PIC Architecture: Instruction Set and Move Instructions, Slides of Microcomputers

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PIC Architecture

Instruction Set

PICs-Instruction Set

• Have Covered Instruction Set Basics
  • Accumulator Architecture
  • Direct addressing
  • Indirect addressing
• Now lets look at the instructions

More on MOVE

• Initialization of a variable
  • movlw B’11100000’
  • movwf TRIST
  • Initialize the PORTB data direction register
• Assembler MACRO
  • MOVLF B’11100000’,TRISB
  • Assembled into the two instructions above

The movff instruction

• movff PORTB, PORTB_COPY
  • movff - a two-word instruction
  • Thus source and destination have 12-bit addresses
    • Source – instruction bits + BSR
    • Destination – instruction 2nd^ byte
  • Moves data from a 1-byte source to a 1-byte destination.
  • For instruction memory as efficient as the regular move instruction.

The movf instruction

• Move the value and set the status register bits appropriately
• Affects N and Z bits

Move summary

• movlw k - load literal value
• movwf MYVAR - move value but do not affect status bits
• movff V1,V2 - move data at source address to data at destination address
• movf f,F/W - move value and affect status bits - What does movf COUNT,F do?

Load BSR register & other

• movlb 2
  • Load the value of 2 into the BSR register
• clrf TEMP – Load 0x00 into variable TEMP
• setf TEMP – Load 0xff into variable TEMP
• swapf f - swap nibbles of f

Single operand instructions

• Single bit instructions
  • bsf PORTB,0 - Set the lsb of PORTB
  • bcf PORTB,1 - clear bit 1 of PORTB
  • btg PORTB,2 - toggle bit 2 of PORTB
• Rotate instructions illustrated on next slide
  • rlcf rlncf rrcf rrncf
  • cf rotate including carry bit
  • ncf rotate without carry bit

Logical instructions

• andlw B’00001111’ And WREG with value
• andwf f,F/W - AND WREG with f putting result back in F or WREG
• iorlw k -Inclusive OR literal value and WREG
• iorwf f,F/W – inclusive OR WREG with f and put result into f or WREG
• xorlw k, xorwf f,F/W - Exclusive OR

Arithmetic

• addlw k, addwf f,F/W
• addwfc f,F/W - Add WREG, F and carry bit
• daw – Decimal adjust sum of pack BCD
• subwf, sublw
• subwfb f,F/W - subtract with borrow

Branches

• Needed for program flow control
• Tests on status register
  • bc, bnc, bz, bnz, bn, bnn, bov, bnov
  • Use the c, x, n, and ov bits of the status register
• bra – branch always

Conditional Skip instructions

• Ten further instructions that test for a condition and skip over the next instruction if the condition is met. - Next instruction is typically a branch or rcall - Very useful at end of a loop - Loop code …. - decfsz count,F ;Decrement and skip if zero - bra top_of_loop

Other – Subroutine, interrupt

• rcall label - call subroutine (within 512 instr)
• call label – call subroutine (anywhere)
• call label, FAST - call subroutine, copy state to shadow registers
• return – return form subroutine
• return FAST - return and restore from shadow registers
• return k - return and put value k in WREG

cont

• retfie - return from interrupt and re-enable
• retfie FAST – return, re-enable- restore
• push - Push addr of next instruction onto stack
• pop - discard address on top of stack
• clrwdt - clear watchdog timer
• sleep - Go into standby mode
• reset - software controlled reset
• nop