Today's MCU vendors have a wide range of products with different performance. According to the specific situation, what model should we choose? First of all, let's clarify two concepts: Central Instruction Set (CISC) and Reduced Instruction Set (RISC). The single-chip microcomputer data line and the instruction line adopting the CISC structure are time-division multiplexed, which is called von. Neumann structure. Its instructions are abundant and its functions are strong. However, taking instructions and taking data cannot be performed at the same time. The speed is limited and the price is high. Using RISC structure of single-chip data line and instruction line separation, the so-called Harvard structure. This makes it possible to fetch and fetch data at the same time, and because the general instruction line is wider than the data line, the instruction contains more processing information than the CISC microcontroller instruction of the same type, and the execution efficiency is higher and the speed is faster. At the same time, such single-chip microcomputer instructions are mostly single-byte, and the space utilization of program memory is greatly improved, which is conducive to ultra-compact miniaturization.
8051
A single-chip microcomputer, which is also referred to as a microcontroller, is an important branch of a microcomputer. The SCM is a large-scale integrated circuit chip developed in the mid-1970s. It is a CPU, RAM, ROM, I/O interface and interrupt system on the same silicon device. Since the 80s, SCM has developed rapidly, various new products have emerged continuously, and many new high-performance models have emerged. Now it has gradually become one of the pillar industries in factory automation and control fields.
AVR and pic are 8-bit single-chip microcomputers with different 8051 structure, because of different structure, assembly instructions are also different, and is different from the 8051 using the CISC instruction set, they are all RISC instruction set, only a few dozen instructions, large Some instructions are single-cycle instructions, so they are faster than the 8051 at the same crystal frequency. Another PIC 8-bit microcontroller is the world's largest shipment of microcontrollers in the previous years, followed by Freescale's microcontroller. ARM is actually a 32-bit microcontroller, and its internal resources (registers and peripheral functions) are much larger than those of the 8051, PIC, and AVR, and it is close to the computer's CPU chip. Commonly used in mobile phones, routers and so on. DSP is actually a kind of special one-chip computer, it has from 8 to 32. It is designed to calculate digital signals. In some formulas, it is faster than the fastest CPU in current home computers. For example, a typical 32-bit DSP can perform a 32-bit by 32-bit product plus a 32-bit number in a single instruction cycle. It is used in some applications where high real-time processing is required.
AVR
High reliability, powerful functions, high speed, low power consumption, and low-cost indicators are also necessary conditions for the microcontroller to occupy the market and survive.
The early SCM was mainly due to the low level of process and design. It has always been an important measure of SCM performance, high power consumption, and poor anti-jamming performance. Therefore, a sound solution was adopted: that is, a higher frequency division factor was used to divide the clock, making the instruction Although the CMOS single-chip microcomputer with a long cycle and a slow execution speed adopts measures such as increasing the clock frequency and reducing the frequency dividing coefficient, this state does not occur. Not completely changed (51 and 51 compatible). Although some Reduced Instruction Set Microcontrollers (RISCs) were introduced here, they still follow the practice of clock division.
The introduction of AVR MCU completely broke this old design pattern, abolished the cycle of the machine, abandoned the instruction of the complex instruction computer (CISC) to pursue complete instructions, and reduced instruction sets, using words as instruction length units with rich content of operands and opcodes. Arranged in a word (this is true for single-cycle instructions where most of the instruction sets are concentrated), the instruction fetch cycle is short, instructions can be prefetched, and pipeline operations can be realized. Therefore, instructions can be executed at high speed. Of course, this increase in speed is backed by high reliability.
The hardware structure of AVR microcontroller adopts the compromise strategy of 8-bit and 16-bit machines, namely, the use of local register stack (32 register files) and single high-speed input/output scheme (ie, input capture register, output compare match register and corresponding Control logic). The instruction execution speed (1 Mips/MHz) is improved, the bottleneck phenomenon is overcome, and the function is enhanced; at the same time, the overhead of peripheral device management is reduced, the hardware structure is relatively simplified, and the cost is reduced. Therefore, the AVR microcontroller has been optimized and balanced in terms of software/hardware overhead, speed, performance, and cost. It is a cost-effective microcontroller.
To sum up, AVR has the following features
â— Harvard architecture, with 1MIPS/MHz high-speed operation processing capability;
â— RISC (Super Function Reduced Instruction Set), with 32 general-purpose working registers, overcoming the bottleneck caused by the 8051 MCU processing with a single ACC;
â— Fast access to register sets and single-cycle instruction systems greatly optimizes the size and execution efficiency of the target code. Some models of FLASH are very large and are particularly suitable for high-level language development.
