Introduction to RS-232 protocol Serial Interface Standard

RS-232 protocol, in learning the principles of the Microcomputer should have friends have contact. This Protocol is primarily a standard for serial interfaces. Therefore, there should be more hardware knowledge. Next we will give a brief introduction to the content of this Protocol.

RS-232 is the serial data interface standard, initially developed and released by the Electronic Industry Association EIA), The RS-232 protocol was released in 1962, named as EIA-232-E, as the industrial standard, to ensure compatibility between products of different manufacturers. RS-422 from the Development of RS-232, it is to make up for the lack of RS-232 and proposed.

In order to improve the shortcomings of short distance and low rate of RS-232 communication, a balanced communication interface is defined in RS-422 to increase the transmission rate to 10 Mb/s, transmission Distance extended to 4000 feet speed lower than kb/s), and allows a maximum of 10 receivers to be connected on a balanced bus. RS-422 is a kind of single-machine transmission, multi-machine receive one-way, balanced transmission specification, named as TIA/EIA-422-A standard.

In order to expand the scope of application, EIA also established RS-422 standards on the basis of RS-485 in 1983, added multi-point, two-way communication capability, that is, allow multiple transmitters to connect to the same bus, at the same time, the driving capability and conflict protection characteristics of the transmitter are added, and the common mode range of the bus is extended, which is named TIA/EIA-485-A standard.

Since the proposed standards proposed by EIA are prefixed with "RS", the above standards are still used to the RS prefix in the communication industry.

RS-232, RS-422 and RS-485 standards only regulate the electrical characteristics of the interface, and do not involve connectors, cables or protocols, on the basis of which users can establish their own high-level communication protocol. Therefore, in the video industry, many manufacturers have established a set of high-level communication protocols, either open or exclusively used by manufacturers. For example, the recorder manufacturers Sony and Panasonic on the video recorder RS-422 control protocol is different, Video Server Control Protocol is more, such as Louth, Odetis Protocol is open, proLINK is based on Profile.

Serial Interface Standard for RS-232 Protocol

At present, RS-232 is one of the most widely used serial interfaces in PC and communication industry. A RS-232 is defined as a single-ended standard that increases communication distances in low-rate serial communication. The RS-232 adopts the unbalanced transmission mode, that is, the so-called single-ended communication.

The data signal sent and received is relative to the signal location, for example, the data sent from the DTE device is 2-pin relative to 7-pin signal location when using the DB25 connector, for the definition of DB25 pins, see Figure 1. Typical RS-232 signals swing between positive and negative levels, while sending data, the sender drive outputs positive and negative flat at + 5 ~ + 15 V. The negative value ranges from-5 ~ -15 V level. When there is no data transfer, the online is TTL, from the beginning to the end of the data transfer, the online level from the TTL level to the RS-232 protocol level and then return the TTL level. The typical operating level of the receiver is + 3 ~ + 12 V and-3 ~ -12 V.

Because the difference between the transmission level and the receiving level is only 2 V to 3 V, the common mode suppression capability is poor. In addition, the distribution capacitor on the twisted pair wires can provide a maximum transfer distance of about 15 meters, the maximum speed is 20 kb/s. RS-232 is for point-to-point that only one pair of receiving, sending equipment) Communication Design, its drive load is 3 ~ 7kb. So RS-232 is suitable for communication between local devices.

RS-232 protocol is the interface standard between DTE and DCE, as dce modem and as DTE computer connection.