Java Serial port Communication Technology Overview

Serial Communication Overview

There are many kinds of serial communication protocols, such as rs232,rs485,rs422, even the popular USB is serial communication protocol. And the application of serial communication technology is everywhere. Perhaps everybody sees most is the computer serial port and the modem communication. Remember when the PC was first popular in China (about five years before the 90 's), when someone even used a serial line to share data between two computers. In addition to these, the mobile phone, Pda,usb mouse, keyboard, etc. are connected to the computer in the way of serial communication. And the author of the nature of the relationship, the contact is more, like many serial cards, all kinds of serial communication interface with the detection and measurement instruments, serial communication network equipment.

Although there are many kinds of serial communication, but I know the whole electronic communication products, the most RS232 communication methods. Although the USB interface of electronic products are endless, but to understand the Java in the serial communication technology is also necessary, perhaps a reader who would like to use this technology to write a PDA and computer data sharing program.

This article mainly to RS232 to explain the Java serial communication technology.

RS232 Communication Basics

Rs-232-c (also known as EIA Rs-232-c, hereinafter referred to as RS232) is a standard for serial communications developed in 1970 by the United States Electronics Association (EIA) Joint Bell System, modem manufacturers and computer terminal manufacturers. RS232 is a Full-duplex communication protocol that can receive and send data at the same time. There are usually two types of RS232 ports: 9-pin (DB9) and 25-pin (DB25).

Common PIN definitions for DB9 and DB25

Figure 1

A common sideline approach

A common form of communication is a three-wire approach, which connects the sender (TXD) and the receiver (RXD) and the grounding (GND) of two RS232 devices to the connections that many readers know:

Figure 2

In this way, the 2--3,3---2,5 (7)---5 (7) Pins of the RS232 interface between the two ends are connected respectively. 2 of which is the data receiving line (RXD), 3 is the data transmission line (TXD), 5 (7) is grounded (RND). If you have a desktop PC and a notebook computer, you can connect it in this way. The three-wire type can be used to connect most of the RS232 devices. But if you do, you're dead. 2--3,3--2,5 (7)--5 (7) Docking this reason will find that it does not work in connection with some RS232 devices. This is because some of the equipment within the circuit has been 2 and 3 lines, you just 2,3,5 (7) A pair of pins should be on the line.