â— When the output is the same as HI/LOW of the PIC, it can output 40mA (single output). When input, it can be set as a three-state high-impedance input or a pull-up resistor input, with the ability to sink current of 10mA-20mA.
â— On-chip integrated multiple frequency RC oscillators, power-on reset, watchdog, startup delay and other functions, the peripheral circuit is more simple, the system is more stable and reliable;
Most AVR on-chip resources are rich: with E2PROM, PWM, RTC, SPI, UART, TWI, ISP, AD, Analog Comparator, WDT, etc.;
â— In addition to the ISP function, most AVRs have the IAP function to facilitate the upgrade or destruction of the application. The selection of the AVR MCU series is complete, and can be applied to various occasions. AVR microcontroller has 3 levels:
Low-end Tiny Series AVR Microcontroller: Mainly Tiny11/12/13/15/26/28, etc.; Mid-range AT90S Series AVR Microcontroller: Mainly AT90S1200/2313/8515/8535, etc.; (Closing or transitioning to Mega) High-end ATmega Series AVR MCU: Mainly ATmega8/16/32/64/128 (storage capacity is 8/16/32/64/128KB) and ATmega8515/8535 and so on.
PIC
What are the advantages of PIC? Maybe you will also have such questions, so I will talk about a few of my own opinions here.
1) The biggest feature of PIC is that it does not engage in simple functional accumulation. Instead, it focuses on the actual conditions, values ​​the performance and price ratio of the product, and develops multiple models to meet different levels of application requirements. In practical terms, different applications have different requirements for the functions and resources of the microcontroller. For example, a motorcycle igniter requires a small MCU with less I/O, less RAM and program storage space, and higher reliability. If a 40-pin and powerful MCU is used, the investment will not be too large, and it will be used. inconvenient. The PIC series has dozens of models from low to high and can meet a variety of needs. Among them, PIC12C508 one-chip computer has 8 pins only, it is the smallest one-chip computer in the world.
The model has 512 bytes of ROM, 25 bytes of RAM, an 8-bit timer, an input line, and five I/O lines. The market sells for RMB 3-6 yuan. Such a single-chip microcomputer is undoubtedly very suitable for applications like motorcycle igniters. PIC's high-end models, such as PIC16C74 (not yet the most high-end models) have 40 pins, its internal resources are ROM total 4K, 192 bytes RAM, 8 A/D, 3 8-bit timers, 2 CCP modules , Three serial ports, one parallel port, 11 interrupt sources, 33 I/O pins. Such a model can be comparable to other brands of high-end models.
2) Streamlined instructions greatly improve the efficiency of their implementation. The PIC family of 8-bit CMOS microcontrollers has a unique RISC architecture. The Harvard architecture, which separates the data bus from the instruction bus, allows the instruction to have a single-word feature and allows the number of bits of the instruction code to be more than 8 bits. This compares with traditional 8-bit microcontrollers using the CISC architecture and achieves 2:1 code compression with a 4x speed increase.
3) Zero time to market. The use of PIC's low-cost OTP chip allows the microcontroller to immediately bring the product to market after its application development is completed.
4) PIC has a superior development environment. The real-time performance of the OTP microcontroller development system is an important indicator. For example, the development system of an ordinary 51-chip microcomputer mostly uses high-end models to simulate low-end models. Its real-time performance is not ideal. PIC introduced a new model at the same time the corresponding simulation chip, all development systems supported by a dedicated simulation chip, real-time performance is very good. According to my personal experience, there have been no cases where the simulation results are different from the actual operation results.
5) The pin has anti-transient capability, can be connected to 220V AC power supply through the current limiting resistor, can be directly connected to the relay control circuit, no need for optocoupler isolation, to bring great convenience to the application.
6) Thorough confidentiality. The PIC protects the code with a confidential fuse. The user burns the code and blows the fuse. Others can no longer read it unless the fuse is restored. At present, PIC adopts deep-buried fuse technology and the possibility of recovering fuses is extremely small.
7) Self-contained watchdog timer can be used to improve the reliability of program operation.
8) Sleep and low power modes. Although PIC can not be compared with the new TI-MSP430 in this respect, it can still meet the needs in most applications.
MSP430
The rapid development of the MSP430 series of single-chip microcomputers and the continuous expansion of its application range mainly depend on the following features.
