Transcript Program - kahrbjy

EE345: Introduction to Microcontrollers
The Programmable Interface
Controller (PIC): PIC 16F84
Prof. Ahmad Abu-El-Haija
Outline
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Definition of microcontroller
Architecture
Registers
Instructions
Applications
Programming Examples
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Microcontrollers versus Microprocessors
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Microcontroller differs from a microprocessor in
many ways. First and the most important is its
functionality. In order for a microprocessor to be
used, other components such as memory, or
components for receiving and sending data must be
added to it. In short that means that microprocessor
is the very heart of the computer.

On the other hand, microcontroller is designed to be
all of that in one. No other external components are
needed for its application because all necessary
peripherals are already built into it. Thus, we save
the time and space needed to construct devices
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Architecture – Typical PIC
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Architecture – PIC 16F84

PIC16F84 belongs to a class of
8-bit microcontrollers of RISC
architecture. Its general
structure is shown here
representing basic blocks.

Since PIC16F84 is a RISC
microcontroller, that means that
it has a reduced set of
instructions, more precisely 35
instructions. (ex. Intel's and
Motorola's microcontrollers
have over hundred
instructions). All of these
instructions are executed in
one cycle except for jump and
branch instructions.
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Pins of PIC 16F84
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PIC16F84 has a total of 18 pins.
It is most frequently found in a
DIP18 type of case but can also
be found in SMD case which is
smaller than a DIP. DIP is an
abbreviation for Dual In
Package. SMD is an
abbreviation for Surface Mount
Devices suggesting that holes
for pins to go through when
mounting, aren't necessary in
soldering this type of a
component.
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Pins of PIC 16F84
Pins on PIC16F84 microcontroller have the following meanings:
Pin no.1 RA2 Second pin on port A.
Pin no.2 RA3 Third pin on port A.
Pin no.3 RA4 Fourth pin on port A. TOCK1 which functions as a timer is also
found on this pin
Pin no.4 MCLR Reset input and Vpp programming voltage of a microcontroller
Pin no.5 Vss Ground of power supply.
Pin no.6 RB0 Zero pin on port B. Interrupt input is an additional function.
Pin no.7 RB1 First pin on port B.
Pin no.8 RB2 Second pin on port B.
Pin no.9 RB3 Third pin on port B.
Pin no.10 RB4 Fourth pin on port B.
Pin no.11 RB5 Fifth pin on port B.
Pin no.12 RB6 Sixth pin on port B. 'Clock' line in program mode.
Pin no.13 RB7 Seventh pin on port B. 'Data' line in program mode.
Pin no.14 Vdd Positive power supply pole.
Pin no.15 OSC2 Pin assigned for connecting with an oscillator
Pin no.16 OSC1 Pin assigned for connecting with an oscillator
Pin no.17 RA2 Second pin on port A.
Pin no.18 RA1 First pin on port A.
EE345 - Introduction to Microcontrollers
April 7, 2017
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Crystal (XT) oscillator
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Crystal oscillator is kept in metal
housing with two pins where you have
written down the frequency at which
crystal oscillates. One ceramic capacitor
of 30pF whose other end is connected
to the ground needs to be connected
with each pin. Oscillator and capacitors
can be packed in joint case with three
pins. Such element is called ceramic
resonator and is represented in charts
like the one shown. Center pins of the
element is the ground, while end pins
are connected with OSC1 and OSC2
pins on the microcontroller. When
designing a device, the rule is to place
an oscillator nearer a microcontroller, so
as to avoid any interference on lines on
which microcontroller is receiving a
clock.
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Reset (Master Clear)
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Reset is used for putting the microcontroller into a 'known' condition. That
practically means that microcontroller can behave rather inaccurately
under certain undesirable conditions. In order to continue its proper
functioning it has to be reset, meaning all registers would be placed in a
starting position. Reset is not only used when microcontroller doesn't
behave the way we want it to, but can also be used when trying out a
device as an interrupt in program execution, or to get a microcontroller
ready when loading a program.
In order to prevent from bringing a logical zero to MCLR pin accidentally
(line above it means that reset is activated by a logical zero), MCLR has
to be connected via resistor to the positive supply pole. Resistor should
be between 5 and 10K. This kind of resistor whose function is to keep a
certain line on a logical one as a preventive, is called a pull up.
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CPU
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Central processing unit (CPU) is the brain of a microcontroller. That part is
responsible for finding and fetching the right instruction which needs to be
executed, for decoding that instruction, and finally for its execution.
Arithmetic logic unit is responsible for performing operations of adding,
subtracting, moving (left or right within a register) and logic operations.
Moving data inside a register is also known as 'shifting'. PIC16F84 contains
an 8-bit arithmetic logic unit and 8-bit work registers.
Depending on which instruction is being executed, ALU can affect values of
Carry (C), Digit Carry (DC), and Zero (Z) bits in STATUS register.
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PORTB and TRISB
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PORTB has adjoined 8 pins. The appropriate register for data
direction is TRISB. Setting a bit in TRISB register defines the
corresponding port pin as input, and resetting a bit in TRISB
register defines the corresponding port pin as output.
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PORTA and TRISA
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PORTA has 5 adjoining pins. The corresponding register for
data direction is TRISA at address 85h. Like with port B,
setting a bit in TRISA register defines also the corresponding
port pin as input, and clearing a bit in TRISA register defines
the corresponding port pin as output.
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Memory Organization
PIC16F84 has two separate memory blocks, one for data and the
other for program. EEPROM memory with GPR and SFR
registers in RAM memory make up the data block, while FLASH
memory makes up the program block.
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Program memory
Program memory has been carried out in FLASH technology
which makes it possible to program a microcontroller many
times before it's installed into a device, and even after its
installment if eventual changes in program or process
parameters should occur. The size of program memory is 1024
locations with 14 bits width where locations zero and four are
reserved for reset and interrupt vector.
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Memory and Registers
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Data memory
Data memory consists of EEPROM and RAM memories. EEPROM
memory consists of 64 eight bit locations whose contents is not lost
during loosing of power supply. EEPROM is not directly addressable, but
is accessed indirectly through EEADR and EEDATA registers. As
EEPROM memory, there is a strict procedure for writing in EEPROM
which must be followed in order to avoid accidental writing.
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GPR registers
Locations of RAM memory are also called GPR registers which is an
abbreviation for General Purpose Registers. GPR registers can be
accessed regardless of which bank is selected at the moment.
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SFR registers
Registers which take up first 12 locations in banks 0 and 1 are registers
of specialized function assigned with certain blocks of the microcontroller.
These are called Special Function Registers.
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Memory Organization
Some instructions
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BSF: bit set in file register
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BCF TRISB,6
; RB6 is output
MOVLW: move literal (immediate number) to register W
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; RA2 is input
BCF: bit clear in file register
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BSF PORTA,3
BSF TRISA,2
MOVLW 0x6D
; 6D (in hex) W
ADDLW: ADD (or AND) literal to register W
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ADDLW 0x56
ADDLW D’56
ANDLW B’00011000’
; W+56(in hex) W
; W+56(decimal) W
; W AND B’00011000’  W
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Some instructions
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MOVWF f: move W to a file register f
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MOVWF PORTA
MOVWF TRISA
; W  PORTA
; W  TRISA
ADDWF f,d: add W & f, W+fd (destination)
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ADDWF PORTA,w
ADDWF PORTA,f
; porta+ww
; porta+wporta
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INCF PORTA,f
; porta+1porta
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DECF PORTB,w
; portb-1w
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Bit test, indirect mode
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BTFSS PORTA,3
GOTO label
BTFSC INTCON,5
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Other instructions
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CLRW
CLRF
MOVF
…
Next we see how typical instructions are explained in the data
sheet …
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INCFSZ
DECFSZ
Increment f, skip if=0
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List of All Instructions
Assembly language programming
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"Assembly language" and "assembler" are two different notions. The first
represents a set of rules used in writing a program for a microcontroller,
and the other is a program on the personal computer which translates
assembly language into a language of zeros and ones. A program that is
translated into "zeros" and "ones" is also called "machine language".
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Assembly language programming
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In order to function properly, we must define several
microcontroller parameters such as:
- type of oscillator,
- whether watchdog timer is turned on, and
- whether internal reset circuit is enabled.
All this is defined by the following directive:
_CONFIG _CP_OFF&_WDT_OFF&PWRTE_ON&XT_OSC
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Applications

