Weisheng-hardware test questions

Hardware test questions
1. What is the content of kilhov's theorem?
Kikhov's law includes current law and voltage law.
Current law: the algebra and constant of the branch current of all outgoing nodes at any time point in the set total circuit are equal to zero.
Voltage law: in a set-sum circuit, the voltage algebra and the constant are equal to zero at any time and along any loop.
2. Describe the concept of feedback circuit and list their applications.
Feedback is to input the power in the output circuit into the input circuit in the electronic system.
Feedback types include: Negative Feedback of voltage series, negative feedback of current series, negative feedback of voltage series, and negative feedback of current series.
Negative Feedback advantages: reduces the gain sensitivity of the amplifier, changes the input resistance and output resistance, improves the linearity and nonlinear distortion of the amplifier, effectively extends the amplifier's channel band, and automatically adjusts the function.
Negative Voltage Feedback features: the output voltage of the circuit tends to be constant.
Negative current feedback features: the output current of the circuit tends to maintain a constant.
3. Differences between source filter and passive filter
Passive filter: This circuit consists of passive components R, L, and C.
Active Filter: it is integrated with OP-ops and R and C, and has advantages such as no inductance, small size, and light weight.
The open-loop voltage gain and input impedance of the integrated op-amp are both very high, and the output resistance is small. It also plays a certain role in voltage amplification and buffering after forming an active filter circuit. However, the bandwidth of the integrated op-amp is limited, so the current active filter circuit is difficult to work frequently.
Digital Circuit
1. What is the difference between a synchronous circuit and an asynchronous circuit?
Synchronous circuit: The Clock inputs of all triggers in the storage circuit are connected to the same clock pulse source, so the changes in the status of all triggers are synchronized with the added clock pulse signal.
Asynchronous circuit: the circuit does not have a unified clock. Some trigger clock inputs are connected to the clock pulse source, which means the status changes of these triggers are synchronized with the clock pulse, the status changes of other triggers are not synchronized with the clock pulse.
2. What is the logic of "line and"? What are the specific requirements on hardware features for implementing it?
Connect the outputs of two door circuits in parallel to realize the function of logic.
On the hardware, the OC gate is used for implementation, and an upstream resistor is added to the output port.
The logic gate is burned out because the filling current may be too large without an OC gate.
3. Explain setup time and hold time violation, draw a picture, and explain the solution. (Via2003.11.06 Shanghai test questions)
Setup/holdtime is the time requirement between the input signal and the clock signal of the test chip. The creation time refers to the time when the trigger's clock signal remains unchanged before the rising edge. The input signal should arrive at the chip at t time in advance of the clock rising edge (for example, the rising edge is valid), which is the time-setup time. if the setup time is not met, the data cannot be pushed into the trigger by the clock. Only on the rising edge of the next clock can the data be pushed into the trigger.
The holding time refers to the time when the trigger's clock signal remains unchanged after the rising edge. If the hold time is not enough, data cannot be pushed into the trigger.
Setup Time and hold time ). The time when the data signal is created is the time before the clock edge. The retention time refers to the time when the data signal remains unchanged after the clock jumps to the edge. If the duration of the data signal before and after the clock is triggered exceeds the set-up and keep-up time, the excess time is called the set-up time margin and the set-up time margin respectively.
4. What is competition and adventure? How to judge? How to eliminate it? (Hand Wang Written Examination)
In the combination logic, due to different latencies in the input signal path of the door, the inconsistent arrival time is called competition.
Glitch is called adventure. If there is an opposite signal in the Boolean expression, competition and risk-taking may occur.
Solution: one is to add a Boolean elimination item, and the other is to add a capacitor outside the chip.
5. Terms: SRAM, ssram, and SDRAM
SRAM: static RAM
DRAM: Dynamic RAM
Ssram: synchronousstatic Random Access Memory synchronizes static random access memory. It is a type of SRAM. All access to ssram is started along the rise/fall of the clock. Address, data input, and other control signals are related to clock signals. Unlike asynchronous SRAM, asynchronous SRAM access is independent of the clock, and data input and output are controlled by address changes.
SDRAM: synchronousdram synchronous dynamic random memory
6. Differences between FPGA and ASIC. (Unknown)

Answer: FPGA is a programmable ASIC.
ASIC: a dedicated integrated circuit designed and manufactured for a user. According to the specific requirements of a user, it can be customized with low development cost, short delivery cycle supply, and semi-customized IC. And
Compared with other ASIC (Application Specific ic) such as gate arrays, they also have the advantages of short design and development cycles, low design and manufacturing costs, advanced development tools, no testing for standard products, stable quality, and real-time online inspection.
7. What are the differences between OTP film and mask film?
Otpmeans one time program, one-time Programming
Mtpmeans multi time program, Multiple Programming
OTP (one timeprogram) is a memory type of MCU.
MCU memory types can be divided into mask (mask) Rom, OTP (one-time programmable) Rom, flashrom and other types.
Maskrom's MCU is cheap, Program Fixed at factory time, suitable for applications with fixed programs;
The falshrom MCU program can be repeatedly written, which is flexible, but expensive. It is suitable for non-price-sensitive applications or for development purposes;
The MCU price of OTP Rom is between the first two and has a one-time programmable capability. It is suitable for applications that require both flexibility and low cost, in particular, electronic products that require rapid mass production are constantly updated.
8. What should I first check if the single-chip microcomputer is not running after power-on?
First, check whether the power supply voltage is normal. Use a voltmeter to measure the voltage between the grounding pin and the power supply pin to see if it is the power supply voltage, such as the commonly used 5 V.
Next, check whether the reset pin voltage is normal. Measure the voltage values of the reset button and the open reset button to see if they are correct.
Then check whether the crystal oscillator is vibrating. Generally, use an oscilloscope to view the waveform of the crystal oscillator pin. Note that the "x10" file of the oscilloscope probe should be used. Another method is to measure the IO port level in the reset state, hold down the reset key, and then measure the voltage of the IO port (except for the P0 port that is not externally pulled) to check whether it is high, if it is not high, most of the reason is that the crystal oscillator has no vibration.
In addition, it should be noted that if the in-chip Rom is used (in most cases, external Rom expansion is rarely used), the EA pin must be increased, otherwise, the program may run in disorder. Sometimes it is possible to use a simulator, but it is not possible to burn the film. It is often because the EA pin is not high (of course, the crystal oscillator is only one reason ). After the above checks, the fault can be ruled out. If the system is unstable, it is sometimes caused by poor power filtering. A 0.1uf capacitor is attached between the power supply pin and the ground pin of the single chip microcomputer to improve the performance. If the power supply does not have a filter capacitor, a larger filter capacitor is required, for example, 220uf. When the system is unstable, you can try the capacitor (the closer the chip is, the better ).
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