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Introduction to the Introduction to the PIC MicrocontrollerPIC Microcontroller
OutlineOutline
What is Microcontroller? µC vs General-Purpose µP A Brief History of PIC µC PIC16F84 Features PIC Clock Generator Reset PORTS Center Processing Unit (CPU) MEMORY ORGANIZATION Timer & Prescalar Flash Memory RAM ROM EEPROM
What is What is Microcontroller?Microcontroller? Integrated chip that
contains CPU, RAM, some form of ROM, I/O ports, and timers
Designed for a very specific task to control a particular system
reduce production cost
µC µC vs General-Purpose vs General-Purpose µµPP
Microcontroller MicroprocessorDevices Microchip’s PIC’s
series, Atmel’s AVR series
Intel’s x86 family (8086, 80286, 80386, 80486 & the Pentium) or (Motorola’s PowerPC family)
Components Internal CPU, RAM, ROM, I/O ports and timers
External RAM, ROM, and I/O ports
Application Perform specific function: A small set of signal processing functions for digital signal processor
Perform more tasks that related to general requirements: calculations of software, personal computer
µC µC vs General-Purpose vs General-Purpose µµPP
Cont…
CPU / μP
Register
Control Unit
ALUDATA BUSCPU / μP
Register
Control Unit
ALU
ADDRESS BUS
CONTROL BUS
μC
RAM ROM I/O Timer Serial COM
µC µC vs General-Purpose vs General-Purpose µµPP
Cont…
Mic
ropr
oces
sor
EEPROM
RAM
Inputand
outputports
Serial I/O
Parallel I/O
Timer
PWM
Inputand
outputports
A/D
D/A
AnalogI/O
ROM
Mic
ropr
oces
sor
EEPROM
RAM
Inputand
outputports
Serial I/O
Parallel I/O
Timer
PWM
Inputand
outputports
A/DA/D
D/AD/A
AnalogI/O
ROM
Microprocessor-based System Microcontroller-based System
A Brief History of PIC A Brief History of PIC µCµC In 1989, Microchip Technology Corporation
introduced an 8-bit µC called PIC (Peripheral Interface Controller).
This 8 pins chip contains a small amounts of data RAM, a few hundred bytes of on-chip ROM for program, one timer, and a few pins for I/O ports.
The family of 8-bit µC: 10xxx, 12xxx, 14xxx, 16xxx, 17xxx, and 18xxx
A Brief History of PIC A Brief History of PIC µCµC
Cont…
http://www.microchip.com
A Brief History of PIC A Brief History of PIC µCµC They are all 8-bit processors that the CPU can
work on only 8 bits of data a time. Problem: not all 100% upwardly compatible in
terms of software when going from one family to another family.
Ex.: 12xxx - 12-bit wide instructions 16xxx- 14-bit wide instructions PIC18xxx - 16-bit wide with many
new instructions
Cont…
A Brief History of PIC A Brief History of PIC µCµCAdvantages of PIC:
30 to 100 times faster than other µCs (program memory is integrated to the chip)
Smaller size (on-board memory) Easy to program, reusable and inexpensive
Cont…
A Brief History of PIC A Brief History of PIC µCµCArchitecture:
Cont…
CPU Program & Data Memory
Von Neumann architecture
CPU Program Memory
Data Memory
Harvard architecture
PIC16F84 FeaturesPIC16F84 Features 18 pins, DIP18 type (Dual in Package) or SMD type
Remarks:RA0 - RA3: Pins on port A. No additional functionRA4 : TOCK1 which functions as a timerRB0 : Interrupt input is an additional function.RB1 - RB5: Pins on port B. No additional function.RB6 : 'Clock' line in program mode.RB7 : 'Data' line in program modeMCLR : Reset input and Vpp programming voltageVss : Ground of power supply.Vdd : Positive power supply pole.OSC1 - OSC2 : Pins for connecting with oscillator.