Buttons are mechanical devices used to execute a break or make
connection between two points. They come in different sizes and with
different purposes. Buttons that are used here are also called "dipbuttons". They are soldered directly onto a printed board and are
common in electronics. They have four pins (two for each contact)
which give them mechanical stability.
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Example 1 – Single LED Circuit
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This circuit consists of a single LED lamp wired to Port B,
line 0, as shown below.
EE345 - Introduction to Microcontrollers
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Example 1 – Single LED Circuit

A program to turn on the LED on Port-B, line 0, requires a
few but essential processing operations. Code must
perform the following operations:
1. Define and select processor (in this case 16F84A).
2. Link-in the corresponding include file (p16f84A.inc).
3. Select the oscillator type (here external resonator, _XT
type).
4. Direct execution to the main label.
5. Initialize Port-B for output.
6. Set line 0 in Port-B high.
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Single LED Circuit – program
The program is as follows:
; File: LEDOn.asm
; Date: June 1, 2006
; Author: Julio Sanchez
; Processor: 16F84A
; Description:
; Turn on LED wired to Port-B, line 0
;===========================
; switches
;===========================
; Switches used in __config directive:
; _CP_ON Code protection ON/OFF
; * _CP_OFF
; * _PWRTE_ON Power-up timer ON/OFF
; _PWRTE_ON
; _WDT_ON Watchdog timer ON/OFF
; * _WDT_OFF
; _LP_OSC Low power crystal oscillator
; * _XT_OSC External parallel resonator/crystal oscillator
; |_____ * indicates setup values
processor 16f84A
include <p16f84A.inc>
__config _XT_OSC & _WDT_OFF & _PWRTE_ON & _CP_OFF
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Single LED Circuit – program cont’d
; variables in PIC RAM
; None used
; main program
org
0
; start at address 0
goto
main
; space for interrupt handler
org
0x04
; main program
main
; Initialize all lines in Port-B for output
bsf
STATUS, RP0
; Bank 1
movlw
B’00000000’
; w = 00000000 binary
movwf
TRISB
; Set up Port-B for output
; Note: this can also be accomplished via: tris PORTB
; Turn on line 0 in Port-B. All others remain off
bcf
STATUS, RP0
movlw
B’00000001’
movwf
PORTB
; Line 0 ON, all others OFF
; Endless loop intentionally hangs up program
wait goto
wait
end
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Example 2 – LED Flasher

