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  • Ten Daily Electronic Common Sense-Section 57

    What are the main features of VHDL?

    1. As the first international standard of HDL, VHDL has strong portability.
    2. With rich simulation statements and library functions, the design can be simulated at any time, so the errors in the design can be eliminated before the circuit system assembly, and the feasibility of the design system function can be checked in the early stage of the design. Strong predictive ability.
    3. VHDL has good readability, close to high-level language and easy to understand.
    4. The system design has nothing to do with the hardware structure, which facilitates the conversion of the process, and will not make the description outdated due to the process change.
    5. Supporting modular design, large-scale design projects can be decomposed into several small projects, and existing design projects can be called as a module.
    6. For a definite design completed with VHDL, EDA tools can be used for logic synthesis and optimization, and the VHDL description can be automatically converted into a gate-level netlist file.
    7. The design is flexible, the modification is convenient, and the communication, preservation and reuse of the design results are also convenient, and the product development speed is fast and the cost is low.

    What is an optical encoder sensor?

    The optical encoder sensor is a conversion device that converts the measured angular displacement into an electrical signal expressed in the form of a digital code by photoelectric method.

    What are the interrupt considerations?

    1. Read the 00000h address unit: Do not read the 00000h address in the program. When accepting the interrupt request of the maskable interrupt, the CPU reads the interrupt information (interrupt number and interrupt request level) in the interrupt response sequence from the 00000h address. At this time, the IR bit of the accepted interrupt is “0”. If the address 00000h is read in the program, the IR bit of the interrupt with the highest priority among the enabled interrupts is “0”. At this point, it is possible to cancel the interrupt or generate an unexpected interrupt request.
    2. SP setting: Before accepting the interrupt, a value must be set for SP (USP, ISP). After reset, SP(UsP, ISP) is “0000h”. Therefore, if an interrupt is accepted before setting values ​​for SP (USP, ISP), the program may run away. Especially when using the NMl interrupt, the ISP must be set at the beginning of the program. For the l instructions that start after reset, no interruption can be generated, including NM1 interruption.
    3. NMl interrupt: NMl interrupt cannot be disabled. When not in use, the NMl pin must be connected to VCCl through a pull-up resistor. By reading the P8 5 bits of the P8 register, the value of the NMl pin can be read. The P8 5 bit can only be read when the level of the pin is judged in the NMl interrupt program. When the NMl pin is at “L” level, it cannot transition to stop mode. Because when the NM1 pin is “L” level, the CM10 bit of the CM1 register is fixed as “0”, and the channel entering the stop mode is turned off. When the NMl pin is at “L” level, it cannot switch to the standby mode. If the NMl pin is “L” level, ‘even if the CPU stops running, the CPU clock does not stop, so the power consumption cannot be reduced. In this case, the CPU will return normally through the interrupt generated thereafter. The “L” level and “H” level width of the signal input to the NM1 pin must be maintained at more than 300ns in 2 cycles of the CPU clock.
    4. Change of interrupt source: If the interrupt source is changed, the IR bit of the interrupt control register may be “1” (there is an interrupt request). So when using the interrupt, the lR bit must be cleared to “0” (no interrupt request) after changing the interrupt source. The interrupt source change mentioned here includes all elements of changing the interrupt source, polarity, and timing assigned to each software interrupt number. Therefore, when changing the mode of the peripheral function related to the interrupt source, polarity, and timing, be sure to clear the IR bit to “0” (no interrupt request) after changing these contents.

    What are the relay transmission strategies in the two-way relay system?

    The first is the traditional four-slot relay strategy;
    The second is the link layer network coding relay strategy;
    The third is the physical layer network coding PNC relay strategy. The third strategy is also called a Denoise-and Forward (DAF) relay strategy.

    What are the factors that influence the design?What are the important factors?

    • Factors that affect the design include the usual cost, size, weight, etc. Other important factors are:
      1. When a device with an exhausted battery is plugged into the USB port, how long does it take to start full-featured operation.
      2. Allow battery charging time.
      3. Power distribution within the USB power limit.
      4. Do you need an AC adapter for charging?

    How to measure the quality of a diode

    Put the multimeter on the R×100 or R×1 block, connect one end of the diode with the red test lead, and the other end with the black test lead. Take a look at where the multimeter is left, and note the resistance value at this point. Then adjust the diode, connect it to the two test leads of the multimeter, and check the resistance value again.
    In the two tests, if the resistance value is large once and the resistance value is small once, it means that the diode has a unidirectional conduction effect. The diode is good. And it can be seen that the one with the small resistance value and the end connected with the black test lead is the anode of the diode.
    If the pointer of the multimeter swings too much between the two measurements, the diode is broken down. If the resistance is particularly small, the diode is broken.
    If you want to measure whether the diode is a silicon tube or a germanium tube, you can use the above method to measure the quality of the diode. Measure the forward resistance of the diode (the smallest resistance of the two measurements is the forward resistance).
    If the forward resistance of the diode is measured between 500Ω and 1K with a multimeter R×100 block, it is a germanium tube. If the measured forward resistance is between several thousand ohms and tens of thousands of ohms, it is a silicon tube.

    What is the substrate modulation effect?

    The substrate modulation effect is called the body effect or the back gate effect. In the analysis of the previous section, the source and the substrate are shorted together to make VBS=0. When the potentials of the source and the substrate are not equal, it will affect the performance of the MOS transistor. 
    In CMOS integrated circuits, in order to keep the devices in an isolated state from each other, the PN junctions between the substrate and the source and drain regions of each tube should be in reverse bias. Generally, the P-type substrate of the NMOS transistor is connected to the lowest potential in the circuit, and the N-type substrate of the PMOS transistor is connected to the highest potential of the circuit. Therefore, for NMOS transistors, VBS≤0; for PMOS transistors, VBS≥0. In some cases, VBS=0 cannot be guaranteed.
    Under a certain V∽, the amount of charge induced on the surface of the substrate is certain. A part of the induced charge is used to form the depletion layer, and the other part is used to form the channel. When the substrate potential of the NMOS transistor becomes negative, the depletion layer between the channel and the substrate becomes thicker.
    That is, at the original threshold voltage, since the depletion layer consumes more induced charges, the remaining charges are not enough to form the channel. A higher gate-to-source voltage is required to form the channel, so the threshold voltage is raised. For the channel formed by a certain VGS, the channel is narrowed due to the thickening of the depletion layer, which reduces the drain current ID.

    What are the 8-bit HCS08 central processing units (CPUs)?

    • 40MHzHCS08 CPU (20MHz bus).
    • HC08 instruction set with additional BGND instruction.
    • Support up to 32 interrupt/reset sources.

    What are the characteristics of the register VHDL language?

    Compared with other hardware description languages, VHDL has many unique features in the description of sequential circuits. The most obvious is that VHDL mainly describes the function and logic behavior of sequential devices rather than the structure. It enables the computer to synthesize sequential circuits that meet the requirements, thus fully embodying the powerful function of VHDL circuit system behavior description.

    What are the advantages of the MC68HC05SC series chip smart card?

    1. Improve data security.
    2. Application flexibility.
    3. Verification of the legitimacy of applications and transactions.
    4. The price is compensated by validity.
    5. Multi-application capability.
    6. Offline capability.


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