Electronics Design Lab
TUTORIAL
PIC Microcontrollers
Francesco Tenore
2/10/2006
The Microchip ® PIC ucontrollers
• http://www.microchip.com
• Characteristics
– types; speeds; I/O pins; Analog to Digital
Converters; Capture/Compare modules
• Programming (MPLab)
• Instruction set
• Implementations and Examples
Characteristics
• RISC CPUs
– 8-bit
– 16-bit
• Number of I/O pins: 4-70
• Memory types and sizes:
– Flash; OTP; ROM
– 0.5k – 256k
Speeds
• All PICs require oscillators to execute
instructions:
– Internal* (low speeds, up to 8 MHz)
– External (high speeds, up to 40 MHz)
• Instructions are executed at least at ¼
oscillator speed (4 clocks/instruction)
(*Note: not all PICs have internal oscillators)
A/D converters and C/C modules
• All PICs have between 0 and 16 A/D
converters with 8/10-bit resolution
• 8-16 bit Timers/Counters
• Comparator Modules (0-2)
Example: PIC16F877A
5/6 Programming pins
8 A/D channels
2 Oscillator Inputs
2 RS-232 inputs
33 I/O ports
Programming – MPLab and
Assembly
MPLab
•
•
•
•
Download @ http://microchip.com
Assembly compiler for programming
PICs
Based on specific PIC instruction set
To upload the program:
1. Compile: ProjectBuild All (Ctrl+F10)
2. Erase the device: Programmer Erase
Flash Device
3. Program: Programmer Program
Instruction Set
• 35 single word instructions
– Byte oriented file register operations
– Bit oriented file register operations
– Literal and control operations
Example 1
Using the PIC12F683 as a 2-state
switch
Giving memory to a pushbutton
Giving memory to a pushbutton
• In this example we:
– Store the state of the LED and
• Turn off if on and
• Turn on if off
Example 2
Using the PICs A/D converters for
Pulse Width Modulation
Pulse Width Modulation (PWM)
• 1-2 ms pulse used to control servomotors
• In this example, we:
– ACQUIRE an analog 0-5V signal
– CONVERT it into a 1-2 ms pulse that depends
on the analog voltage and output the result on
an output pin
– REPEAT
Steps for Analog-to-Digital
Conversion
1. Configure the A/D module:
• Configure analog pins/voltage
reference and digital I/O
(ADCON1)
• Select A/D input channel (ADCON0)
• Select A/D conversion clock
(ADCON0)
• Turn on A/D module (ADCON0)
2. Configure A/D interrupt (if desired):
• Clear ADIF bit
• Set ADIE bit
• Set PEIE bit
• Set GIE bit
3. Wait the required acquisition time.
4. Start conversion:
• Set GO/DONE bit (ADCON0)
5. Wait for A/D conversion to complete, by
either:
• Polling for the GO/DONE bit to be cleared
(with interrupts enabled); OR
• Waiting for the A/D interrupt
6. Read A/D result register pair
(ADRESH:ADRESL), clear bit ADIF if
required.
7. For the next conversion, go to step 1 or
step 2, as required. The A/D conversion
time per bit is defined as TAD. A minimum
wait of 2TAD is required before the next
acquisition starts.
ADC on PIC 16F877
• Configuration:
– ADCON0, ADCON1
• Result
– ADRESH, ADRESL
(See handout)
Samples
• The microchip website:
www.microchip.com
offers samples of PICs (maximum 5)
that are sent to you for free.
Please e-mail me at fra@jhu.edu if you have
any questions.
; EDL_test1.asm: blinks an LED when pushbutton is pressed.
#INCLUDE
"P12F683.INC"
ORG
0x000000
bsf STATUS,RP0 ;Bank 1
movlw b'01110010' ; 0x00
movwf OSCCON
; 0x01
goto START
; 0x02
ORG
0x000020
START:
COUNTER EQU 0x21
TEMP EQU 0x22
BCF STATUS,RP0 ;Bank 0
CLRF GPIO ;Init GPIO
MOVLW 07h ;Set GP<2:0> to
MOVWF CMCON0 ;digital I/O
BSF STATUS,RP0 ;Bank 1
CLRF ANSEL ;digital I/O
MOVLW 28h ;Set GP<5> and GP<3> as inputs
MOVWF TRISIO ;and set GP<4,2:0> as outputs
BCF STATUS,RP0 ;Bank 0
BSF GPIO,0
LOOP:
BTFSS GPIO,5
; skip if button NOT pressed
GOTO CLEAR_ROUTINE ; otherwise
GOTO LOOP
CLEAR_ROUTINE:
INCF COUNTER,1
; increment the counter
MOVLW 0x01
; w=1
ANDWF COUNTER,0
; counter AND w =>
; w = 0x01
MOVWF TEMP
; TEMP = 0x01
BTFSC TEMP,0
; skip if TEMP is 0
BCF GPIO,0
; otherwise, clear GPIO<0>
BTFSS TEMP,0
BSF GPIO,0
; if it's 1, then set it.
LOOP2:
BTFSC GPIO,5
GOTO LOOP
GOTO LOOP2
END