Powerful Processing Capability The MSP430 family of microcontrollers is a 16-bit microcontroller that uses a Reduced Instruction Set (RISC) architecture with rich addressing modes (seven source operand addressing, four destination operand addressing), and simple 27 core instructions and a large number of analog instructions; a large number of registers and on-chip data memory can participate in a variety of operations; there are efficient table look-up processing instructions; high processing speed, instruction cycle is 125ns at 8MHz crystal drive . These features ensure that high-efficiency source programs can be produced.
In terms of computing speed, the MSP430 series microcontrollers can achieve 125ns instruction cycle under the drive of an 8MHz crystal. The 16-bit data width, the 125-ns instruction cycle, and the versatile hardware multiplier (which enables multiplication and addition) match certain algorithms for digital signal processing (such as FFT).
MSP430 series microcontroller interrupt source more, and can be nested, flexible and convenient to use. When the system is in a power-saving standby state, wake it up with an interrupt request for only 6us.
The reason why the ultra-low-power MSP430 microcontroller has ultra-low power consumption is that it has its unique features in reducing the power supply voltage of the chip and the flexible and controllable operating clock.
First of all, the power supply voltage of MSP430 series one-chip computer adopts 1.8~3.6V voltage. Thus can make it run under 1MHz clock condition, the electric current of the chip will be about 200~400uA, the lowest power consumption of the clock cut-off mode is only 0.1uA.
Second, the unique clock system design. There are two different system clock systems in the MSP430 family: the basic clock system and the frequency-locked loop (FLL and FLL+) clock system or the DCO digital oscillator clock system. Some use a crystal oscillator (32768Hz), and some use two crystal oscillators).
Since the system clock system generates the clock required by the CPU and various functions. And these clocks can be turned on and off under the control of the instruction to achieve overall power control. Because the function modules opened when the system is running are different, ie different working modes are used, the power consumption of the chips is significantly different. There is one active mode (AM) and five low power modes (LPM0~LPM4) in the system. In the standby mode, the power consumption is 0.7uA. In the power saving mode, the power consumption is as low as 0.1uA.
The system is stable. After power-on reset, the CPU is first started by DCOCLK to ensure that the program starts from the correct position to ensure that the crystal oscillator has sufficient start-up and stabilization time. The software can then set the appropriate register control bits to determine the final system clock frequency. If the crystal oscillator fails when used as the CPU clock MCLK, the DCO will automatically start to ensure the system is working properly; if the program runs away, it can be reset by the watchdog.
ARM
In 1991, ARM was founded in Cambridge, England and mainly sold chip design technology licenses. At present, microprocessors using ARM technology intellectual property (IP) cores, which we commonly refer to as ARM microprocessors, have spread across various product markets such as industrial controls, consumer electronics, communications systems, network systems, and wireless systems. Microprocessor applications based on ARM technology account for more than 75% of the market share of 32-bit RISC microprocessors. ARM technology is gradually infiltrating all aspects of our lives.
ARM company is a company specializing in the design and development of RISC-based chip technology. As an intellectual property supplier, it does not directly engage in chip production itself. It uses its transfer of design licenses to produce distinctive chips from its partner companies. The world’s major semiconductor manufacturers are from ARM. Buying ARM microprocessor cores of its design, according to their different application fields, adding appropriate peripheral circuits to form their own ARM microprocessor chips into the market. At present, dozens of large semiconductor companies all over the world use ARM's authorization, which not only enables ARM technology to obtain more third-party tools, manufacturing, and software support, but also lowers overall system costs and makes products more accessible. The market is accepted by consumers and is more competitive.
The three major features of the ARM processor are: low power consumption, 16-bit/32-bit dual instruction set, and numerous partners.
1, small size, low power consumption, low cost, high performance;
2, support Thumb (16 bit) / ARM (32 bit) dual instruction set, can be well compatible with 8-bit / 16-bit devices;
3, the use of a large number of registers, instruction execution faster;
Most data operations are done in registers.
5, addressing method is flexible and simple, high efficiency;
6, the command length is fixed.
The power of ARM's merchandise model is that it has more than 100 partners around the world. ARM is a design company and does not produce chips itself. With the transfer license system, partners produce chips.
ARM is not a single-chip microcomputer. To be precise, ARM is a processor's IP core. After the British ARM company developed the processor structure and authorized the manufacture of other chip manufacturers, the chip manufacturers can make structural and functional adjustments according to their own needs. Therefore, there are many types of ARM processors used in practice, mainly Samsung, Philips, ATMEL, The major categories produced by INTEL are different in function and use. The ARM processor core can also be embedded in other dedicated chips for use as a central processing unit. For example, Philips' MP3 decoder chip uses the ARM7 core. ARM series processors rarely integrate on-chip hardware resources and are closer to today's processors, and are not considered to be microcontrollers.
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