1 / 28

Programming the PIC16F877 in PIC MPASM Assembly Language

Programming the PIC16F877 in PIC MPASM Assembly Language. PIC16xxx Family Instruction Set. Each instruction is a single 14-bit word THREE basic categories: Byte Oriented Bit Oriented Literal (Immediate Constant) and Control

vickyf
Télécharger la présentation

Programming the PIC16F877 in PIC MPASM Assembly Language

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Programming the PIC16F877 in PIC MPASM Assembly Language ECE331 PIC Assembly (KEH)

  2. PIC16xxx Family Instruction Set • Each instruction is a single 14-bit word • THREE basic categories: • Byte Oriented • Bit Oriented • Literal (Immediate Constant) and Control • One instruction cycle consists of FOUR clock oscillator periods. Hence for a 20 MHz clock, an instruction takes 4/20MHz = 200 ns to execute. • Any transfer of control (call, jump, conditional test, or goto) instruction takes two 200 ns cycles to allow the instruction queue to be refilled. ECE331 PIC Assembly (KEH)

  3. PIC 16xxx Family Instruction Format ECE331 PIC Assembly (KEH)

  4. PIC16XXX Byte-Oriented Instructions ECE331 PIC Assembly (KEH)

  5. PIC16xxx Bit-oriented and Literal and Control Instructions ECE331 PIC Assembly (KEH)

  6. Setting the directional bit “d” • If you add the include file to your assembly program: #include "p16f877A.inc“Then the directional bit “d” value is pre-defined as “w equ 0” and “f equ 1”. So we may writemydat equ 0x20 addwf mydat,f ;mydat  mydat + W addwf mydat,w ;W  mydat + W ECE331 PIC Assembly (KEH)

  7. Some examples • MOVLW 0x12 ;Move $12 into accumulator “W” ;”Literal” => Immediate constant • MOVWF mydat ;Move W into reg file “mydat” • MOVF mydat,w ;Move reg file “mydat” into W • MOVF mydat,f ;What good is this instruction? ;(It sets the Z flag, allowing us to ;see if reg file “mydat” contains 0) • BSF mydat,3 ;Set Bit #3 of mydat | ;(Bit #0 is the LSB on right) ECE331 PIC Assembly (KEH)

  8. Branch to location “TARGET” if W =< mydat (in an unsigned sense) SUBWF mydat,f ;mydat – W BTFSC 3,0 ;Test Bit #0 of STATUS reg (the C flag) and ;skip next instruction if C is clear ;implying that a borrow was requested, ;thus implying that mydat is less than W in ;an unsigned sense. ;Remember on PIC the borrow flag is the ;inverse of the C flag (unlike the HC12).GOTO Target....EXECUTE THESE INSTRUCTIONS IF W>mydat... Target NOP ;Branch here if W =< mydat ECE331 PIC Assembly (KEH)

  9. Status Register ECE331 PIC Assembly (KEH)

  10. Example #1 LED Flasher using Software Delay Loops ;***** PIC16F877A MPASM Example #1 ***** ;NOTE: When setting up the project, be sure to choose the active ;toolsuite to be "Microchip MPASM Toolsuite" instead of the ;"Hi-Tech PICC Toolsuite" as you did with C programs. ; ;This is a simple I/O Example. When input RA0 goes HIGH, ;LED connected to output RA1 will FLASH ON/OFF at 1 s rate ;1 second delay obtained using two nested software timing loops ;************************** list p=16F877A #include "p16f877A.inc" ;include register definitions file ;also W is defined to equal 0 and ;F is defined to equal 1, so the ;destination bit(D)can be set using ;the W and F symbols. (W => result in ;working register w, while F => result ;in indicated register file location. radix dec ;make default numbers decimal values org 0 ;Reset vector is at prog loc 0x00. goto start ;Skip over INT vector at prog loc 0x04. CBLOCK 0x20 ;Use CBLOCK and ENDC to reserve a block of register file locations ;starting at address 0x20 in register file space count1 ;count1 = 0x20 count2 ;count2 = 0x21 count3 ;count3 = 0x22 count4 ;count4 = 0x23 ENDC ECE331 PIC Assembly (KEH)

