1, the smallest single-chip system? The main internal structure?
Power supply, oscillator, reset
2, single-chip IO port What is the role? Drive capability? Pull-down resistor on the role of?
It is used to define the state and the input-output mode corresponding I / O port bit
1) improve the driving ability:
For example, the microcontroller output high, but because of the follow-up circuit, the high level output is not high, is not up to the VCC, affect circuit operation. So to pull-up resistor. Instead pull-down resistor, the pin so that the microcontroller outputs a low level, a low level since the result of subsequent circuits not affect the output of the GND, so the down resistor connected.
2) When the microcontroller pin level of uncertainty, so that the back of a stable level:
For example in the case of above-ground pull-down resistor, the microcontroller just power up when the level is uncertain, there is that if you connect the microcontroller after power-up, the microcontroller pin is an input, not an output pin, that SCM level this time is uncertain, the role of R18 is that if the previous level microcontroller pins uncertain words, to force level is kept at a low level.
3, the following definitions of the variables is the wrong way
int ab_2
int _2a3
int 2_ab
int ab_2
Variable names can not start with a number
4, write the following code outputting content
#include <.h> int main(int argc, char const *argv[]) { int a,b,c,d; a = 10; b = a ++; c = ++ a; d = 10 * a ++; printf("b:%d,c:%d,d:%d\n",b,c,d); return 0; }
b:10,c:12,d:120
5, the watchdog of principle? With the watchdog under what circumstances?
Watchdog principle: the phenomenon of SCM system will appear in Runaway outside interference results in an infinite loop, the watchdog circuit is to prevent this from happening. Watchdog role is within a certain time (implemented by the timer counter) DOG signal is not received (represented MCU has been linked), they automatically reset the processor restart (reset signal transmission)
General engineering will use two watchdog, an independent watchdog, mainly for use after a reset code runaway, a window watchdog is mainly used to save before resetting some important data.
6, the MOS control motor reversing circuit, the circuit diagram shown
7, you know what common logic level? TTL and COMS level can be connected to each other thing?
Used by the other logic level TTL, CMOS, LVTTL, ECL, PECL, GTL, RS232, RS422, RS585, LVDS. Wherein the TTL and CMOS logic levels according to a typical voltage into four categories: 5V series (5V TTL and 5V CMOS), 3.3V series, 2.5V and 1.8V series series.
8, with a rope irregular combustion timing, over a complete combustion in the atmosphere of 60 minutes with.
Now we need to burn out this rope for 15 minutes. Without the aid of external tools, please explain how to solve?
a rope 2 while burning, b rope burn single head
After 30 minutes, a rope burn
At this time, the other end of the rope b ignition, timing this time, when the burn-out cord 15 minutes b
9, give you four trees need to grow four trees per tree equal distance, how to solve?
Think of ways to construct a regular tetrahedron.
1) improve the driving ability:
For example, the microcontroller output high, but because of the follow-up circuit, the high level output is not high, is not up to the VCC, affect circuit operation. So to pull-up resistor. Instead pull-down resistor, the pin so that the microcontroller outputs a low level, a low level since the result of subsequent circuits not affect the output of the GND, so the down resistor connected.
2) When the microcontroller pin level of uncertainty, so that the back of a stable level:
For example in the case of above-ground pull-down resistor, the microcontroller just power up when the level is uncertain, there is that if you connect the microcontroller after power-up, the microcontroller pin is an input, not an output pin, that SCM level this time is uncertain, the role of R18 is that if the previous level microcontroller pins uncertain words, to force level is kept at a low level.