The RS - 232, RS - 422 and RS - 422 standard and application?

RS - 232, RS - 422 and RS - 485 serial data interface standards, first by the electronic industries association (EIA) to formulate and publish.

The RS - 232 is the most widely used in PC computer and communications industry a serial interface. RS - 232 serial communication is defined as a low rate of increase in communication distance of single-ended standards. RS - 232 unbalanced transmission ways, that is, the so-called single-ended communications.

The RS - 422, RS - 485 and RS - 485, the data signal USES the differential transmission mode, also known as the balance transfer, it USES A pair of twisted pair, one line is defined as A, another line is defined as A B.

Usually, send the drive is between A and B level in 2 ~ + 6 + v, is A logical state, negative level in 2 ~ 6 v, is another logical state. Otherwise a signal to the C, in the RS - 485 and a "enable" side, and in the RS - 422 this is optional. "Enabled" is used to control the connected to the transmission line cut and send drives. When the "enable" side effect, send the drive in a high impedance state, known as the "third state", which is different from the logic "1" and "0" the third state.

Due to the RS - 485 from and is based on RS - 422, RS - 485 many similar electric regulation and the RS - 422. Such as using balance transmission mode, all need to take on a transmission line terminating resistance, etc. RS - 485 can be used in a second line and the four lines, two wire can realize true multi-point two-way communication.

The RS - 485 and RS - 422 also is different the common-mode output voltage is different, the RS - 485-7 v to + 12 v, and RS - 422-7 v to + 7 v, RS - 485 receiver minimum input impedance of 12 k? The RS - 422 is 4 k; As a result of the RS - 485 to satisfy all the RS - 422 specification, so the driver of the RS - 485 can be used in the application of RS - 422 network.