8位PIC16单片机C语言编程实战指南

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"8位单片机C语言编程：基于PIC16的经典教程，结合16位单片机教程，提供全面的嵌入式系统学习资源。" 本文将深入探讨8位单片机C语言编程，特别是针对PIC16系列芯片。在现代科技中，嵌入式微控制器无处不在，从手机、计算器到MP3播放器，再到各种家用电器，如洗衣机、车库门开启器等，都离不开它们的身影。这些设备通常包含多个控制器，分别负责用户界面、电机控制和整体系统管理。过去，学习如何使用微控制器面临许多障碍。程序下载器价格昂贵，开发应用需要可编程窗口部件，成本是一次性编程（OTP）版本的十倍左右，还需要紫外线擦除器来清除窗口部分的程序。调试工具更是专业人员的专属。然而，随着技术的进步，现在的大多数微控制器采用电擦除式闪存作为程序存储器，这意味着开发者可以在不需额外硬件的情况下进行程序的反复编写和调试。 PIC16系列是Microchip Technology公司生产的一系列低功耗、高性能的8位微控制器，广泛应用于各种嵌入式系统设计。使用C语言编程，开发者可以利用其简洁、结构化的语法，提高代码的可读性和可维护性，同时降低了入门难度。C语言的通用性也使得移植代码到其他类型的微控制器变得更加容易。本教程将覆盖以下核心知识点： 1. PIC16微控制器架构：了解PIC16的内部结构，包括寄存器布局、指令集和中断系统。 2. C语言基础：重温C语言的基本语法，包括变量、数据类型、运算符、流程控制语句等。 3. 针对PIC16的C语言编程：学习如何使用特定于器件的库函数，以及如何进行低级硬件操作，如端口输入/输出、定时器配置和中断服务子程序。 4. 编程环境与工具：介绍如何设置和使用集成开发环境（IDE），如MPLAB X IDE，以及编程器和仿真器的使用。 5. 调试技巧：学习如何利用内置的调试功能进行程序的调试和优化，以及如何阅读和分析调试信息。 6. 应用实例：通过实际项目，如LED控制、传感器接口和电机驱动等，加深对理论知识的理解和实践技能的掌握。 7. 电源管理：理解低功耗模式，如何在电池供电的系统中有效地管理电源。此外，配合16位单片机教程，读者可以扩展知识范围，了解更高级的微控制器特性，如更大的内存空间、更多的外设接口和更复杂的处理能力。这将有助于读者全面地理解微控制器的使用，并具备解决更复杂系统问题的能力。这本8位单片机C语言编程教程，结合16位单片机的内容，是学习嵌入式系统开发的理想资源，无论你是初学者还是有一定经验的开发者，都能从中受益匪浅，掌握实际的微控制器编程技能。

6 Part 1

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Table 1.1 : PIC16F877 Simplified File Register Map

Bank 0 (000–07F) Bank 1 (080–0FF) Bank 2 (100–180) Bank 3 (180–1FF)

Address Register Address Register Address Register Address Register

000 h

Indirect

080 h

Indirect

100 h

Indirect

180 h

Indirect

001 h

Timer0

081 h

Option

101 h

Timer0

181 h

Option

002 h

Prog.

count.

low

082 h

Prog.

count.

low

102 h

Prog.

count.

low

182 h

Prog.

count.

low

003 h

Status reg

083 h

Status reg

103 h

Status reg

183 h

Status reg

004 h

File select

084 h

File select

104 h

File select

184 h

File select

005 h

Port A

data

085 h

Port A

direction

105 h

—

185 h

—

006 h

Port B

data

086 h

Port B

direction

106 h

Port B

data

186 h

Port B

direction

007 h

Port C

data

087 h

Port C

direction

107 h

—

187 h

—

008 h

Port D

data

088 h

Port D

direction

108 h

—

188 h

—

009 h

Port E

data

089 h

Port E

direction

109 h

—

189 h

—

00A h

Prog.

count.

high

08 Ah

Prog.

count.

high

10 Ah

Prog.

count.

high

18 Ah

Prog.

count.

high

00 Bh

Interrupt

control

08 Bh

Interrupt

control

10 Bh

Interrupt

control

18 Bh

Interrupt

control

00Ch–

01Fh

peripheral

control

registers

08Ch–

09Fh

peripheral

control

registers

10Ch–

10Fh

peripheral

control

registers

18Ch–

18Fh

peripheral

control

registers

110h–

11Fh

16 general

purpose

registers

190h–

19Fh

16 general

purpose

registers

020h–

06Fh

80 general

purpose

registers

0A0h–

0EFh

80 general

purpose

registers

120h–

16Fh

80 general

purpose

registers

1A0h–

1EFh

80 general

purpose

registers

070h–

07Fh

common

access

GPRs

0F0h–

0FFh

Accesses

070h–

07Fh

170h–

17Fh

Accesses

070h–

07Fh

1F0h–

1FFh

Accesses

070h–

07Fh

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PIC Microcontroller Systems 7

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RAM File Registers

The main RAM block ( Table 1.1 ) is a set of 368 8-bit file registers, including the special

function registers (SFRs), which have a dedicated function, and the general purpose

registers (GPRs). When variables are created in C, they are stored in the GPRs, starting at

address 0020 h. The file registers are divided into four blocks, register banks 0 to 3. The

SFRs are located at the low addresses in each RAM bank.