PIC16F84 FeaturesPIC16F84 Features Cont…
Block Block diagram of diagram of PIC16F84PIC16F84
PIC Clock GeneratorPIC Clock Generator
To provide a clock for executing a program or program instructions of C.
Types of PIC clock generator: A crystal & two capacitors Resonators or external resistor-capacitor pair Built-in resistor-capacitor
PIC Clock GeneratorPIC Clock Generator
PIC16F84 can operate in four different oscillation modes:- LP low power crystal- XT crystal/resonator- HS high speed crystal/resonator- RC resistor/capacitor
Two configuration bits, FOSC1 & FOSC0 are used to select one of these four modes
Cont…
PIC Clock GeneratorPIC Clock GeneratorCrystal Oscillator/Ceramic Resonators For XT, LP or HS OSC configurations Crystal or ceramic resonator is connected to
the OSC1/CLKIN & OSC2/CLKOUT pins
Cont…
PIC Clock GeneratorPIC Clock Generator
A parallel cut crystal is used to design PIC16F84A The use of a series cut crystal may give a freq. out of the crystal
manufacturer’s specifications
Cont…
External clock input operations
PIC Clock GeneratorPIC Clock Generator Cont…
Capacitor selection for ceramic resonators
Capacitor selection for crystal resonators
PIC Clock GeneratorPIC Clock Generator
RC Oscillator
Reduce cost for timing insensitive applications Variation of the oscillator frequency:
- operating temperature- process parameter variation- difference in lead frame capacitance between package types (low
CEXT values)- tolerance of the external R & C components
Cont…
ResetReset Power-on Reset (POR) MCLR during normal operation MCLR during SLEEP WDT Reset (during normal
operation) WDT Wake-up (during SLEEP)
Register Reset value (hex)PC 000000
WREG 00
SP 00
TRISA-TRISB FF
Value registers upon reset
PORTSPORTS
Physical connection of CPU and outside world – monitor @ control other components @ devices
A group of pins which can be accessed simultaneously @ set the desired combination of zeros and ones
All port pins can be designated as input @ output
PORTS: PORTS: PORTA & TRISAPORTA & TRISA PORTA is a 5-bit wide, bi-directional port TRISA: data direction register of PORTA TRISA = 1, PORTA
is an input (output driver in HI-impedance mode)
TRISA = 0, PORTA is an output (contents of the output latch on the selected pin)
PORTS: PORTS: PORTB & TRISBPORTB & TRISB PORTB is a 8-bit wide, bi-directional port TRISB: data direction register of PORTB TRISB = 1, PORTB
is an input (output driver in HI-impedance mode)
TRISB = 0, PORTB is an output (contents of the output latch on the selected pin)
Center Processing Unit Center Processing Unit (CPU)(CPU) The brain of the C
Connect all parts of the C through a data bus & and an address bus
Find, fetch, decode & execute the right instruction
CPU resources: Registers: store temporary information ALU: performing arithmetic functions Program counter: point to the address of
the next instruction to be executed Instruction decoder: interpret the
instruction fetched into the CPU
Center Processing Unit Center Processing Unit (CPU)(CPU)
MOVLW 0x20
Program Memory
Temporary storage
executeexecute
Memory11 00xx 0010 0000
opcode
Assembler (translator)
Decoder
Fetch instruction
Fetch instruction
Center Processing Unit Center Processing Unit (CPU)(CPU)Arithmetic Logic Unit (ALU) Add, subtract, move (left @ right within a register) and logic operations PIC16F84 contains an 8-bit ALU & 8-bit working registers (WREG) ALU instructions: two operands @ one operand Two operands: WREG + file register @ immediate constant Registers: GPR (General Purposes Registers) & SFP (Special Function Registers) One operand: WREG @ a file register Execution of ALU instructions can affect STATUS bits which are carry (C), digit carry (DC), and zero (Z).
