Ten Daily Electronic Common Sense-Section 60

What is the ARP protocol?

The TCP/IP protocol suite is divided into four layers, and different hosts in the Internet are addressed by using different IP addresses through the IP layer. That is to say, the IP address is used in the IP layer and its upper layer, which is a logical address (Logic Address). However, only after the datagram of the IP layer is transmitted to the data link layer, can the IP datagram be transmitted to the destination host or a router closer to the destination host through the network interface card of the data link layer.
The data frame transmitted at the data link layer can only identify the physical address of the network card, and the commonly used Ethernet is the 48-bit MAC address. There is a problem in this way, when an IP datagram is transmitted from a host to a direct connection with it (the direct connection is mentioned here because the IP datagram is transmitted from the source host station by station through point-to-point communication during the transmission process. To the destination host, when the stations passing in the middle are mainly routers or hosts with router functions), how does the source host obtain the physical address of the other host?  
The TCP/IP protocol suite has specially designed a protocol for address resolution, the Address Resolution Protocol, which can map an IP address to a corresponding physical address. In addition, for hosts that cannot save IP addresses (such as diskless workstations), the TCP/IP protocol suite also provides a Reverse Address Resolution Protocol that maps from physical addresses to IP addresses.

What fields are included in each transport layer PDU?

1. A transmission byte to ensure end-to-end data transmission;
2. Device status and extended device status bytes;
3. One or more HART commands.

What are the characteristics of low frequency and high frequency RFID antennas?

1. The antennas are all in the form of coils;
2. The coils have various forms, which can be circular rings or rectangular rings;
3. The size of the antenna is much larger than that of the chip, and the size of the electronic tag is mainly composed of determined by the antenna;
4. The substrates of some antennas are soft and suitable for sticking on the surface of various objects;
5. Electronic tags composed of antennas and chips can be smaller than a thumb and can be mass-produced on strips.

What are the reset sources for the LPC2000 series ARM?

LPC2000 series ARM has 2 reset sources, external reset and watchdog reset.

What constitutes the structure of a short frame?

It consists of start bit S, 7-bit data bits bl-b7 and communication end bit E.

What is an ASIC?

ASIC (Application Specific Integrated Circuits (ICs)s) refers to integrated circuits designed and manufactured in response to specific user requirements and the needs of specific electronic systems. Currently, it is one of the most popular ways to use CPLD (Complex Programmable Logic Device) and FPGA (Field Programmable Logic Array) to design ASIC. Their commonality is that they all have user field programmable features and support boundary scan technology. But the two have their own characteristics in terms of integration, speed and programming.

What is the difference between blocking assignment and non-blocking assignment?

The basic difference between blocking assignment and non-blocking assignment is that blocking assignment executes statements sequentially, while non-blocking assignment executes statements in parallel. The meaning of the two sentences is different, and the application of modeling is also different.

What are the main technical parameters of thyristors?

There are two main technical parameters of thyristor: rated forward average current and reverse blocking peak voltage.  

1. Front foot forward average current/F: It refers to the average value of the power frequency sinusoidal current passing between the cathode and the anode under the conditions of the specified ambient temperature, standard heat dissipation and full conduction. /F=0.6371, where I is the effective value of the sinusoidal current.  
2. Reverse blocking peak voltage: It refers to the reverse peak voltage that is allowed to be repeatedly applied to the device when the control pole is open and the junction temperature is rated, and it is 80% of the maximum reverse test voltage as specified.

What are the factors that affect the magnitude of the zero-sequence current flowing through the protection?

1. The magnitude of the zero-sequence current is related to the type of ground fault.
2. The magnitude of the zero-sequence current is not only related to the zero-sequence impedance, but also to the positive and negative sequence impedances.
3. The magnitude of the zero-sequence current is closely related to the number of transformers that protect the neutral point of the system behind and the opposite system.
4. The magnitude of the zero-sequence current is related to the distance of the short-circuit point.

What are the functions of intelligent sensors?

• Intelligent sensors generally have the following functions:
  1. It can make judgments and decisions based on the detected signals.
  2. Corresponding operations can be performed according to software control.
  3. With input and output interfaces, it can exchange information with the outside.
  4. It has the functions of self-detection, self-correction and self-protection.