1. Microprocessor MA Rahim Khan Computer Engineering and Networks Department

2. Flag Register Carry Flag (CF) - this flag is set to 1 when there is an unsigned overflow. For example when you add bytes 255 + 1 (result is not in range 0...255). When there is no overflow this flag is set to 0. Zero Flag (ZF) - set to 1 when result is zero. For none zero result this flag is set to 0. Sign Flag (SF) - set to 1 when result is negative. When result is positive it is set to 0. Actually this flag take the value of the most significant bit. Overflow Flag (OF) - set to 1 when there is a signed overflow. For example, when you add bytes 100 + 50 (result is not in range -128...127).

3. Flag Register Cont…. Parity Flag (PF) - this flag is set to 1 when there is even number of one bits in result, and to 0 when there is odd number of one bits. Even if result is a word only 8 low bits are analyzed! Auxiliary Flag (AF) - set to 1 when there is an unsigned overflow for low nibble (4 bits). Interrupt enable Flag (IF) - when this flag is set to 1 CPU reacts to interrupts from external devices. Direction Flag (DF) - this flag is used by some instructions to process data chains, when this flag is set to 0 - the processing is done forward, when this flag is set to 1 the processing is done backward.

4. Carry Flag include 'emu8086.inc' ORG 100h MOV AL, 255 ADD AL, 1 JC label1 PRINT 'no carry.' JMP exit label1: PRINT 'has carry.' exit: RET

5. Jump if CX Register is Zero include 'emu8086.inc' ORG 100h MOV CX, 0 JCXZ label1 PRINT 'CX is not zero.' JMP exit label1: PRINT 'CX is zero.' exit: RET

6. Jump if Parity Even include 'emu8086.inc' #make_com# ORG 100h MOV AL, 00000101b ; AL = 5 AND AL, 11111111B ; just set flags. JP label1 PRINT 'parity odd.' JMP exit label1: PRINT 'parity even.' exit: RET

7. Jump if Parity Even include 'emu8086.inc' ORG 100h MOV AL, 00000101b ; AL = 5 OR AL, 0 ; just set flags. JPE label1 PRINT 'parity odd.' JMP exit label1: PRINT 'parity even.' exit: RET

8. Jump if Parity Odd. include 'emu8086.inc' ORG 100h MOV AL, 00000111b ; AL = 7 OR AL, 0 ; just set flags. JPO label1 PRINT 'parity even.' JMP exit label1: PRINT 'parity odd.' exit: RET

9. Jump if Signed include 'emu8086.inc' ORG 100h MOV AL, 10000000b ; AL = -128 OR AL, 0 ; just set flags. JS label1 PRINT 'not signed.' JMP exit label1: PRINT 'signed.' exit: RET

10. Jump if Not Signed ORG 100h MOV AL, 00000111b ; AL = 7 OR AL, 0 ; just set flags. JNS label1 PRINT 'signed.' JMP exit label1: PRINT 'not signed.' exit: RET

11. Complement Carry flag(CMC) if CF = 1 then CF = 0 if CF = 0 then CF = 1 No operands

12. Clear Carry flag(CLC) Clear Carry flag. Algorithm: CF = 0 No operands

13. Signed divide.(IDIV) Signed divide. Algorithm: when operand is a byte: AL = AX / operand AH = remainder (modulus)when operand is a word: AX = (DX AX) / operand DX = remainder (modulus) Example: MOV AX, -203 ; AX = 0FF35h MOV BL, 4 IDIV BL ; AL = -50 (0CEh), AH = -3 (0FDh) RET

14. Signed Multiply when operand is a byte: AX = AL * operand. when operand is a word: (DX AX) = AX * operand. Example: MOV AL, -2 MOV BL, -4 IMUL BL ; AX = 8 RET