Serial communication method
2.1 Full-duplex and half-duplex modes
If a data communication system uses different paths for the two transmission directions of data, such a system can work in full-duplex mode, and a system using full-duplex mode can send and receive at the same time. Corresponding to the full-duplex mode is the half-duplex mode. In the half-duplex mode, input and output use the same channel. Computer serial communication uses the full-duplex mode.
2.2 Synchronous communication and asynchronous communication
Serial communication can be divided into two types, one is called synchronous communication, and the other is called asynchronous communication. When using synchronous communication, many characters are composed into an information group, so that the characters can be transmitted one after another. However, in each group A synchronization character must be added at the beginning of the information (usually called an information frame). When there is no information to be transmitted, a blank character must be filled in, because synchronization transmission does not allow for gaps. using asynchronous communication, the transmission distance between two characters is arbitrary, so some flags must be used as separators before and after each character.
In comparison, synchronous communication requires both parties to communicate at the same rate and to coordinate accurately. It ensures that the sender and receiver are accurately synchronized by sharing a single clock or timing pulse source. Its characteristic is that it allows sending a sequence of characters , each character has the same number of data bits, no start bits and stop bits, and is highly efficient. Synchronous communication is transmitted in units of multi-byte data blocks, and an identification sequence is added before the data block to form a frame . Synchronization methods are divided into two types: byte synchronization and bit synchronization, and the latter method is usually used.
Asynchronous communication does not require synchronization between both parties, and the sender and receiver can use their own clock sources. The two parties do not follow the asynchronous communication protocol, using characters as data transmission units, and the time interval at which the sender transmits characters is uncertain. Each character transmission starts with a start bit and ends with a stop bit. The number of data bits, parity check method and stop number of characters specified by both communicating parties must be the same. The transmission efficiency is lower than the synchronous communication method, and the cost is also low. Asynchronous communication is in character units and has a length of 5-8 bits.
What is a serial port?
Before each data byte, the serial port sends a start bit, which is a single bit with a value of 0. After each data byte, it sends a stop bit to indicate that the byte is complete. It can also send parity bits.
Serial ports, also called communications (COM) ports, are bidirectional. Two-way communication allows each device to receive and send data. Serial devices (such as serial servers) use different pins to receive and transmit data – using the same pins limits communication to half-duplex, meaning information can only travel in one direction at a time. Using different pins allows for full-duplex communication, where information can travel in both directions at once.
Serial ports rely on a special controller chip called a Universal Asynchronous Receiver/Transmitter (UART) to function properly. The UART chip takes the parallel output of the computer system bus and converts it into serial form for transmission through the serial port. To run faster , most UART chips have built-in buffers of 16 to 64 KB. This buffer allows the chip to buffer incoming data from the system bus while processing data output to the serial port. Most standard serial ports have a maximum transfer rate of 115 Kbps ( kilobits per second), while high-speed serial ports, such as Enhanced Serial Port (ESP) and Super Enhanced Serial Port (Super ESP), can reach Data transfer rate of 460 Kbps.
9-pin serial interface description:
● Carrier detection: Determine whether the modem is connected to a working phone line.
● Receive data: The computer receives information sent from the modem.
● Transmitting data: The computer sends information to the modem.
● Data terminal ready: The computer tells the modem that it is ready to talk.
● Signal ground: pin ground.
● Data set ready: The modem tells the computer that it is ready to talk.
● Request to Send: The computer asks the modem if it can send the message.
● Clear to Send: The modem tells the computer that it can send information.
● Ring indicator: After a call is placed, the computer acknowledges a signal (sent from the modem) indicating that a ring has been detected.
Is het principe van seriële communicatie gebaseerd op flow control?
An important aspect of serial communications is the concept of flow control. This is the ability of one device to tell another device to temporarily stop sending data. Flow control is enabled using Command Request to Send (RTS), Clear to Send (CTS), Data Terminal Ready (DTR), and Data Set Ready (DSR).
Let’s look at an example of how flow control works: You have a modem communicating at 56 Kbps. The serial connection between your computer and modem transfers at 115 Kbps, twice as fast as before. This means that the modem is getting more data from the computer than it can transmit over the phone line. Even if the modem has a 128K buffer for storing data, it will quickly run out of buffer space and not function properly with all data streams.
Using flow control, the modem can stop the flow of data from the computer before it overflows the modem buffer. The computer keeps sending a signal on the “send request” pin and checking for a signal on the “clear to send” pin. If there is no Clear to Send response, the computer will stop sending data and wait for a Clear to Send before resuming. This allows the modem to keep the data flow running smoothly.
Introduction to the production of serial communication product RS232
During the product development period, the demand for product crystals is estimated based on market research and analysis. When the demand for the product is determined, the investment analysis of the production line begins. For some products with a short cycle, the production line needs to be short and efficient from design to construction, which is relatively tight; while for some products with a long cycle and large output, the production line often requires a higher degree of automation to reduce personnel investment, etc.; therefore The design of the The production line is based on the product and refers to the market demand and available investment funds to determine the capital investment of the production line, determine the operation mode of the production line (manual, semi-automatic or fully automatic), and the basic design requirements of the production line.
The layout of the general production line is roughly divided into the production line body part, the product raw material area part, and the product finished product area part. If the product qualification rate is low, some factories also set up a rework area; here we mainly introduce the line body part of the production line: small electrical products are used as the For example, the body part of the production line can generally be divided into product assembly, product testing, and product packaging: product assembly includes auxiliary fixtures, one-piece batches, pliers, and electric batches.
Each work station has corresponding work instructions. Workers must strictly follow the work instructions to avoid errors. Most electrical products require one or more tests. Only after passing the test can they be packaged and shipped. Therefore, The configuration and design of test equipment is the core part of technology in production line design and is also a key investment part of the production line. Finally, basic production lines have packaging stations. The packaging station can be very simple to implement, but it may be more complicated depending on the product . Simple ones are generally only packed manually; while complex packaging stations may require each product to have a corresponding product serial number, corresponding packaging label, etc. In order for all numbers to correspond, the poultry must be automated to avoid manual errors. Or use a barcode scanner to scan the barcode of a single product and get the corresponding label after scanning. The operation process is relatively complicated.
Trefwoorden: seriële poort server