  11. org 0x05 ;Start assembling program at location 5 in program space. start clrf PORTA ;Initialize port A by zeroing ;output data latches. banksel ADCON1 ;This directive switches to data bank that ;ADCON1 is found in (Bank 1). It results in ;the assembly of the following instruction: ;"bsf STATUS,5" (Set RP0 = 1) movlw 0x06 movwf ADCON1 ;Configure PORTA for digital I/O (out of reset, PORTA is analog) movlw 0x01 ;Set RA0 for input, RA1 for output movwf TRISA banksel PORTA ;This directive switches to data bank ;that is found in (Bank 0) in following ;instruction: "bcf STATUS,5" Set RP0 = 0. waitsw btfsc PORTA,0 ;check RA0 goto waitsw ;wait until switch on RA0 pressed down (RA0 goes low). movlw 5 ;Flash LED 5 times. movwf count4 flshagn bsf PORTA,1 ;turn ON LED on RA1 (LED cathode tied to ground) call wait_swloop bcf PORTA,1 ;turn OFF LED on RA1 call wait_swloop decfsz count4,f goto flshagn done goto waitsw ; ECE331 PIC Assembly (KEH)

  12. ;Subroutine wait_swloop -- delays about 1 second using nested ; software delay loops. wait_swloop movlw 80 ;all three loops count to 80 movwf count1 ;thus doubling this number loopout movwf count2 ;increases delay time by 2^3 = 8! loopmid movwf count3 loopinr decfsz count3,f goto loopinr decfsz count2,f goto loopmid decfsz count1,f goto loopout return end ECE331 PIC Assembly (KEH)

  13. Example 2. LED Flasher using Timer 0 ;***** PIC16F877 MPASM Example #2 ***** ;Simple I/O Example. When input RA0 goes HIGH, ;LED connected to output RA1 will FLASH ON/OFF at 1 s rate ;1 second delay obtained using TMR0 to wait out 100 ten-ms intervals ;************************** list p=16F877 #include "p16f877.inc" ;include register definitions file ;also W is defined to equal 0 and ;F is defined to equal 1, so the ;destination bit(D)can be set using ;the W and F symbols. (W => result in ;working register w, while F => result ;in indicated register file location. radix dec ;make default numbers decimal values org 0 ;Reset vector is at prog loc 0x00. goto start1 ;Skip over INT vector at prog loc 0x04. CBLOCK 0x20 ;Reserve reg file locns, starting at adr 0x20 in reg file space count3 ;count3 = 0x20 count4 ;count4 = 0x21 ENDC ECE331 PIC Assembly (KEH)

  14. org 0x05 ;Start assembling program at location 5 in program space. start1 banksel OPTION_REG movlw b'00000111' movwf OPTION_REG ;timer tick period = (4/10E6)*256 = 75.85 microseconds banksel PORTB ;note that 10 ms / 75.85 = 131.8, so 132 timer ticks lasts about 10 ms clrf PORTB ;Initialize port A by zeroing ;output data latches. banksel TRISB ;This directive switches to data bank that ;TRISB is found in (Bank 1). It results in ;the assembly of the following instruction: ;"bsf STATUS,5" (Set RP0 = 1) movlw 0x01 ;Set RA0 for input, RA1 for output movwf TRISB banksel PORTB ;This directive switches to data bank ;that PORTB is found in (Bank 0) in following ;instruction: "bcf STATUS,5" Set RP0 = 0. waitsw btfsc PORTB,0 ;check RA0 goto waitsw ;wait until switch on RA0 pressed down (RA0 goes low). movlw 5 ;Flash LED 5 times. movwf count4 flshagn bsf PORTB,1 ;turn ON LED on RA1 (LED cathode tied to ground) call wait_1s_tmr0 bcf PORTB,1 ;turn OFF LED on RA1 call wait_1s_tmr0 decfsz count4,f goto flshagn done goto waitsw ; ECE331 PIC Assembly (KEH)

  15. ;Subroutine wait_swloop -- delays about 1 second using nested sw delay loops ; wait_1s_tmr0 movlw 100 movwf count3 ;repeat 10 ms loop 100 times to wait 1 second wait_loop movlw 256 - 132; movwf TMR0 ;schedule TMR0 to wrap (overflow) in 10 ms. bcf INTCON,2 ;clear TMR0IF flag (bit #2 of INTCON reg) wt10ms btfss INTCON,2 ;Wait till TMR0 overflows. goto wt10ms decfsz count3,f goto wait_loop return end ECE331 PIC Assembly (KEH)

