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EECE.3170 Microprocessor Systems Design I

Learn how to work with PICkit, MPLAB IDE, and assembler directives for programming PIC microcontrollers. Includes sample programs and debugging techniques.

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EECE.3170 Microprocessor Systems Design I

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  1. EECE.3170Microprocessor Systems Design I Instructor: Dr. Michael Geiger Fall 2016 Lecture 28: PICkit introduction

  2. Lecture outline • Announcements/reminders • HW 7 due 11/28 • HW 8: Working with PICkits—groups of up to 4 (3 preferred) • Will be due 12/9 • No lecture Wednesday, Friday (Thanksgiving) • Review • Sample programming sequences: delay, state machine • Today’s lecture: working with PICkit • Assembler directives • MPLAB IDE • Working with existing projects • Simulator • In-circuit debugging • Sample programs in assembly and C Microprocessors I: Lecture 28

  3. Review: A Delay Subroutine ; *********************************************************************************** ; TenMs subroutine and its call inserts a delay of exactly ten milliseconds ; into the execution of code. ; It assumes a 4 MHz crystal clock. One instruction cycle = 4 * Tosc. ; TenMsH equ 13 ; Initial value of TenMs Subroutine's counter ; TenMsL equ 250 ; COUNTH and COUNTL are two variables TenMs nop ; one cycle movlw TenMsH ; Initialize COUNT movwf COUNTH movlw TenMsL movwf COUNTL Ten_1 decfsz COUNTL,F ; Inner loop goto Ten_1 decfsz COUNTH,F ; Outer loop goto Ten_1 return Microprocessors I: Lecture 28

  4. Review: Strategy to “Blink” • The LEDs are toggled in sequence - green, yellow, red, green, yellow, red… • Let’s look at the lower three bits of PORTD 001=green, 010=yellow, 100=red • The next LED to be toggled is determined by the current LED. 001->010->100->001->… Microprocessors I: Lecture 28

  5. Coding “Blink” with Table Use BlinkTable movf PORTD, W ; Copy present state of LEDs into W andlw B'00000111' ; and keep only LED bits addwf PCL,F ; Change PC with PCLATH and offset in W retlw B'00000001' ; (000 -> 001) reinitialize to green retlw B'00000011' ; (001 -> 010) green to yellow retlw B'00000110' ; (010 -> 100) yellow to red retlw B'00000010' ; (011 -> 001) reinitialize to green retlw B'00000101' ; (100 -> 001) red to green retlw B'00000100' ; (101 -> 001) reinitialize to green retlw B'00000111' ; (110 -> 001) reinitialize to green retlw B'00000110' ; (111 -> 001) reinitialize to green In calling program call BlinkTable ; get bits to change into W xorwf PORTD, F ; toggle them into PORTD Microprocessors I: Lecture 28

  6. PIC microcontroller programming • Done through MPLAB IDE • Allows for generation of projects in assembly or in C • Options to generate initialization code • In-circuit debugger to view device state while hardware is actually running Microprocessors I: Lecture 28

  7. PIC assembler directives • banksellabel • Changes BSR to bank containing label • Example: banksel TRISC • cblock/endc • Used to define a block of variables • org address • Indicates starting address for block of code that follows • Address 0 in simple programs (initial PC value) • #include file • Typically used to include processor-specific definitions, macros Microprocessors I: Lecture 28

  8. Example 1: Light single LED (.asm) Start: banksel TRISC ;select bank1 bcf TRISC,0 ;make C0 an output banksel LATC ;select bank2 clrf LATC ;initialize the ; LATCH by ; turning off ; everything bsf LATC,0 ;turn on LED C0 (DS1) goto $ ;sit here forever! end Microprocessors I: Lecture 28

  9. Example 1 notes (.asm) • TRISC: controls state of Port C pins • TRISC bits = 1  corresponding pins are inputs • TRISC bits = 0  corresponding pins are outputs • LATC: used for writing data to Port C • Equivalent to writing to PORTC register • Convention: for input, read PORTC; for output, write LATC • Infinite loop at end • $ symbol—special label for current instruction Microprocessors I: Lecture 28

  10. Example 1: Light single LED (C) void main(void) { TRISCbits.TRISC0 = 0; // Pin 0 = // output LATC = 0; //clear all pins to 0 LATCbits.LATC0 = 1; // turn ON LED while(1) continue; } Microprocessors I: Lecture 28

  11. Example 1 notes (C) • Can access entire registers by name • To access individual bits, use form: regnamebits.regname# • Example:TRISCbits.TRISC0 = 0; Microprocessors I: Lecture 28

  12. Running program • Choose target device under File  Project Properties • Either use PICkit3 or Simulator • Compilation • Clean and Build • Make and Program Device (PICkit3 only) • Separate options required for debug configuration • Click arrow on right of button to build/make for debug • Window  PIC Memory Views • Allows you to view file registers and/or SFRs Microprocessors I: Lecture 28

  13. Final notes • Next time: • Working with delay • Reminders: • HW 7 due 11/28 • HW 8: Working with PICkits—groups of up to 4 (3 preferred) • Will be due 12/9 • No lecture Wednesday, Friday (Thanksgiving) Microprocessors I: Lecture 28

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