Ten Daily Electronic Common Sense-Section 30

What are the corresponding functions of the MAC layer?

• It can be roughly divided into the following three:
  1. Multiple access
  2. Resource sharing
  3. Transmission control

What are the components of the Motorola MC68HC08 family of microcontroller clock generator modules?

1. Crystal oscillator circuit (OSC) This circuit generates a highly stable clock signal CGMXCLK through an external quartz or ceramic oscillator. This clock signal is directly output to the time base module and A/D converter, and also to the reference clock. Selection circuit and PLL.
2. Phase-locked loop frequency synthesizer (PLL) The PLL circuit generates the CGMVCLK clock signal and outputs it to the reference clock selection circuit, whose frequency can be controlled by software programming.
3. Reference clock selection circuit The output signal CGMOUT of the clock generator module has two sources: directly use the CGMXCLK signal generated by the crystal oscillator circuit to divide the frequency by 2, or use the CGMVCLK signal generated by the PLL to divide the frequency by 2. The signal output by the clock generator module is divided by 2 as the system bus clock, that is to say, the system bus frequency is 1/4 of the clock signal source frequency CGMXCLK or CGMVCLK.

How do I set the RBLE bit in the corresponding memory bank configuration register?

When performing write access to the external memory bank, the RBLE bit determines whether the WE signal is valid (active low); when performing read access to the external memory bank, the RBLE bit determines whether the BLSn signal is valid (active low).

What are the PLD connection methods?

PLD has 3 connection methods: fixed connection, programming connection, and no connection.

What is the scope of the interrupted timer?

The routines described are for the TMS320F28027 chip, not tested for other models or packages.

What are the precautions for distributed power supply design?

1. Minimize the types of power sources.
2. Minimize the voltage difference between the input voltage and the output voltage of the power conversion module.
3. Leave a certain margin.
4. Try to adopt a distributed scheme by function.
5. Try to shorten the distance between the load and the power supply.
6. The reliability of the power module.
7. Derating design.
8. The operating temperature of the power module.
9. The volume of the power module.

What should be paid attention to when designing a power supply for LEDs?

1. LED is a unidirectional conductive device. Due to this feature, it is necessary to use DC current or unidirectional pulse current to supply power to the LED.
2. LED is a semiconductor device with a PN junction structure, which has a potential barrier electromotive force, which forms a turn-on threshold voltage, and the LED will be fully turned on when the voltage value applied to the LED exceeds this threshold voltage. The threshold voltage of high-power LED is generally above 2.5V, and the tube voltage drop during normal operation is 3~4V.
3. The current-voltage characteristics of the LED are non-linear, and the current flowing through the LED is numerically equal to the electromotive force of the power supply minus the potential barrier electromotive force of the LED divided by the total resistance of the loop (power supply internal resistance, lead resistance, LED body resistance) Sum). Therefore, the current flowing through the LED is not proportional to the voltage applied across the LED.
4. The PN junction of the LED has a negative temperature coefficient, and the potential barrier electromotive force of the LED decreases as the temperature increases. Due to this feature, the LED cannot be powered directly by a voltage source, and current limiting measures must be taken, otherwise the current will increase and even be damaged as the temperature of the LED increases.
5. The ratio of the current flowing through the LED to the luminous flux of the LED is also nonlinear. The luminous flux of the LED increases with the increase of the current flowing through the LED, but it is not proportional, and the luminous flux increases less and less later. Therefore, the LED should be operated at a current value with a relatively high luminous efficiency.

What is a Hall element?

Hall element is a device that integrates Hall element, amplifier, temperature compensation circuit and regulated power supply into one chip. Its shape is very similar to that of a transistor. The order of the three pins is: the side marked with numbers or letters. Up, from left to right are the power supply terminal, the ground terminal and the signal output terminal.

What is an electrolytic battery?

A battery in which an electrochemical reaction occurs on the electrodes under an applied voltage is called an electrolytic battery.

What should be considered in the clock generation circuit?

The first consideration is whether to use the on-chip oscillator or an external clock.