How to Design Anti-interference for Single Chip Microcomputer

火辣西米秀

How to Design Anti-interference for Single Chip Microcomputer [Copy link]

The external clock is a high-frequency noise source. In addition to causing interference to the application system, it may also cause interference to the outside world, making the electromagnetic compatibility test fail to meet the standard. In application systems that require high system reliability, the use of low-frequency microcontrollers is one of the principles for reducing system noise. Taking the 8051 microcontroller as an example, when the shortest instruction cycle is 1μs, the external clock is 12MHz. The system clock of the Motorola microcontroller of the same speed only needs 4MHz, which is more suitable for industrial control systems.

Low noise series microcontroller

In traditional integrated circuit design, the power supply and ground are usually arranged on two symmetrical sides. For example, the lower left corner is the ground, and the lower right corner is the power supply. This allows the power supply noise to pass through the entire silicon chip. The improved technology arranges the power supply and ground on two adjacent pins, which reduces the current passing through the entire silicon chip on the one hand, and makes it easier to arrange external decoupling capacitors on the PCB design to reduce system noise. Another example of reducing noise in integrated circuit design is the design of the drive circuit. Some microcontrollers provide several high-current output pins, ranging from tens of milliamperes to hundreds of milliamperes. These high-power drive circuits integrated into the microcontroller will undoubtedly increase the noise source. The softening technology of the jump edge can eliminate this effect. The method is to make a high-power tube into several small tubes in parallel, and then connect a resistor with different equivalent resistance values to the output end of each tube. To reduce di/dt.

Clock monitoring circuit, watchdog technology and low voltage reset

Monitoring the system clock and generating a system reset signal to restore the system clock when the system clock stops is one of the measures to improve the reliability of the microcontroller. However, the clock monitoring is effective and the power saving instruction STOP is a contradiction. Only one of them can be used.

Watchdog technology monitors the running status of a timer interrupt service program in the application program. When this program does not work, it is judged as a system failure, thereby generating a system reset.

The low voltage reset technology monitors the power supply voltage of the microcontroller and generates a reset signal when the voltage is lower than a certain value. With the development of microcontroller technology, the microcontroller itself has wider and wider requirements for the power supply voltage range. The power supply voltage has dropped from 5V to 3.3V and continued to drop to 2.7V, 2.2V, and 1.8V. Whether to use the low voltage reset function should be weighed according to the specific application situation.

Software measures

The microcontroller itself also has some anti-interference considerations in the instruction design. Illegal instruction reset or illegal instruction interrupt is when an illegal instruction or illegal addressing space is encountered during program execution, which can generate a reset or interrupt. The microcontroller application system program is written in advance, and there is no possibility of illegal instructions or addressing. It must be that the system is disturbed and the CPU makes an error when reading the instruction.

The above mentioned are the internal anti-interference measures that the currently widely used single-chip microcomputers should have. When selecting a single-chip microcomputer, it is necessary to check whether these performances are available in order to design a highly reliable system.

In terms of application software design, designers have their own experience. What we need to remind you here is to deal with the unused ROM at the end. The principle is that if the program falls here, it can be self-recovered.