A different program makes the LED in the above circuit flash on and
off. All that is necessary is a delay loop using a file register counter.
The logic turns on the LED and counts down to zero. Then it turns the
LED off and counts down again.
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The counter routine demonstrates the creation of a procedure in PIC
programming. In fact, a procedure is nothing more than a routine called
by a label at its entry point and terminated with a return statement. The
procedure is executed by a call statement to its initial label, as follows:
call delay ; Call to procedure
.
; Elsewhere in the program
delay:
; procedure instructions go here
return ; End of procedure
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LED Flasher – Delay Loop
delay:
movlw
movwf
jloop:
movwf
kloop:
decfsz
goto
decfsz
goto
return
.200
j
; w = 200 decimal
;j=w
k
;k=w
k,f
kloop
j,f
jloop
; k = k-1, skip next if zero
; j = j-1, skip next if zero
Code assumes that two variables were created in the processor’s GPR space, as follows:
; Declare variables at 2 memory locations
j
equ
0x0c
k equ
0x0d
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LED Flasher – Program
processor
16f84A
include
<p16f84A.inc>
__config _XT_OSC & _WDT_OFF & _PWRTE_ON & _CP_OFF
;=====================================================
; variables in PIC RAM
;=====================================================
; Declare variables at 2 memory locations
j
equ
0x0c
k
equ
0x0d
;=====================================================
;mainprogram
;=====================================================
org
0
; start at address 0
goto
main
;=============================
; space for interrupt handler
;=============================
org
0x04
;=============================
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LED Flasher – Program cont’d
; main program
;=============================
main:
; Initialize all line in Port-B for output
movlw
B’00000000’
; w = 00000000 binary
tris
PORTB
; Set up Port-B for output
;
; Program loop to turn LED on and off
LEDonoff:
; Turn on line 0 in Port-B. All others remain off
movlw
B’00000001’
; LED ON
movwf
PORTB
call
delay
; Local delay routine
; Turn off line 0 in Port-B.
movlw
B’00000000’
; LED OFF
movwf
PORTB
call
delay
goto
LEDonoff
;================================
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LED Flasher – Program cont’d
; delay subroutine
;================================
delay:
movlw
.200
; w = 200 decimal
movwf
j
;j=w
jloop:
movwf
k
;k=w
kloop:
decfsz
k,f
; k = k-1, skip next if zero
goto
kloop
decfsz
j,f
; j = j-1, skip next if zero
goto
jloop
return
End
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Example 3 – LED/Pushbutton
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A slightly more complex circuit contains a pushbutton
switch. In this case, the program monitors the state of the
pushbutton and lights the LED accordingly.
Next figure below shows one possible wiring for the
LED/pushbutton circuit.
If a switch reports a zero bit when active, it is described as
active-low. A switch that reports a one-bit when pressed is
said to be active-high. The pushbutton switch on the figure
is active-low.
In the same manner, an output device can be wired so that
it is turned on with a logic 0 and off with logic 1 on the port
pin.
EE345 - Introduction to Microcontrollers
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LED/Pushbutton Circuit
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LED/Pushbutton – Program
; Configure as before
main:
; Initialize all lines in Port-B for output
movlw
B’00000000’
; w = 00000000 binary
tris
PORTB
; Set up Port-B for output
; Initialize Port-A, line 0, for input
movlw
B’00000001’
; w = 00000001 binary
tris
PORTA
; Set up RA0 for input
; Program loop to test state of pushbutton switch
; read PB switch state
LEDctrl:
; Push button switch on demo board is wired to Port-A bit 0
; Switch logic is active low
btfss
PORTA,0
; Test. Skip next line if bit is set
goto
turnOFF
; Turn LED off routine
; At this point Port-A bit 0 is not set
; Switch is pressed (active low action)
; Turn ON line 0 in Port-B
bsf
PORTB,0
; RB0 high
goto
LEDctrl
turnOFF:
; Routine to turn OFF LED
bcf
PORTB,0
; RB0 low
goto
LEDctrl
End
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We hope material was clear & useful ….
PIC is much more complex ….
You will spend all of next course studying it.
GOOD LUCK !
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April 7, 2017
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