Serial Port Small note

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Serial communication: Including RS232C RS485 RS422 USB, etc.;

RS232C transmission distance maximum 15m, transmission speed maximum 20kb/s; Reason:

1) The RS232C standard stipulates that the driver is allowed to have 2500PF capacitive load, for example: When using 150pf/m communication cable, the maximum transmission distance is 15m, if the capacitance of each meter is reduced, the communication distance can be increased;

2) rs232c is a single-ended signal transmission, there are common noise and can not suppress common mode interference, and so on, so the general transmission distance of not more than 15m.

RS232C Level characteristics:

Send side: Positive flat +5v-15v--0 negative -5v--15v--1

Receiving end: Positive flat +3v-12v--0 negative -3v--12v--1

Because the transmit level and the receiving level are only 2-3v, the common mode rejection is poor.

The difference between the three-wire system and the nine-line serial port: The nine-wire system is RS232C standard, the security, stability is higher than the three-wire system, but the nine-line design cost, designers in the use of summed up, to achieve the most basic communication, only need to use Rx, TX and GND.

Serial Port Small note