Classification of PIC 8-bit microcontrollers

Single chip microcomputer STM32L151CCU6

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There are three series of PIC 8-bit microcontroller products, namely basic, intermediate and advanced.

A Basic Series This product is characterized by low price, such as PIC16C5X, which is suitable for a variety of cost-sensitive home appliances. Another example is the PIC12C5XX, the world's first 8-pin low-cost single-chip microcomputer. Because of its small size, it can be used in the space of home appliances that could not be used before.

B Intermediate Series This class is the most versatile series of PIC. It has been improved on basic products and maintains high compatibility. The external structure is also available in a variety of packages from 8-pin to 68-pin, such as the PIC12C6XX. This class of products has high performance, such as internal A / D converter, E2PROM data memory, comparator output, PWM output, I2C and SPI interfaces. The PIC mid-range range is suitable for the design of a wide range of high, medium and low gear electronics.

cAdvanced Series This series of products, such as PIC17CXX, is characterized by high speed, so it is suitable for high-speed digital computing applications, and it can complete 8×8 (bit) binary multiplication in one instruction cycle (160ns). So it can replace some DSP products. In addition, PIC17CXX has rich I/O control functions, and can be extended with EPROM and RAM, making it one of the highest performance models in 8-bit MCUs. Therefore, it is very suitable for use in high and mid-range electronic equipment.

The above three-level (level) PIC 8-bit microcontrollers also have high code compatibility, making it easy for users to convert code from one model to another. The PIC 8-bit MCU has the advantages of less instructions and faster execution. The main reason is that the PIC series MCUs are different in structure from other MCUs. This series of single-chip microcomputers introduces a dual-bus and two-stage instruction pipeline structure originally used for small computers. This structure is structurally different from a microcontroller that generally uses a CISC (Complex Instruction Set Computer).

The above three-level (level) PIC 8-bit microcontrollers also have high code compatibility, making it easy for users to convert code from one model to another. The PIC 8-bit MCU has the advantages of less instructions and faster execution. The main reason is that the PIC series MCUs are different in structure from other MCUs. This series of single-chip microcomputers introduces a dual-bus and two-stage instruction pipeline structure originally used for small computers. This structure is structurally different from a microcontroller that generally uses a CISC (Complex Instruction Set Computer).

Dual bus structure

A single-chip microcomputer with a CISC structure fetches instructions and data in the same memory space, and there is only one bus in the chip. This bus has both instructions and data to be transferred (as shown in Figure 1-a). Therefore, it is not possible to access both program memory and data memory at the same time. Because there is only one kind of bus directly connected to the CPU, it is required to pass data and instructions at the same time. Obviously, it is a "bottleneck". The data and instructions in the bottle are poured out together, and the bottleneck is often stuck. Therefore, a single-chip microcomputer having such a structure can only take out an instruction first, and then execute the instruction (in the process, it is often necessary to take a number), and then, after the execution of the instruction is completed, another instruction is taken out, and the next one is continued. This structure is often referred to as the von Neumann structure, also known as the Princeton structure.

Here PIC series MCU uses a dual bus structure, the so-called Harvard structure. This structure has two types of buses, a program bus and a data bus. These two buses can use different word lengths. For example, the PIC series MCU is an eight-bit machine, so its data bus is of course eight bits. However, the low-end, mid-range, and high-end PIC series machines have 12-bit, 14-bit, and 16-bit instruction buses, respectively. In this way, when the instruction is fetched, the instruction bus is used, and when the data is fetched, the data bus does not conflict with each other.