After analyzing the similarities and differences with the RS-485 bus CAN portion hesitant to PCA82C250 interface circuit presents an example CAN bus communication with physical layer interface circuitry instead of RS-485 bus interface circuit connected directly communicate with the microcontroller Network design, which can form a high-performance, low-cost, data communication safe and reliable distributed measurement and control system. 1 Overview The current loop form has basically withdrawn from the historical stage due to reasons such as more complicated wiring than the RS-485 / RS-422 bus form. The RS-485 bus wiring form has fewer two-pole communication lines than the RS-422 bus wiring form and the anti-interference ability is enhanced, thereby making the wiring form simpler and cheaper. Therefore, the RS-485 bus basically dominates the single-chip computer It is the application of the communication physical layer of the distributed multi-machine measurement and control system at the core. However, with the development of science and technology, the bus efficiency of RS-485 bus is low, the real-time performance of the system is poor, the reliability of communication is low, the maintenance cost is high in the later period, the network engineering is complicated to debug, the transmission distance is not ideal, the single bus can be connected with fewer nodes, and the application is not Shortcomings such as flexibility are slowly exposed. Therefore, there is an urgent need to find a new, simple and effective communication physical layer interface chip to replace the RS-485 bus physical layer interface circuit for network communication, which improves the distribution of multi-machine interconnection. The reliability of the measurement and control system is of great significance. Compared with other fieldbuses, the CAN department has hesitant advantages in terms of communication capability, reliability, real-time performance, flexibility, ease of use, transmission distance and cost, and has become the most promising fieldbus in the field of control. one. For the physical layer interface of the CAN bus, most of the existing CAN bus communication networks are formed by connecting the CAN bus physical layer interface circuit and the CAN bus controller. The author's in-depth analysis and practice have proved that the CAN bus physical layer interface circuit (in accordance with ISO11898 standard) can also be directly connected with the single-chip microcomputer to form a highly reliable, low-cost, simple and practical, multi-machine interconnected distributed measurement and control system. 2 Comparison of CAN and RS-485 physical layer characteristics The CAN bus has a dedicated interface circuit at the physical layer, which has characteristics. The similarities between the physical characteristics of the CAN bus and the RS-485 bus are: · Two-wire system, half-duplex serial communication; · Differential transmission, balanced reception; · The transmission medium is twisted pair; · Need terminal matching resistor; · The communication circuit can work under the condition of 5V power supply. Compared with the RS-485 bus, the CAN bus communication physical layer interface circuit (take PCA82C250 as an example) has the following advantages: · Comply with ISO11898 international standard; Long data transmission distance (up to 10km / 5kb / s); High data transmission rate (up to 1Mb / s / 40m); · The bus value in the CAN bus is two complementary logic "dominant" or "recessive" bit values; · Can realize multi-master communication network design, the signal can be achieved through the "wire and" on the bus to achieve non-destructive bus arbitration; · No sending and receiving conversion control pins; · With anti-momentary pulse interference (-150V · It has higher bus voltage (-8V ～ + 18V) endurance than RS-485 bus; · Slope control of sending pulses to reduce radio frequency interference; Differential receivers can resist a wide range of common mode interference; · Short circuit protection between bus and power and ground; · With anti-bus short circuit protection ability; Under certain single-line conditions, it can still protect the normal operation of the bus; · With low current standby mode; · Bus is equipped with a resistor network inside, without external upper and lower resistors; The unpowered nodes have no effect on the bus; · At least 110 nodes can be connected. It can be seen that the use of a dedicated interface circuit for the physical layer of the CAN bus instead of the RS-485 bus interface circuit to form a mixed mode multi-machine interconnection distributed measurement and control system communication network can overcome the inherent defects of the RS-485 bus and make full use of CAN The advantages of the bus physical layer can construct a very competitive distributed measurement and control system in a simple form, at a lower price and with higher performance.
1. offer a comfortable environment in living place
2. the extra decoration while turn-off situation
3. instant start, no speckle, no flickering, no humming
Whether you are looking for the best LED desk lamp for college or an Adjustable LED Table Lamp for next to your sofa,
you are sure to find a lamp to fit your needs at Superlight.
LED Desk Lamp With Digital Clock LED Desk Lamp With Digital Clock Shenzhen Superlight Technology Co., Ltd. , https://www.superlighttech.com