Ethereum leveldb

1. At the top of Ethereum is DAPP. It exchanges with the smart contract layer through Web3. JS. All smart contracts run on EVM (Ethereum virtual machine) and use RPC calls. Below EVM and RPC are the four core contents of Ethereum, including: blockchain, consensus algorithm, mining and network layer. Except DAPP, all other parts are in the Ethereum client. The most popular Ethereum client is geth (go Ethereum)

2. Blockchain technology service refers to the use of blockchain technology to build a new blockchain to replace the traditional Internet architecture services. At present, in the field of blockchain, hyperledger, multichain, Ethereum private chain and other frameworks are mainly used to build multiple instances to solve the problems that have been proved to be well solved by using traditional Internet technology, commonly known as "forced blockchain". These applications also have typical characteristics. We hope to build our own blockchain system. In fact, it is more appropriate to call it distributed ledger technology
in this case, a better technology stack is recommended: pingcap / tidb, or distributed database based on pbft protocol, rather than private blockchain system. Therefore, the blockchain technology service is called bats
the Xueshuo innovation blockchain Technology Workstation of Lianqiao ecation online is the only approved "blockchain Technology Specialty" pilot workstation of "smart learning workshop 2020 Xueshuo innovation workstation" launched by the school planning, construction and development center of the Ministry of ecation of China. Based on providing diversified growth paths for students, the professional station promotes the reform of the training mode of the combination of professional degree research, proction, learning and research, and constructs the applied and compound talent training system.

3. Now the first grade ore bars are all 800, so mining is good. If you are below 35, you can sell 275 magic stones. If you are tall, go to golden Cologne. Then 60 below in Cancun fight earn dead, I am like that

4.

MPI / DP / PPI are all based on RS485 network, the difference is that the communication protocol used is different, and the application place is also different. MPI / DP for 300 / 400, PPI for 200

MPI is used for short communication distance and small amount of data,
it is generally used for connection programming PG, field OP, master-slave communication, DP is generally used for master-slave communication and field level real-time communication,
the communication rate is high

the difference between DP port and MPI port depends on the CPU used. If the 9-pin DP port represented on the CPU is MPI / DP, then this port can be configured as DP port or MPI port by hardware. If it is only represented as MPI port, then it can only be used as MPI port
and DP port can only be used as DP port

RS485 and RS232 are all serial ports,

RS232: the RS232 interface connector uses a 25 core plug socket of db-25. The RS-232 interface between some equipment and PC does not use the other party's transmission control signal, so only three interface lines are needed, namely "send data", "receive data" and "signal ground". Therefore, DB-9 core plug socket is adopted, and shielded twisted pair is adopted for transmission line

RS485: RS485 has no specific physical shape, and the interface is adopted according to the actual situation of the project

MODBUS is a serial communication protocol, which is a common connection mode between instrial electronic devices. Including ASCII, RTU, TCP and so on, there is no physical layer. The physical interface of Modbus communication can be serial port (including RS232 and RS485) or Ethernet port

its communication follows the following process:

1. The master device sends a request to the slave device

2. The slave device analyzes and processes the request of the master device, and then sends the result to the master device

3. If there is any error, the slave device will return an abnormal function code

Due to the early appearance of RS232 interface standard, it is inevitable to have some shortcomings, mainly including the following four points:

1. The signal level value of the interface is high, which is easy to damage the chip of the interface circuit, and it is not compatible with TTL level, so it is necessary to use level conversion circuit to connect with TTL circuit

In asynchronous transmission, the baud rate is 20kbps

The interface uses a signal line and a signal return line to form a common ground transmission form, which is easy to proce common mode interference, so the anti noise interference is weak

The standard value of the maximum transmission distance is 50 feet, which can only be used for about 50 meters

In view of the deficiency of RS232 interface, some new interface standards have appeared continuously, and RS-485 is one of them, which has the following characteristics:

1, the electrical characteristics of RS-485: Logic "1" is represented by the voltage difference between two wires as + (2-6) V; Logic "0" is represented by - (2-6) V voltage difference between two lines. The interface signal level is lower than RS-232, so it is not easy to damage the chip of interface circuit, and the level is compatible with TTL level, so it is convenient to connect with TTL circuit

The maximum data transmission rate of RS-485 is 10Mbps

The RS-485 interface is a combination of balanced driver and differential receiver, which enhances the ability of anti common mode interference, that is, good anti noise interference

The standard maximum transmission distance of RS-485 interface is 4000 feet, which can reach 3000 meters. In addition, only one transceiver can be connected to RS-232 interface on the bus, that is, single station capacity. The RS-485 interface allows up to 128 transceivers to be connected on the bus. That is to say, it has the ability of multi station, so that users can use a single RS-485 interface to establish the equipment network conveniently

