What is a PIC microcontroller? What are its advantages?

I. Introduction

According to statistics, the annual capacity of single-chip microcomputers in my country has reached 100-300 million pieces, and it is growing at a rate of about 16% per year, but my country's share of the world market is less than 1%. This shows that the application of single-chip microcomputers in my country has just started and has broad prospects. Cultivating talents in single-chip microcomputer application, especially popularizing single-chip microcomputer knowledge among engineering and technical personnel, has important practical significance.

There are many single-chip microcomputer manufacturers today, and their products have different performances. Which model should we choose for specific situations? First, let's clarify two concepts: centralized instruction set (CISC) and reduced instruction set (RISC). The data line and instruction line of the single-chip microcomputer with CISC structure are time-sharing multiplexed, which is the so-called von Neumann structure. It has rich instructions and powerful functions, but instruction fetching and data fetching cannot be carried out at the same time, the speed is limited, and the price is also high. The data line and instruction line of the single-chip microcomputer with RISC structure are separated, which is the so-called Harvard structure. This allows instruction fetching and data fetching to be carried out at the same time, and because the general instruction line is wider than the data line, its instructions contain more processing information than similar CISC single-chip microcomputer instructions, and the execution efficiency is higher and the speed is also faster. At the same time, the instructions of this single-chip microcomputer are mostly single-byte, and the space utilization rate of the program memory is greatly improved, which is conducive to the realization of ultra-miniaturization. The MCUs with CISC structure include Intel8051 series, Motorola and M68HC series, Atmel's AT89 series, Taiwan Winbond (Winbond) W78 series, and the PCF80C51 series of Pilips of the Netherlands; the MCUs with RISC structure include Microchip's PIC series, Zilog's Z86 series, Atmel's AT90S series, South Korea's Samsung's KS57C series 4-bit MCUs, and Taiwan's Elan's EM-78 series. Generally speaking, RISC MCUs can be used for small household appliances with simple control relationships; CISC MCUs should be used for occasions with complex control relationships, such as communication products and industrial control systems. However, the rapid improvement of RISC MCUs has made its best MCUs equally effective in occasions with complex control relationships.

According to the different program storage methods, single-chip microcomputers can be divided into three types: EPROM, OTP (one-time programmable), and QTP (mask). At the beginning, my country used ROMless single-chip microcomputers (no ROM inside the chip, and an EPROM is required outside the chip), which played a great role in the popularization of single-chip microcomputers. However, this single-chip microcomputer that emphasizes the interface cannot be widely used, and even fell into a misunderstanding. If the application of single-chip microcomputers only emphasizes interfaces, external I/O and memory, the characteristics of single-chip microcomputers will be lost. At present, most single-chip microcomputers have program storage bodies placed inside them, which brings great convenience to applications. It is worth mentioning that the price of OTP-type single-chip microcomputers used to be 3 times that of QTP, but now it has dropped to 1.5-1.2 times. It is advisable to choose OTP type to avoid the trouble of ordering cycle and batch.

2. What are the advantages of PIC series microcontrollers?

1) The biggest feature of PIC is that it does not simply pile up functions, but starts from reality, attaches importance to the performance and price ratio of products, and develops multiple models to meet the application requirements of different levels. In reality, different applications have different requirements for microcontroller functions and resources. For example, a motorcycle ignition needs a small microcontroller with fewer I/Os, less RAM and program storage space, and higher reliability. If a 40-pin and powerful microcontroller is used, the investment will be large and it will be inconvenient to use. The PIC series has dozens of models from low to high to meet various needs. Among them, the PIC12C508 microcontroller has only 8 pins and is the smallest microcontroller in the world.

This model has 512 bytes of ROM, 25 bytes of RAM, an 8-bit timer, an input line, and 5 I/O lines. The market price is 3-6 yuan. Such a single-chip microcomputer is undoubtedly very suitable for applications such as motorcycle ignition. The high-end model of PIC, such as PIC16C74 (not the highest-end model yet), has 40 pins, and its internal resources are 4K ROM, 192 bytes of RAM, 8-way A/D, 3 8-bit timers, 2 * modules, three serial ports, 1 parallel port, 11 interrupt sources, and 33 I/O pins. Such a model can be comparable to high-end models of other brands.

2) Streamlining instructions greatly improves execution efficiency. The PIC series 8-bit CMOS microcontroller has a unique RISC structure, a Harvard bus structure with separate data bus and instruction bus, which makes the instructions have a single word length and allows the number of bits of instruction code to be more than the number of bits of data. Compared with the traditional 8-bit microcontroller with CISC structure, it can achieve 2:1 code compression and increase the speed by 4 times.

3) Zero time to market: Using PIC's low-cost OTP chip allows the microcontroller to launch the product immediately after its application program is developed.

4) PIC has a superior development environment. The real-time performance of the OTP microcontroller development system is an important indicator. For example, most of the development systems of ordinary 51 microcontrollers use high-end models to simulate low-end models, and their real-time performance is not ideal. PIC launches the corresponding simulation chip at the same time as launching a new model. All development systems are supported by dedicated simulation chips, and the real-time performance is very good. In my personal experience, there has never been a case where the simulation results are different from the actual operation results.

5) Its pins have anti-transient capability and can be connected to a 220V AC power supply through a current limiting resistor. They can be directly connected to a relay control circuit without the need for optocoupler isolation, which greatly facilitates the application.

6) Complete confidentiality. PIC uses a confidential fuse to protect the code. After the user burns the code in, the fuse is blown and no one else can read it unless the fuse is restored. Currently, PIC uses a deep-buried fuse process, and the possibility of restoring the fuse is extremely small.

7) Built-in watchdog timer can be used to improve the reliability of program operation.

8) Sleep and low power mode. Although PIC cannot compare with the new TI-MSP430 in this aspect, it can still meet the needs in most applications.