Chapter 2 - Microcontroller Architecture & Assembly Language

8/10/2019 Chapter 2 - Microcontroller Architecture & Assembly Language

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Chapter

MICROCONTROLLER

ARCHITECTURE & ASSEMBLY

LANGUAGE

PROGRAMMING


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PIC 12F508

PIC 16F84A

PIC 16C72

Motorola 68HC05B16

PIC 16F877

Motorola 68000

Microcontroller Packaging and Appearance


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PIC microcontrollers in DIP and QFN packages

16-bit 28-pin PDIP PIC24 microcontroller next to a

metric ruler


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PIC18 Architecture

Von Neumann Architecture: Fetches instructions and data from a single memory

space

Limits operating bandwidth

Von Neumann

Architecture

8-bit Bus

CPU

Program

& Data

Memory


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Harvard Architecture:

Uses two separate memory spaces for program instructions and

data

Improved operating bandwidth

Allows for different bus widths

CPU

Harvard

Architecture

Data

Memory

Program

Memory

8-bit Bus

16-bit Bus

PIC18 Architecture


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PIC18 Microcontroller Families

PIC microcontrollers are designed using

the Harvard Architecture which includes:

Microprocessor unit (MPU)

Program memory for instructions

Data memory for data

I/O ports

Support devices such as timers


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Microcontroller with the

Harvard Architecture


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A Brief History of PIC C


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8-bit Architecture Overview


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Compare 8-bit PICMCU Architectures


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PIC18 Architecture Block Diagram


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PIC18F4450 Block Diagram


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PIC18F MCU and Memory

2 MB

221

4 KB

212

8 bit

16 bit


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Includes Arithmetic Logic Unit (ALU), Registers,

and Control Unit Arithmetic Logic Unit (ALU)

WREG working register

Status register that stores flags

Instruction decoder when the instruction is fetched it goes into

the ID


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Registers

Bank Select Register (BSR)

4-bit register used in direct addressing the data memory

File Select Registers (FSRs) 16-bit registers used as memory pointers in indirect addressing

data memory

Program Counter (PC)

21-bit register that holds the program memory address while

executing programs


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Control unit

Provides timing and control signals to various

Read and Write operations


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Address bus

21-bit address bus for

program memoryaddressing capacity: 2 MB

of memory

12-bit address bus for data

memory addressing

capacity: 4 KB of memory

Data bus

16-bit instruction/data bus

for program memory

8-bit data bus for data

memory

Control signals

Read and Write


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Data RAM File Register

In the CPU, registers are used to store information temporarily.

It could be a byte of data to be processed, or an address

pointing to the data to be fetched.

Majority of PIC registers are 8-bit registers.

In the PIC there is only one data type: 8-bit.

The range goes from the MSB (most-significant bit) D7 to the

LSB least-significant bit) D0.

With an 8-bit data type, any data larger than 8 bits must be

broken into 8-bit chunks before it is processed.


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WREG register The 8-bit WREG register is the most widely used

register in the PIC micro controller.

WREG stands for working register, as there is only one.

The WREG register is the same as the accumulator inother microprocessors.

The WREG register is used for all arithmetic and logic

instructions.


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To understand the use of the WREG register, we will

show it in the context of two simple instructions: MOVE

and ADD.

MOVLW

The MOVLW instruction MOVES 8-bit data into theWREG register. It has the following format:

MOVLW K ;move literal value Kinto WREG

MOVLW 25H ; move value 25Hinto WREG (WREG = 25H)

Is the following code correct?

MOVLW 9H

MOVLW A23H


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ADDLW

The ADDLW instruction ADD 8-bit data into the WREGregister. It has the following format:

ADDLW K ;ADD literal value K to WREG

ADDLW 34H ;ADD literal value 34H to WREG

Example:

MOVLW 12H ;move literal value 12Hinto WREG

ADDLW 16H ; add value 16Hinto WREG (WREG = 28H)

ADDLW 32H ; add value 32Hinto WREG (WREG = 60H)


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PIC WREG and ALU Using Literal Value


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It is the data memory.

Read/Write - Static RAM

Used for data storage, scratch pad and registers for internal use and function

8-bit width

File register (SFRs and GPR)


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Register relationship in PIC

PIC File Register

Special Function RegisterGeneral Purpose RAM

EEPROMGP RAM


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Register File

concept

All data memory

is part of register

file

Any location indata memory can

be operated

directly

All peripherals

mapped into datamemory as a

series of registers


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SFR Special Function Register 8 bit registers

Dedicated to specific functions such as ALU status, timers,serial communication, I/O ports, ADC etc.

Each SFR functions is fixed by the CPU designer at the time of

design and it is used for controlling microcontroller/peripheral

GPR General Purpose Register 8 bit registers

A group of RAM locations in the file register that are used for

data storage.

Larger than SFR

The microchip website provides the data RAM size, which is the same as

GPR size


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File Register Size

File Register=

SFR+

GPR

(Bytes) (Bytes) (Bytes)

PIC12F508 32 7 25

PIC16F84 80 12 68

PIC18F1220 512 256 256

PIC18F452 1792 256 1536

PIC18F2220 768 256 512

PIC18F458 1792 256 1536

PIC18F8722 4096 158 3938

PIC18F4550 2048 160 1888


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File Registers of PIC12, PIC16, and PIC18


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PIC Status Register

To indicate arithmetic conditions It is a 8-bit register

Five bits are used

D0: C Carry Flag

D1: DC Digital Carry Flag

D2: Z Zero Flag

D3: OV Overflow Flag

D4: N Negative Flag


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Bits of Status Register


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Example 1

Show the status of the C, DC, Z flags after thefollowing addition instruction

MOVLW 38H

ADDLW 2FH

Solution

38H + 2FH = 67HWREG=67H

C=0

DC=1Z=0


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Example 2

Show the status of the C, DC, Z flags after thefollowing addition instruction

MOVLW 9CH

ADDLW 64H

Solution

9CH + 64H = 100H WREG= 00H

C=1

DC=1Z=1


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Instruction That Affect

Flag Bits


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Flag Bits and Decision Making


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PIC Data Format and Directives

There is one data type

8 bits

It is the job of the programmer to break down

data larger 8 bits ( 00 to FFH or 0 to 255)

Data type can be positive or negative number

Data format are

Hex (default in PIC)12 or 0x12 or H'12' or 12H or

Binary B'00010010 or

Decimal.12 or D'12 or

ASCIIA'c' or a'c'


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Assembler Directives

What is the difference

betweenInstruction and Directives?


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Instruction Tells the CPU what to do

Directives (pseudo-instruction) Give directions to the assembler


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Assembly language Format

LABEL INSTRUCTION/ OPERAND COMMENT

ASS. DIRECTIVE

START MOVLW 12H ;move literal value 12Hinto

WREG

Label:

use to represent the location of an instruction or a value no

spacing not more than 8 characters including number.

Instruction:

tells the controller what to do. Ex. MOVWF, GOTO..

Assembler directive: tells the assembler suppose to do. Ex. EQU, ORG, END

Operand:

data to operate on / source of data to operate on and its

destination after processing.


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PIC Language Fundamental

Please refer to notes


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Arithmetic and Logic Instruction

Please refer to notes

Chapter 5: Arithmetic, Logic Instructions and

Programs

Muhammad Ali Mazidi, Rolin D. Mckinlay & Danny Causey (2008).

PIC Microcontroller and Embedded Systems:

Using Assembly and C for PIC18.

Pearson Prentice Hall. (ISBN: 9780136009023)

Chapter 2 - Microcontroller Architecture & Assembly Language

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