  16. Example 3. 220 Hz Square Wave using TMR0 Interrupts ;***** PIC16F877 MPASM Example #3 ***** ;Interrupt Example. 220 Hz square wave generated on RB1 ;************************** list p=16F877 ;change to 16F877A if necessary #include "p16f877.inc" radix dec ;make default numbers decimal values org 0 ;Reset vector is at prog loc 0x00. goto startpgm ;Skip over INT vector at prog loc 0x04. org 4 ;Interrupt Vector goto int_service CBLOCK 0x20 ;Reserve reg file locns, starting at adr 0x20 w_temp ;w_temp = 0x20 status_temp ;status_temp = 0x21 ENDC org 0x05 ;Start assembling program at location 5 in program space. startpgm banksel OPTION_REG movlw b'00000111‘ ;Prescale TMR0 by 256. Assuming a 13.5 MHz crystal osc freq, ;timer tick = (4/13.5 Mhz)*256 = 75.85 microseconds movwf OPTION_REG ECE331 PIC Assembly (KEH)

  17. banksel PORTB clrf PORTB ;Initialize port B by zeroing ;output data latches. banksel TRISB movlw 0xFD ;Set RB1 for output movwf TRISB banksel TMR0 movlw 256 – 30 ;(1/440.)/75.85 microseconds = 30.0 movwf TMR0 ;Schedule Timer0 to interrupt in 1/440th of a second. bcf INTCON,2 ;clear TMR0IF flag movlw b'10100000' movwf INTCON ;enable TMR0 interrupts idle_loop goto idle_loop ; ; ***** END OF MAIN PROGRAM ****** ECE331 PIC Assembly (KEH)

  18. ; ************* Start of INTERRUPT SERVICE ROUTINE ******* int_service movwf w_temp ;save w and status regs in temp locns swapf STATUS,w movwf status_temp banksel TMR0 bcf INTCON,2 ;clear TMR0IF flag (shut the baby up) movlw 256 - 30 movwf TMR0 ;schedule next TMR0 interrupt movf PORTB,W ;get PORTB into W xorlw 0x02 ;invert Bit #1 of W movwf PORTB ;Send inverted result out to RB1 swapf status_temp,w ;restore w and status flags fm temp locns movwf STATUS swapf w_temp,f swapf w_temp,w retfie end ECE331 PIC Assembly (KEH)

  19. Ex 4. Light Show: Indirect Addressing ;***** PIC Example #4 ***** ;Use of Indirect Addressing ;(via FSR and INDF register) to ;implement a simple ;Light Sequencer. Recall that ;the INDF register (at locn ;0x00, 0x80, 0x100, 0x180) ;actually is no register at all, but ;rather it becomes whatever register ;whose addr is loaded into FSR ;(at locn 0x04, 0x84, 0x104, 0x184). If ;FSR contains 0x20, then writing to INDF ;to the register at 0x20, and reading ;from INDF reads from the register at 0x20. ; ;When SW on RA0 goes HIGH, ;4 LEDs connected to outputs ;RA1, RA2, RA3, and RA4 ;are sequenced according to ;entries in a table placed ;in RAM. ;************************** ECE331 PIC Assembly (KEH)

  20. list p=16F877A #include "p16F877A.inc" radix decimal CBLOCK 0x20 ;start allocating RAM at first free locn (0x20) count1 ;count1 = 0x20 count2 ;count2 = 0x21 count3 ;count3 = 0x22 iter_cnt ;inter_cnt = 0x23 seq_tbl: 10 ;table with 10 light pattern entries ;seq_tbl = 0x24 (starting adr of table) temp ;temp = 0x2E ENDC org 0 ;Reset vector is at prog loc 0x00. goto beginpgm ;Skip over INT vector at prog loc 0x04. org 0x05 ECE331 PIC Assembly (KEH)

  21. beginpgm banksel ADCON1 movlw 6 movwf ADCON1 banksel PORTA clrf PORTA ;initialize port A by zeroing ;output data latches. banksel TRISA movlw 0x01 ;Set RA0 for input, rest outputs movwf TRISA banksel PORTA ;switch back to bank 0 ECE331 PIC Assembly (KEH)

