The maximum transmission rate of RS232 is 20Kbps, the maximum transmission distance of RS422/485 is 1.2km, and the maximum transmission rate is 10Mbps. 9-pin serial cable can support RS232/422/485.

The maximum relay-free transmission distance of RS485 is 1200m (this value can be exceeded by using low attenuation special cable with impedance matching). If you need repeaters, you can add up to 8 repeaters, which is 9600 meters. The maximum communication distance from RS-232 to RS485 is 1200m, which requires the purchase of a converter.

RS-232 is the most widely used serial interface in PC and communication industry. RS-232 is defined as a single-ended standard, which can increase the communication distance in low-speed serial communication. RS-232 adopts unbalanced transmission mode, so-called single-ended communication.

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In addition to the distance limitation, RS-232 has the following disadvantages:

The signal level of (1) interface is high, which is easy to damage the chip of interface circuit. The voltage of any signal line of RS232 interface has a negative logic relationship, which requires the receiver to recognize the signal above +3V as a logic "0" and the signal below -3V as a logic "1".

(2) Low transmission rate. In asynchronous transmission, the bit rate is 20Kbps. Therefore, on the 5 1CPLD development board, the baud rate of the integrated program can only be 19200.

(3) The interface adopts signal lines and signal loops, forming a male * * * grounding transmission form. This * * * transmission is easily interfered by * * mode, so its anti-noise ability is weak.

Baidu Encyclopedia -RS232 Interface