485 bus, requiring communication distance of tens of meters to a kilometer, the widely used RS-485 serial bus RS-485 balanced differential transmit and receive, so it has the ability to suppress common mode interference. Plus bus transceiver with high sensitivity, can detect voltages as low as 200mV, so the transmitted signal can be restored at outside kilometers. RS-485 half-duplex mode, any time there can be only a little in the sending state, therefore, the enable signal transmission circuit shall be controlled. RS-485 for multi-point interconnects is very convenient, you can save a lot of signal lines. RS-485 can be networked applications constitute a distributed system, which allows up to 32 parallel drive and 32 receivers. 3, RS422 bus, RS485 and RS422 circuit is basically the same principle, they are sending and receiving differentially, no digital ground. Work is under rate differential with the condition of the root causes of transmission distance, which is the fundamental difference between the two and RS232 because RS232 is a single-ended input and output, at least when duplexing digital ground work. Send and receive wire line three lines (asynchronous transmission), you can also add other control line to complete synchronization. RS422 full duplex by two pairs of twisted pair transceivers work independently of each other, but only half-duplex RS485, can not send and receive at the same time, but it only needs a twisted pair. RS422 and RS485 at 19kpbs can transmit 1200 meters. Line with the new transceiver devices can be connected.

2. RS-232-C/RS-232-C is a serial physical interface standard American Electronics Industry Association EIA (Electronic Industry Association) to develop. RS is the English “recommended standard” the acronym for the identification number 232, C represents the number of changes. RS-232-C bus standard has 25 signal lines including a main channel and a secondary channel. In most cases, the main use of the main channel, duplex communication in general, only a few signal lines can be achieved, such as sending a line, a receiving line and a ground line. RS-232-C standard specifies a data transfer rate of 50, 75, 100, 150, 300, 600, 1200, 2400, 4800, 9600, 19200 per baud. RS-232-C standard, the drive allows 2500pF capacitive load, the communication distance will be affected by this capacitance limits, for example, using the communication cable 150pF / m, the maximum communication distance of 15m; if cable capacitance per meter is reduced , the communication distance can be increased. Another reason is the short transmission distance RS-232 is a single-ended signal transmission, there is a common ground can not suppress common mode noise and interference problems, it is generally used for communication within 20m.