Basic knowledge of the RS232 serial interface

At present there are 9 needle is relatively commonly used RS232 serial port D shape serial interface [ DB9] And the 25 needles D shape serial interface [ DB25] , the maximum communication distance of [ 15 m] 。 The distance of two devices close, can use 232 cable to their 232 connected to a serial port directly; If the distance is far, can through the modem ( 调制解调器) Attached to it. RS232 interface - — When using 'negative logic' - — Output terminal with + 5 v ~ + 15 v says [ Logic 0] , 5V～- 15 v [ Logic 1] 。 Using 'single-ended driven' - — Through the data sender [ TD] Output driver level, and to signal to GND for reference point. When using 'single-ended receiving' - — Through the data receiving end [ RD) Enter the reception level and to signal to GND for reference point. RS232 three-wire system - — To achieve [ Point-to-point bidirectional communication] , need three telecommunication lines, the main square of data the sender [ TD] And from the side of the data at the receiving end [ RD) Connected to the main party of data receiving end [ RD) And from the side of the data sender [ TD] Is linked together, the two side of the signal ground [ 接地) Directly connected. Use RS232 the note - — RS232 serial port can not directly connected with RS485 serial port - — Because they are of different electrical standards; Provide all kinds of serial converter on market, must be connected through the converter. And don't charged call waiting serial ports, call waiting until rare end is power off, otherwise easy to damage the serial port.