5. Configuration software to read MDB and other data content have relevant settings, according to the settings can be! It's not very complicated

6. The transmission delay in Ethernet is related to the connecting devices, transmission media and network interconnection devices experienced from the source to the target

7. It's like the intensity of the signal

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9. 10m / s --- this is the unit of data transmission rate< According to Shannon's theorem, the relationship between data transmission rate Rmax and channel bandwidth B and signal-to-noise ratio S / N is as follows:

Rmax = b.log2 (1 + S / N)

where Rmax is in BPs, bandwidth B is in HZ, and signal-to-noise ratio S / N is usually expressed in dB. If s / N = 30 (DB), then according to the formula:

s / N (DB) = 10. LG (s / N)

s / N = 1000

if bandwidth B = 3000hz, Rmax ≈ 30kbps.

10. Information security or data security has two opposite meanings: one is the security of data itself, which mainly refers to the active protection of data by using modern cryptographic algorithms, such as data confidentiality, data integrity, two-way strong identity authentication, etc.; the other is the security of data protection, which mainly refers to the active protection of data by using modern information storage means, such as through disk array, data security, etc Data backup, remote disaster recovery and other means to ensure the security of data, data security is an active inclusion measures, the security of data itself must be based on reliable encryption algorithm and security system, mainly symmetric algorithm and public key cryptosystem
the security of data processing refers to how to effectively prevent database damage or data loss caused by hardware failure, power failure, crash, human error operation, program defects, viruses or hackers ring data entry, processing, statistics or printing. Some sensitive or confidential data may not be read by qualified personnel or operators, And cause data leakage and other consequences
the security of data storage refers to the readability of the database outside the operation of the system. A standard access database can be opened, read or modified by computer personnel who know a little about some basic methods. Once the database is stolen, even if there is no original system program, you can still write another program to view or modify the stolen database. From this point of view, an unencrypted database is not secure and easy to cause commercial leakage. This involves the confidentiality, security and software protection of computer network communication
basic characteristics of information security
confidentiality, also known as confidentiality, refers to the fact that the information of an indivial or group is not obtained by others who should not be obtained. In the computer, many software, including email software, web browser, etc., have confidentiality related settings to maintain the confidentiality of user information. In addition, spy files or hackers may cause confidentiality problems

integrity
data integrity is one of the three basic points of information security, which means that in the process of transmitting and storing information or data, to ensure that information or data is not tampered with without authorization or can be found quickly after tampering. In the field of information security, it is often confused with confidentiality boundary. Taking RSA encryption of numerical information as an example, hackers or malicious users can change the value of numerical information by performing linear operation on the ciphertext without obtaining the key to crack the ciphertext. For example, if the transaction amount is x yuan, the transaction amount can be 2x by multiplying the ciphertext by 2. Also known as malleability. In order to solve the above problems, we usually use digital signature or hash function to protect the ciphertext

availability
data availability is a user-centered design concept. The focus of usability design is to make the proct design meet the habits and needs of users. Taking the design of Internet website as an example, we hope that users will not feel pressure or frustration in the process of browsing, and that users can use the website function with the least effort to play the maximum efficiency
for this reason, any violation of the "availability" of information is a violation of information security regulations. Therefore, many countries in the world, whether the United States or China, have a campaign to maintain the unrestricted flow of information
the understanding of information security has gone through four stages: data security stage (emphasis on confidential communication), network information security era (emphasis on network environment) and information assurance era (emphasis on four links: protection detection response recovery instead of passive protection)
the main factors that threaten data security
there are many factors that threaten data security, mainly the following are more common:
(1) hard disk drive damage
physical damage of a hard disk drive means data loss. The operation loss, storage medium failure, operation environment and man-made damage of the device can affect the hard disk drive device
(2) human error
e to misoperation, users may delete important files of the system by mistake, or modify parameters that affect the operation of the system, as well as system downtime caused by failure to comply with the specified requirements or improper operation
(3) hackers
here, intruders remotely invade the system through the network, and the intrusion forms include many: system vulnerabilities, (4) the computer system is damaged e to the infection of computer virus, resulting in heavy economic losses. Computer virus has strong replication ability and strong infectivity, especially in the network environment, which spreads faster
(5) information theft
, delete information from the computer or steal the computer altogether
(6) natural disaster
(7) power failure
power supply system failure, an instantaneous overload of electric power will damage the data on the hard disk or storage device
(8) magnetic interference
magnetic interference refers to the important data contact with magnetic material, Will cause computer data to be destroyed