Electronics Design Lab TUTORIAL PIC Microcontrollers Francesco Tenore 2/10/2006

The Microchip ® PIC ucontrollers 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 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

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: offers samples of PICs (maximum 5) that are sent to you for free. Please me at if you have any

; EDL_test1.asm: blinks an LED when pushbutton is pressed. #INCLUDE "P12F683.INC" ORG 0x bsf STATUS,RP0 ;Bank 1 movlw b' ' ; 0x00 movwf OSCCON ; 0x01 goto START ; 0x02 ORG 0x START: COUNTER EQU 0x21 TEMP EQU 0x22 BCF STATUS,RP0 ;Bank 0 CLRF GPIO ;Init GPIO MOVLW 07h ;Set GP to MOVWF CMCON0 ;digital I/O BSF STATUS,RP0 ;Bank 1 CLRF ANSEL ;digital I/O MOVLW 28h ;Set GP and GP as inputs MOVWF TRISIO ;and set GP 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 BTFSS TEMP,0 BSF GPIO,0 ; if it's 1, then set it. LOOP2: BTFSC GPIO,5 GOTO LOOP GOTO LOOP2 END