Electronics Design Lab TUTORIAL PIC Microcontrollers

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Electronics Design LabTUTORIALPIC
Microcontrollers

• Francesco Tenore
• 2/10/2006

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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

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Characteristics

• RISC CPUs
• 8-bit
• 16-bit
• Number of I/O pins 4-70
• Memory types and sizes
• Flash OTP ROM
• 0.5k 256k

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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)

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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)

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Example PIC16F877A

• 5/6 Programming pins
• 8 A/D channels
• 2 Oscillator Inputs
• 2 RS-232 inputs
• 33 I/O ports

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Programming MPLab and Assembly
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MPLab

• Download _at_ http//microchip.com
• Assembly compiler for programming PICs
• Based on specific PIC instruction set
• To upload the program
• Compile Project?Build All (CtrlF10)
• Erase the device Programmer? Erase Flash Device
• Program Programmer? Program

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Instruction Set

• 35 single word instructions
• Byte oriented file register operations
• Bit oriented file register operations
• Literal and control operations

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Example 1

• Using the PIC12F683 as a 2-state switch

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Giving memory to a pushbutton
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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

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Example 2

• Using the PICs A/D converters for Pulse Width
  Modulation

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(No Transcript)
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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

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Steps for Analog-to-Digital Conversion
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 (ADRESHADRESL), 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.

• 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.

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ADC on PIC 16F877

• Configuration
• ADCON0, ADCON1
• Result
• ADRESH, ADRESL
• (See handout)

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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_at_jhu.edu if you have any
  questions.

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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
GPlt20gt to MOVWF CMCON0 digital I/O BSF
STATUS,RP0 Bank 1 CLRF ANSEL digital I/O
MOVLW 28h Set GPlt5gt and GPlt3gt as inputs
MOVWF TRISIO and set GPlt4,20gt 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 w1
ANDWF COUNTER,0 counter AND w gt
w 0x01 MOVWF TEMP
TEMP 0x01 BTFSC TEMP,0
skip if TEMP is 0 BCF GPIO,0
otherwise, clear GPIOlt0gt BTFSS TEMP,0
BSF GPIO,0 if it's 1, then
set it. LOOP2 BTFSC GPIO,5 GOTO
LOOP GOTO LOOP2 END