  22. ;*** initialize RAM table movlw B'0001' movwf seq_tbl+0 movlw B'0010' movwf seq_tbl+1 movlw B'0100' movwf seq_tbl+2 movlw B'1000' movwf seq_tbl+3 movlw B'1100' movwf seq_tbl+4 movlw B'1110' movwf seq_tbl+5 movlw B'1111' movwf seq_tbl+6 movlw B'0000' movwf seq_tbl+7 movlw B'1001' movwf seq_tbl+8 movlw B'0110' movwf seq_tbl+9 ECE331 PIC Assembly (KEH)

  23. waitsw btfss PORTA,0 ;check RA0 goto waitsw ;wait until switch on RA0 is UP. movlw 5 movwf iter_cnt wrap_to_top movlw seq_tbl ;initialize fsr reg to point to start of table movwf FSR get_next_pattern movf INDF,w ;get next light pattern from table movwf temp rlf temp,f ;rotate temp one bit to left, since LEDs are on RA1 - RA4 movf temp,w movwf PORTA ;put out new light pattern call wait_swloop incf FSR,f movf FSR,w sublw seq_tbl+10 btfss STATUS,2 ;Skip next instruction if Z = 1 goto get_next_pattern decfsz iter_cnt,f goto wrap_to_top done goto done ; ECE331 PIC Assembly (KEH)

  24. ;Subroutine wait_swloop -- delays about 1 second using nested sw loop ; wait_swloop movlw 80 movwf count1 loopout movwf count2 loopmid movwf count3 loopinr decfsz count3,f goto loopinr decfsz count2,f goto loopmid decfsz count1,f goto loopout return end ECE331 PIC Assembly (KEH)

  25. Ex 5. Light Show with Table in Program Memory ;Use of Lookup Table (in program memory) ;to implement a simple Light Sequencer. ; ;When SW on RA0 goes HIGH, 4 LEDs connected to outputs ;RA1, RA2, RA3, and RA4 are sequenced according to ;entries in a table placed in Program ROM ;************************** list p=16F877 #include "P16F877.inc" radix decimal CBLOCK 0x20 ;first free Reg File locn ;data locations 0x00 - 0x0B. count1 count2 count3 iter_cnt tbl_ptr temp ENDC ECE331 PIC Assembly (KEH)

  26. org 0 ;Reset vector is at prog loc 0x00. goto beginpgm ;Skip over INT vector at prog loc 0x04. org 0x05 beginpgm banksel ADCON1 movlw 6 movwf ADCON1 banksel PORTA clrf PORTA ;initialize port A by zeroing ;output data latches. banksel TRISA movlw 0x01 ;Set RA0 for input, RA1 for output movwf TRISA banksel PORTA ECE331 PIC Assembly (KEH)

  27. waitsw btfss PORTA,0 ;check RA0 goto waitsw ;wait until switch on RA0 is UP. movlw 5 movwf iter_cnt wrap_to_top movlw 0 movwf tbl_ptr get_next_pattern call pattern_subroutine movwf temp rlf temp,f ;rotate temp one bit to left, movf temp,w ;since LEDs are on RA1 - RA4 movwf PORTA ;put out new light pattern call wait_swloop incf tbl_ptr,f movf tbl_ptr,w sublw 10 btfss STATUS,2 ;Skip next instruction if Z = 1 goto get_next_pattern decfsz iter_cnt,f goto wrap_to_top done goto done ECE331 PIC Assembly (KEH)

  28. ;Subroutine wait_swloop -- delays about 1 second using nested sw loop wait_swloop movlw .80 movwf count1 loopout movwf count2 loopmid movwf count3 loopinr decfsz count3,f goto loopinr decfsz count2,f goto loopmid decfsz count1,f goto loopout return ;Pattern lookup table - part of program space the "Define Table" (DT) directive assembles ;a series of "retlw" instructions. The table below consists of retlw 1, retlw 2, retlw 4, retlw 8, ; etc. Upon return from this routine, w contains the looked up "light pattern" value. pattern_subroutine movf tbl_ptr,w addwf pcl,f ;compute index into table and jump there and execute ;the appropriate retlw instruction! seq_tbl dt B'0001',B'0010',B'0100',B'1000',B'1100',B'1110',B'1111',B'0000' dt B'1001',B'0110' end ECE331 PIC Assembly (KEH)

More Related