Some registers are addressable across the bank boundaries; for example, the status

are addressable in only a specific page, for example, Port A data register. Some register

addresses are not physically implemented. Since some registers are accessible in multiple

banks, bank switching can be minimized by the compiler when assembling the machine

code, thus saving program code space and execution time. For full details of the file

The program counter uses two 8-bit registers to store a 13-bit program memory address.

Only the low byte at address 002 h is directly addressable. The status register 003 h

records results from ALU (arithmetic and logic unit) operations, such as zero and carry/

borrow. The indirect and file select registers are used for indexed addressing of the GPRs.

Timer0 is the timer/counter register available in all PIC MCUs, while Timer1 and Timer2

registers are in the peripheral block. The port registers are located in Bank 0 at addresses

05 h (Port A) to 09 h (Port E) with the data direction register for each at the corresponding

location in bank 1. We can see that a total of 80 ⫹ 1 6 ⫹ 8 0 ⫹ 9 6 ⫹ 9 6 ⫽ 368 GPRs are

available for use as data RAM. Note that the number of registers used for each C variable

depends on the variable type and can range from 1 to 32 bits (1–4 GPRs).

Other PIC Chips

In any embedded design, the features of the MCU need to be matched to the application

requirements. The manufacturer needs to make sure that, as applications become more

demanding, a more powerful device of a familiar type is available. We can see this

process at work where Microchip started out producing basic chips such as the 16C84,

then developed the product range to meet the growing market. PIC microcontrollers are

currently available in distinct groups, designated the 10, 12, 16, 18, and 24 series. Their

general characteristics are outlined in Table 1.2 .

The original 16 series CMOS devices were designated as 16CXX. When flash memory

was introduced, they became 16FXXX. Currently, a limited number of devices are

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PIC Microcontroller Systems 9

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configuration register separated from the main memory block. The main options are as

follows.

Clock Options

The ‘ 877 chip has two main clock modes, CR and XT. The CR mode needs a simple

capacitor and resistor circuit attached to CLKIN, whose time constant (C ⫻ R)

determines the clock period. R should be between 3 k and 100 k, and C greater than 20 pF.

For example, if R ⫽ 1 0 k Ω and C ⫽ 10 nF, the clock period will be around 2 ⫻ C ⫻

R ⫽ 2 0 0 μ s (calculated from the CR rise/fall time) and the frequency about 5 kHz. This

option is acceptable when the program timing is not critical.

The XT mode is the one most commonly used, since the extra component cost is small

compared with the cost of the chip itself and accurate timing is often a necessity. An

external crystal and two capacitors are fitted to CLKIN and CLKOUT pins. The crystal

frequency in this mode can be from 200 kHz to 4 MHz and is typically accurate to better

than 50 ppm (parts per million) or 0.005%. A convenient value is 4 Mz, as this is the

maximum frequency possible with a standard crystal and gives an instruction execution

time of 1.000 μ s (1 million instructions per second, or 1 Mip).

A low-speed crystal can be used to reduce power consumption, which is proportional to

clock speed in CMOS devices. The LP (low-power) mode supports the clock frequency

range 32–200 kHz. To achieve the maximum clock speed of 20 MHz, a high-speed (HS)

crystal is needed, with a corresponding increase in power consumption.

The MCU configuration fuses must be set to the required clock mode when the chip is

programmed. Many PIC chips now have an internal oscillator, which needs no external

components. It is more accurate than the RC clock but less accurate than a crystal. It

typically runs at 8 MHz and can be calibrated in the chip configuration phase to provide a

more accurate timing source.

Configuration Options

Apart from the clock options, several other hardware options must be selected.

Watchdog Timer

When enabled, the watchdog timer (WDT) automatically resets the processor after a

given period (default 18 ms). This allows, for example, an application to escape from

an endless loop caused by a program bug or run-time condition not anticipated by the

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10 Part 1

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software designer. To maintain normal operation, the WDT must be disabled or reset

within the program loop before the set time-out period has expired. It is therefore

important to set the MCU configuration bits to disable the WDT if it is not intended to

use this feature. Otherwise, the program is liable to misbehave, due to random resetting of

the MCU.

Power-up Timer

The power-up timer (PuT) provides a nominal 72 ms delay between the power supply

voltage reaching the operating value and the start of program execution. This ensures

that the supply voltage is stable before the clock starts up. It is recommended that it be

enabled as a precaution, as there is no adverse effect on normal program execution.

Oscillator Start-up Timer

After the power-up timer has expired, a further delay allows the clock to stabilize before

program execution begins. When one of the crystal clock modes is selected, the CPU

waits 1024 cycles before the CPU is enabled.

Brown-out Reset (BoR)

It is possible for a transitory supply voltage drop, or brown-out, to disrupt the MCU

program execution. When enabled, the brown-out detection circuit holds the MCU in

reset while the supply voltage is below a given threshold and releases it when the supply

has recovered. In CCS C, a low-voltage detect function triggers an interrupt that allows

the program to be restarted in an orderly way.

Code Protection (CP)

The chip can be configured during programming to prevent the machine code being read

back from the chip to protect commercially valuable or secure code. Optionally, only

selected portions of the program code may be write protected (see WRT_X% later).

In-Circuit Programming and Debugging

Most PIC chips now support in-circuit programming and debugging (ICPD), which

allows the program code to be downloaded and tested in the target hardware, under the

control of the host system. This provides a final test stage after software simulation has

been used to eliminate most of the program bugs. MPLAB allows the same interface to be

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