Microprocessor and assambly language programming
- 3. TEAM :ABRACADABRA 1. Afnanul Hassan #161-15- 7213 2. Khaled Akram Sany #161-15- 7203 3.Shami Al Rahad #161-15- 7349 4. Md. Sohanur Rahman Sakib #161-
- 4. WHAT IS MICROCOMPUTER? • System Bus Microproc essor ROM RAM input output Memory Element I/O unit
- 5. THE MICROPROCESSOR AND ITS ARCHITECTURE •ALU (Arithmetic and Logic Unit) •The Control Unit •Registers HDD RAM Cache Memory Microprocessor R1 R1 R3
- 6. THE PROGRAMMING MODEL •Program visible registers •We can access via programs •Program invisible registers •We can not access via programs
- 7. REGISTERS 16 bit Segment registers
- 8. EXAMPLE DATA • If AX = 20A2H then AH = 20H, AL = A2H • In other words, if AH = 1CH and AL = A2H then AX = 1CA2H 0010 0000 1010 0010 AH AL AX
- 9. THE FLAGS REGISTER • FLAGS indicate the condition of the MP • Also control the operations • FLAGS are upward compatible from 8086/8088 to Pentium/Pentium Pro Figure 2.2: The EFLAG and FLAG registers
- 10. THE FLAGS • Carry Flag – C • C = 1 if there is a carry out from the msb on addition • Or, there is a borrow into the msb on subtraction • Otherwise C = 0 • C flag is also affected by shift and rotate instructions 10101010 11101010 111010100 C = 1, in this case
- 11. THE FLAGS • Parity Flag – P • P = 1 for even parity, if number contains even number of ones • P = 0 for odd parity, if odd number of ones 10101010 10101011 P = 1 P = 0 Even number of ones Odd number of ones Definition changes from microprocessor to microprocessor
- 12. THE FLAGS • Zero Flag – Z • Z = 1 for zero result • Z = 0 for non-zero result • Sign Flag – S – S = 1 if msb of a result is 1, means negative number – S = 0 if msb of a result is 0, means positive number
- 13. THE FLAGS • Trap Flag – T • Enables trapping through an on-chip debugging feature • T = 1 MP interrupts the flow of a program, i.e. debug mode is enabled • T = 0 debug mode is disabled • Direction Flag – D – Selects increment/decrement mode of SI and/or DI registers during string instructions – D = 1, decrement mode, STD (set direction) instruction used – D = 0, increment mode, CLD (clear direction)
- 14. THE FLAGS • Overflow Flag – O • O = 1 if signed overflow occurred • O = 0 otherwise • Overflow is associated with the fact of range of numbers represented in a computer • 8 bit unsigned number range (0 to 255) • 8 bit signed number range (-128 to 127) • 16 bit unsigned number range (0 to 65535) • 16 bit signed number range (-32768 to 32767)
- 15. SIGNED VS. UNSIGNED OVERFLOW • Let, AX = FFFFh, BX = 0001h and execute • ADD AX, BX 1111 1111 1111 1111 + 0000 0000 0000 0001 1 0000 0000 0000 0000 AX BX • Unsigned interpretation – Correct answer is 10000h = 65536 – But this is out of range. – 1 is carried out of msb, AX = 0000h, which is wrong – Unsigned overflow occured • Signed interpretation – FFFFh = -1, 0001h = 1, summation is -1+1 = 0
- 16. HOW INSTRUCTIONS AFFECT THE FLAGS? • Every time the processor executes a instruction, the flags are altered to reflect the result • Let us take the following flags and instructions • Sign Flag – S • Parity Flag – P • Zero Flag – Z • Carry Flag – C • MOV/XCH G • ADD/SUB • INC/DEC • NEG None All All except C All (C = 1 unless result is 0)
- 17. EXAMPLE 1 • Let AX = FFFFh, BX = FFFFh and execute ADD AX, BX FFFFh + FFFFh 1 FFFEh The result stored in AX is FFFEh = 1111 1111 1111 1110 S P Z C = 1 because the msb is 1 = 0 because the are 15 of 1 bits, odd parity = 0 because the result is non-zero = 1 because there is a carry out of the msb on addition
- 18. EXAMPLE 2 • Let AX = 8000h, BX = 0001h and execute SUB AX, BX 8000h - 0001h 7FFFh The result stored in AX is 7FFFh = 0111 1111 1111 1111 S P Z C = 0 because the msb is 0 = 0 because the are 15 of 1 bits, odd parity = 0 because the result is non-zero = 0 because there is no carry
- 19. SEGMENT REGISTERS 16 bit Segment registers * * * Segment 1 Segment 2 Segment n 0000hCS 8000hDS A000hSS Fig:The programming model of intel 8086 trough the Pentium pro