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16.317: Microprocessor System Design I

16.317: Microprocessor System Design I. Instructor: Dr. Michael Geiger Spring 2012 Lecture 32: PIC instruction set, pt. 2. Lecture outline. Announcements/reminders Lab 4 due 4/25 Limited # of PICkits  strongly suggest you work in a group for the last two assignments

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16.317: Microprocessor System Design I

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  1. 16.317: Microprocessor System Design I Instructor: Dr. Michael Geiger Spring 2012 Lecture 32: PIC instruction set, pt. 2

  2. Lecture outline • Announcements/reminders • Lab 4 due 4/25 • Limited # of PICkits strongly suggest you work in a group for the last two assignments • PICkits can be checked out from the lab • Lab 5, HW 4 to be posted ASAP (hopefully later today) • Lecture outline • Review: PIC instructions • Formats • Variables • Clear/move • Unary ops • Arithmetic • PIC instructions • Logical ops • Goto/call/return • Misc Microprocessors I: Lecture 32

  3. Review: PIC instructions • Four instruction formats • Upper bits of all hold opcode • Byte-oriented includes 1 bit destination, 7 bit direct address • Bit-oriented includes 3 bit position (0-7), 7 bit direct address • Literal/control includes 8 bit literal • CALL/GOTO includes 11 bit literal • Variable declarations • cblock <start_address>: start of variable declarations • All names between cblock/endc directives assigned to consecutive bytes starting at <start_address> Microprocessors I: Lecture 32

  4. Review: PIC instructions (cont.) • Clearing register: clrw/clrf • Moving values: movlw/movwf/movf • Swap nibbles: swapf • Single bit manipulation: bsf/bcf • Unary operations: incf/decf/comf • Arithmetic: addlw/addwf/sublw/subwf Microprocessors I: Lecture 32

  5. Example • Show the values of all changed registers after the following sequence cblock0x20 varA varB varC endc clrfvarA clrfvarB clrfvarC incfvarA, W sublw 0x0F addwfvarB, F decfvarB, F comfvarB, W subwfvarC, F Microprocessors I: Lecture 32

  6. Example solution clrfvarA varA = 0 clrfvarB varB= 0 clrfvarC varC= 0 incfvarA, W  W = varA + 1 = 1 sublw 0x0F  W = 0x0F – W = 0x0F – 1 = 0x0E addwfvarB, F  varB = varB + W = 0x0E decfvarB, F  varB = varB – 1 = 0x0D comfvarB, W  W= ~varB = ~0x0D = 0xF2 subwfvarC, F  varC = varC – W Microprocessors I: Lecture 31

  7. Multi-bit Manipulation Examples: • andlw B’00000111’ ;force upper 5 bits of W to zero • andwf TEMP1, F ;TEMP1 <- TEMP1 AND W • andwf TEMP1, W ;W <- TEMP1 AND W • iorlw B’00000111’ ;force lower 3 bits of W to one • iorwf TEMP1, F ;TEMP1 <- TEMP1 OR W • xorlw B’00000111’ ;complement lower 3 bits of W • xorwf TEMP1, W ;W <- TEMP1 XOR W andlw k ; AND literal value k into W andwf f, F(W) ; AND W with F, putting result in F or W iorlw k ; Inclusive-OR literal value k into W iorwf f, F(W) ; Inclusive-OR W with F, putting result in F or W xorlw k ; Exclusive-OR literal value k into W xorwf f, F(W) ; Exclusive-OR W with F, putting result in F or W STATUS bits: Z Microprocessors I: Lecture 32

  8. Rotate Examples: • rlf TEMP1, F ; C <- TEMP1.bit(7), TEMP1.bit(i+1) <- TEMP1.bit(i) ; TEMP1.bit(0) <- C • rrf TEMP1, W ; Copy TEMP1 to W and rotate W right through C ; TEMP1 unchanged rlf f, F(W) ; copy f into F or W; rotate F or W left through ; the carry bit rrf f, F(W) ; copy f into F or W; rotate F or W right through ; the carry bit STATUS bits: C Microprocessors I: Lecture 32

  9. Example • Show the values of all changed registers after the following sequence • Assume the carry bit is initially 0 cblock0x40 z endc clrf z movlw 0xF0 iorwf z, F xorlw 0xFF rrf z, F andwf z, W rlf z, F Microprocessors I: Lecture 32

  10. Example solution clrf z  z = 0 movlw 0xF0  W = 0xF0 iorwf z, F  z = z OR W = 0xF0 xorlw 0xFF  W = W XOR 0xFF = 0xF0 XOR 0xFF = 0x0F rrf z, F  Rotate z right thru carry Before rotate, (z, carry) = 1111 0000 02  z = 0111 10002 = 0xE8, C = 0 andwf z, W  W = z AND W = 0xE8 AND 0x0F = 0x08 rlf z, F  Rotate z left thru carry Before rotate, (z, carry) = 0 0111 10002  z = 1111 00002 = 0xF0, C = 0 Microprocessors I: Lecture 32

  11. Goto/Call/Return/Return from Interrupt Examples: • goto There ; Next instruction to be executed is labeled “There” • call Task1 ; Push return address; Next instruction to be ; executed is labeled “Task1” • return ; Pop return address off of stack • retlw 5 ; Pop return address; W <- 5 • retfie ; Pop return address; re-enable interrupts goto label ; Go to labeled instruction call label ; Call labeled subroutine return ; Return from subroutine retlw k ; Return from subroutine, putting literal ; value in W retfie ; Return from interrupt service routine; ; re-enable interrupts STATUS bits: none Microprocessors I: Lecture 32

  12. Miscellaneous Examples: • clrwdt ; if watchdog timer is enabled, this instruction will reset ; it (before it resets the CPU) • sleep ; Stop clock; reduce power; wait for watchdog timer or ; external signal to begin program execution again • nop ; Do nothing; wait one clock cycle clrwdt ; clear watchdog timer sleep ; go into standby mode nop ; no operation STATUS bits: clrwwdt, sleep: NOT_TO, NOT_PD nop: none Microprocessors I: Lecture 32

  13. Next time • Continue with discussion of PIC instructions Microprocessors I: Lecture 32

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