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16.317 Microprocessor Systems Design I

In this lecture, Dr. Michael Geiger explores arithmetic instructions fundamental to microprocessor design. Key topics include data transfer instructions (MOVSX, MOVZX, XCHG, LEA), various arithmetic operations (addition, subtraction, multiplication, division), and their corresponding flags (CF, OF, ZF, SF, PF, AF). The lecture provides practical examples using the ADD, SUB, and multiplications, illustrating how to calculate the results of sequences involving register and memory interactions. Students are reminded of homework due dates and upcoming labs.

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16.317 Microprocessor Systems Design I

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  1. 16.317Microprocessor Systems Design I Instructor: Dr. Michael Geiger Spring 2013 Lecture 7: Arithmetic instructions

  2. Lecture outline • Announcements/reminders • HW 1 due Friday, 2/8 • HW 2, Lab 1 coming soon • Review • Data transfer: MOVSX/MOVZX/XCHG/LEA/Lxx • Today’s lecture • Arithmetic instructions Microprocessors I: Lecture 7

  3. Review • MOVSX/MOVZX • Sign-extend or zero-extend register/memory value • XCHG • Exchange contents of source, dest • LEA: load effective address • Calculate EA/store in register • Load full pointer (LDS/LES/LFS/LGS/LSS) • Load dest & segment register from memory Microprocessors I: Lecture 7

  4. Arithmetic instructions • Addition • ADD • ADC • INC • Subtraction • SUB • SBB • DEC • NEG • Multiplication/division • MUL • IMUL • DIV • IDIV Microprocessors I: Lecture 7

  5. Flags • All arithmetic instructions set flags • CF = carry flag (carry output from MSB of add/sub) • OF = overflow flag • ZF = zero flag (result is zero) • SF = sign flag (1 if negative, 0 if positive) • PF = parity flag (even parity in LSB) • AF = auxiliary carry (carry between nibbles) • Stored in FLAGS register • Referenced in conditional instructions Microprocessors I: Lecture 7

  6. Addition instructions • ADD D, S • Operation: (D) = (D) + (S) • ADC D, S • Operation: (D) = (D) + (S) + (CF) • INC D • Operation: (D) = (D) + 1 Microprocessors I: Lecture 7

  7. Subtraction instructions • SUB D, S • Operation: (D) = (D) – (S) • SBB D, S • Operation: (D) = (D) – (S) – (CF) • DEC D • Operation: (D) = (D) – 1 • NEG D • Operation: (D) = -(D) • Two’s complement negation Microprocessors I: Lecture 7

  8. Addition/subtraction examples • Given the following initial state: • AX = 1234H • BL = ABH • Memory location SUM = 00CDH • Show the results of each step of the following instruction sequences: • ADD AX, [SUM] • ADC BL, 05H • NEG BL • SUB AX, 12H • INC WORD PTR [SUM] Microprocessors I: Lecture 7

  9. Example solution • ADD AX, [SUM] • (AX) = (DS:SUM) + (AX) • 00CDH + 1234H = 1301H • (AX) = 1301H, (CF) = 0 • ADC BL,05H • (BL) = (BL) + IMM8 +(CF) • ABH + 05H + 0 = B0H • (BL) = B0H, (CF) = 0 • NEG BL • (BL) = –(BL) • –B0H = –(1011 0000)2 = 0101 00002 = 50H Microprocessors I: Lecture 7

  10. Example solution (cont.) • SUB AX, 12H • (AX) = (AX) – 0012H • 1301H – 0012H = 12EFH • (AX) = 12EFH, (CF) = 0 • INC WORD PTR [SUM] • (DS:SUM) = (DS:SUM) + 1 • 00CDH + 1 = 00CEH • (SUM) = 00CEH, (CF) = 0 Microprocessors I: Lecture 7

  11. Multiplication/division • Both signed and unsigned integer versions • Register A is always one of the sources • Destination always same; size-dependent • Exception: signed multiplication does allow for slightly different operation • Easiest way to evaluate instructions: figure out decimal values of operands, do operation in decimal, then figure out binary/hex values of results Microprocessors I: Lecture 4

  12. MUL/IMUL • MUL S  unsigned multiplication • IMUL S  signed multiplication • Byte: (AX) = (AL) * (S) • Word: (DX,AX) = (AX) * (S) • Double-word: (EDX,EAX) = (EAX) * (S) • Only CF, OF updated Microprocessors I: Lecture 4

  13. DIV/IDIV • DIV S  unsigned division • IDIV S  signed division • Result split into quotient, remainder • Byte: (AL) = (AX) / (S) (AH) = (AX) % (S) • Word: (AX) = (DX,AX) / (S) (DX) = (DX,AX) % (S) • Dword: (EAX) = (EDX,EAX) / (S) (EDX) = (EDX,EAX) % (S) • Special “convert” instructions used to sign-extend value in register A before division Microprocessors I: Lecture 4

  14. Final notes • Next time: Continue with instructions • Reminders: • HW 1 due Friday, 2/8 • HW 2, Lab 1 coming soon Microprocessors I: Lecture 7

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