PIC microcontroller application design and examples

1. Introduction
As the application of microcontrollers becomes increasingly widespread, applications in various fields have also put forward higher requirements for microcontroller manufacturers, hoping for faster speed, lower power consumption, smaller size, lower price and fewer peripheral devices required when composing the system; with the increasing application needs of various non-electronic engineering and technical personnel, they want to apply microcontrollers as embedded components to their familiar fields, and also put forward the requirements of being simple, easy to learn and easy to use. The needs of users are the market and motivation of manufacturers. Old semiconductor manufacturers continue to launch new varieties in line with the trend, and new semiconductor manufacturers come from behind to integrate more and more peripheral interface devices into the chip, with more and more powerful functions and higher performance. So far, at least 35 foreign semiconductor manufacturers have entered the Chinese market with their microcontrollers. Among these many colorful microcontrollers, the PIC series microcontrollers of Microchip Technology Company in the United States have emerged as a new force and are unique. It was the first to launch an 8-bit embedded controller with high performance and price ratio using a reduced instruction set computer (RISC--Reduced Instruction Set Computer), Harvard dual bus and two-stage instruction pipeline structure. Its high speed (each instruction can be as fast as 160ns), low operating voltage (the lowest operating voltage can be 3V), low power consumption (3V, 15µA at 32kHz), large input and output direct LED driving capability (sink current can reach 25mA), low price of one-time programming (OTP--One Time Programmable) chips, small size, simple and easy to learn and use instructions (35--37 instructions), etc., all reflect the new trend of the development of the microcontroller industry.
This series of microcontrollers is extremely competitive in the market. PIC microcontrollers can be seen in various fields around the world, from office automation equipment, consumer electronics, telecommunications, intelligent instruments and meters to automotive electronics, financial electronics, industrial control, etc. The PIC series of microcontrollers has been advancing year by year in the world microcontroller market share ranking, and has become a new world standard for 8-bit microcontrollers and the most influential mainstream embedded controller. You will find that Intel's MCS-51 series and its compatible microcontrollers are still the absolute mainstream in China. The reason is that this series of microcontrollers has the longest history of introduction, has been prosperous and widely used in China, has relatively rich reference materials, and is used out of inertia.

2. PIC series microcontroller system expansion technology
There are two different methods for system expansion, one is parallel expansion and the other is serial expansion.
For parallel expansion, most of the microprocessors and microcontrollers currently used use a bus structure. Whether it is memory expansion or I/O interface expansion, the three buses of data bus, address bus and control bus are used for expansion. Because the design of this series of microcontrollers is based on real microcontroller applications, the chip pins are not arranged with three buses. However, the interface circuit can be used to simulate three buses. Any microcontroller, as long as there are enough I/O interfaces available, can use an 8-bit I/O port as an 8-bit I/O port to simulate a 16-bit address line (in fact, it can also be expanded to any bit data line and address line as needed). Of course, this method occupies too many I/O port resources and is not economical. Another available method is to imitate Intel's 8031 ​​expansion method, occupying an 8-bit latch to separate the address signal; then expand the size of the device addressing range as needed, and use several bits of another I/O port as the high-order address line. The device that needs to be expanded can be connected to the corresponding signals of these three buses. When it is necessary to access the expanded device, the high-order address can be output first from the I/O port of the high 8-bit address line, and then the low-order address can be output from the time-sharing multiplexed I/O port, and another I/O line can be used as the address latch enable signal line ALE to control the latch and latch the 8-bit low-order address. At this time, the addressing unit can be accessed. The following parallel expansions all use this solution.

For serial expansion, it is relatively simple, because the PIC16CXX series chip already has a synchronous serial port component SSP, which can directly perform I²C mode and SPI mode serial communication, and there is also an asynchronous communication interface USART. There is no serial communication component in the PIC16C5X series chip, but it can be implemented by software simulation.
PIC series microcontroller system expansion technologies include: 1. Data memory expansion, (1) Parallel data memory expansion (2) Serial data memory expansion, for example, two-bus EEPROM and three-bus EEPROM with serial EEPROM, PIC16C5X and 24XXXX series serial EEPROM interface, expansion of the address space technology specified by the I²C bus protocol - 16C54 and 24LC65 interface method and programming, 16C5X and four-wire serial EEPROM chip 93LC46 interface method and programming, 16CXX SPI interface and 93LCXX interface. 2. PIC series microcontroller I/O port expansion (1) 74 series TTL integrated circuit chip expansion technology (2) Programmable parallel interface expansion technology (3) Use PIC16C5X to realize the function of digital potentiometer (4) Human-computer dialogue keyboard, LED digital display, LCD driver expansion, use PIC16C57 to directly expand LED digital tube and keyboard, use PIC16C54/56 to expand LED digital tube and keyboard, use PIC series microcontroller to directly drive LCD display. 3. Expansion and implementation of interrupt system, (1) Software interrupt technology (2) PORTB port as external interrupt. 4. I²C bus interface and serial communication, (1) I²C bus software design and its subroutines (2) Software implementation of asynchronous serial communication (3) Software implementation of PIC16CXX series asynchronous serial communication interrupt driver
3. PIC series microcontroller application system development and common tools
The development of single-chip microcomputer application system, the application system or product developed and designed by single-chip microcomputer, is different from the device implemented purely by hardware circuit. This is because in addition to the corresponding hardware circuit, the key lies in the development of application system software, and the single-chip microcomputer itself does not have software development function. How to debug and modify the written application program? How to efficiently find errors in the application system hardware and software? How to solidify the debugged program into the single-chip microcomputer on-chip program memory? These require corresponding development tools, called development systems. They mainly include single-chip microcomputer assembly language compiler, online real-time emulator ICE (Incircuit Emulator), non-online emulator (software simulation simulator Simulator), programmer, EPROM eraser, etc. Hardware debugging may also use logic analyzers, etc.
Common tools for system development include: 1. PIC assembler (1) PICASM assembler (2) MPALC assembler (3) MPASM macro assembler (4) MPASM assembly language. 2. Software simulator MPSIM. 3. Real-time online hardware simulator, (1) Real-time online simulator PICMATE (2) EasyPack-PIC 16F advanced simulator. 4. Microcontroller built-in program memory programmer, (1) PICPROG programmer (2) PRO MATE programmer

4. MPLAB integrated development environment (IDE) software
MPLAB is a Windows-based, easy-to-learn and easy-to-use integrated development environment (IDE--Intergrated Development Environment) for Microchip Technology's PIC16/17 microcontroller series. This integrated development environment allows application system development engineers to edit, assemble, simulate, develop, utilize and debug conveniently and flexibly.
MPLAB integrated development environment software integrates the following development tools. (1) Project Manager (2) MPLAB Editor (3) MPLAB Assembler (4) MPLAB-SIM Software Simulator (5) PICMASTER Hardware Online Emulator (PICMASTER Emulator), and other tools. 5.

Application Examples of PIC Series Microcontrollers
The PIC series microcontrollers have a wide range of applications, such as: 1. AC digital voltmeter 2. Electricity frequency meter 3. Flash alarm 4. Hotel mobile room controller with world clock 5. Uninterruptible power supply controlled by PIC16C71 6. Use PIC microcontroller to generate uniformly distributed random numbers 7. Use PIC17C42 to implement 4th-order IIR digital filter 8. Use PIC17C42 to implement FFT algorithm 9. Instant water heater temperature controller 10. Standard parallel interface Chinese character thermal micro printer 11. Application of I²C bus interface in PIC16CXX chip.