Cont…
Center Processing Unit Center Processing Unit (CPU)(CPU)
Cont…
ALU STATUS register
8-bit literal (from instruction word)
WREG register
8-bit
8-bit
8-bitZ, DC, C flags
Carry bit
MEMORY MEMORY ORGANIZATIONORGANIZATION PIC16F84 has two separate memory blocks: data
& program Data block: GPR and SFP registers in RAM
memory (read/write memory- static memory), EEPROM memory
Program block: FLASH memory
Memory organization of PIC16F84
MEMORY ORGANIZATION:MEMORY ORGANIZATION: Program Program MemoryMemory
Used for storing programs (opcodes), directly under control of program counter (PC) Wake up memory (address 0000H) when PIC is powered up. Has been carried out in FLASH technology (indicated by the letter F in the part number, C for one-time programmable (OTP)): possible to program a C many times Size of 1024 locations, 14 bits width Locations 0000h & 0004h are reserved for reset & interrupt vector, respectively The 1st 1Kx14 (0000h-03FFh) are physically implemented address Accessing a location of physically implemented address will cause a wraparound
MEMORY ORGANIZATION:MEMORY ORGANIZATION: Program Program MemoryMemory
MEMORY ORGANIZATION:MEMORY ORGANIZATION: Data Data MemoryMemory
Also known as file register: data storage, scratch pad & registers for internal use and functions Special Function Registers (SFR)
- 8-bit wide - ALU status, timers, serial communication, I/O ports, ADC, & etc.- function of each SFR is fixed in design, used to control C or peripheral- access either directly (names @ addresses) or indirectly (FSR – File Select
Register)- classified into core and peripheral sets- control bits (RP1, RP0) in STATUS register are used for bank selection
General Purpose Registers (GPR)- 8-bit wide- also called general purpose RAM (GP RAM)- used for data storage & scratch pad- accessed directly- addresses in Bank 0 & Bank 1 are mapped together
Location of SFR and GPR vary from chip to chip, even among members of the same family
Data Memory Organization
SFR File Memory
Legend: x = unknown, u = unchanged, - = unimplemented, read as '0', q = value depends on conditionNote 1: The upper byte of the program counter is not directly accessible. PCLATH is a slave register for PC<12:8>. The contents of PCLATH can be
transferred to the upper byte of the program counter, but the contents of PC<12:8> are never transferred to PCLATH.2: The TO and PD status bits in the STATUS register are not affected by a MCLR Reset.3: Other (non power-up) RESETS include: external RESET through MCLR and the Watchdog Timer Reset.4: On any device RESET, these pins are configured as inputs.5: This is the value that will be in the port output latch.
Timer & PrescalarTimer & Prescalar
Establish relation between a real dimension such as “time” and a variable which represents status of a time within a microcontroller
PIC16F84 has an 8-bit timer, whose its value is continually increasing to 255 and then it starts all over again: 0, 1, 2, 3, …, 255, 0, 1,… etc
Prescaler divides oscillator clock before it reaches logic that increases timer status.
The first three bits in OPTION register defines divisor
256 is the highest divisor, means timer clock would increase by one at every 256th clock
Timer & PrescalarTimer & Prescalar Cont…
Flash MemoryFlash Memory
Store permanent information on some palm-sized computers (operating system & core applications)
Unlike RAM (random-access memory), flash memory can continue to store information in the absence of a power source.
Unlike ROM (read-only memory), we can write/update to flash memory
More expensive than ROM
RAMRAM
Random-access memory The most common computer memory to perform
necessary tasks while the computer is on An integrated circuit memory chip allows
information to be stored or accessed in any order and all storage locations are equally accessible.
ROMROM
Read Only Memory Non-volatile: hold programs and
data that must be retained even the computer is turned off
data cannot be easily written to ROM; depending on the technology used in the ROM, writing may require special hardware, or may be impossible.
A computer's BIOS may be stored in ROM.
EEPROMEEPROM
Electrically Erasable Programmable Read Only Memory
ROM that can be erased electronically and reprogrammed in-circuit (or with a device programmer).
EEPROM is very similar to flash memory. The biggest difference is that the bytes (words) of an EEPROM can be erased individually.
