TK 2123

1. TK 2123 Lecture 13: Assembly Language Level (Level 4)

2. Why Use Assembly Language? • Assembly language programming is difficult. • Writing a program in assembly language takes much longer than writing the same program in a high-level language. • Much longer to debug and much harder to maintain. • Why use assembly language? • Performance • Access to the machine Prepared by: Dr Masri Ayob

3. Why Use Assembly Language? • Performance • An expert assembly language programmer can often produce code that is much smaller and faster than a high-level language programmer can. • Some application – speed and size are critical. E.g. embedded application (code on a smart card, handphone, etc.) • Access to the machine. • Some procedure need complete access to the hardware. • E.g. low-level interrupt, trap handlers in OS, device controller, etc. • This is usually impossible in high-level language. Prepared by: Dr Masri Ayob

4. Why Use Assembly Language? Comparison of assembly language and high-level language programming, with and without tuning. Prepared by: Dr Masri Ayob

5. Assembly Language • Assembly language: • Assembly language is used for most programming because it is extremely difficult to program a microprocessor in its native, that is hexadecimal machine language. • Assembler: • An assembler is a program that converts software written in symbolic machine language (the source program) into hexadecimal machine language (object program). • The primary reason to use assembler is because development and modification are always difficult in machine language. Prepared by: Dr Masri Ayob

6. Assembly Language • Instruction is a command to the microprocessor to perform a given task on specified data. • Each instruction has two parts: • one is the task to be performed, called the operation code (op-code), • the second is the data to be operated on, called the operand. • The operand (or data) can be specified in various ways. • It may include an internal register or a memory location. • In some instructions, the operand is implicit. Prepared by: Dr Masri Ayob

7. Assembly Language • The Two-pass Assembler : • Read programme two times. • Generate a table of the labels/symbols within the source program. • Develop hexadecimal version of the source program. • Allow forward addressing (the software can jump ahead to an instruction in a program). Prepared by: Dr Masri Ayob

8. Assembly Language Prepared by: Dr Masri Ayob

9. Assembly Language • The assembler always assumes that the first instruction of the program is stored at memory address 0000H unless otherwise directed by the ORG command. Prepared by: Dr Masri Ayob

10. Assembly Language • Pass One: • The assembler scans the source program during the first pass and generates a table of the labels found within the source program. • Each entry in the label table contains the label and the address where the label appears in the program. • During the first pass the assembler determines the length of each instruction by updating an internal program counter. • This internal program counter allows the assembler to complete the label table by equating each label with the counter. • Once the label table is complete the second pass begin. Prepared by: Dr Masri Ayob

11. Assembly Language • Pass Two: • During the second pass of the source program, the assembler forms the object program. • This occurs by referring to the label table for any labels that appear in the program and to an instruction table. • The instruction table contains all the opcodes in both symbolic and machine language forms. • The tables help convert the source program into the object program. Prepared by: Dr Masri Ayob

12. Assembly Language • Assembly Language Statement: • Format : • Label Field. • Contains a symbolic memory address that refers to the statement in a program. Labels are optional. • Labels are constructed from alphanumeric characters and must begin with any letter of the alphabet. Prepared by: Dr Masri Ayob

13. Format of an Assembly Language Statement (1) Computation of N = I + J. (a) Pentium 4. Prepared by: Dr Masri Ayob

14. Format of an Assembly Language Statement (2) Computation of N = I + J. (b) Motorola 680x0. Prepared by: Dr Masri Ayob

15. Format of an Assembly Language Statement (3) Computation of N = I + J. (c) SPARC. Prepared by: Dr Masri Ayob

16. Assembly Language • Opcode field: • This field must contain opcodes. • Operand field: • May contain register name, data or labels. • If more than one of these is present, they must be separated with comma. • Data must be encoded as decimal, binary, octal, hexadecimal, or ASCII. • ASCII must appear as one of more letters surrounded by apostrophe. Prepared by: Dr Masri Ayob

17. Assembly Language • Operand arithmetic operations. Prepared by: Dr Masri Ayob

18. Assembly Language • Comment field. • Must begin with semicolon in most 8085 assemblers and may continue to the end of the line only. • Use asterisk * or semicolon ; if the comment should continue into the next line. • Example : Prepared by: Dr Masri Ayob

19. Pseudoinstructions • Assembler pseudo operations. • Directives to the assembler program that may or may not generate machine code. • Examples : • END, DB, DW, DS, ORG, EQU, IF, ENDIF, SET, GLB, EXT, TITLE, SPC. • All pseudo operations must appear in the opcode field of a statement. Prepared by: Dr Masri Ayob

20. Pseudoinstructions • Define Byte (DB). • Defines 8-bit memory data for a program. • Multiple one byte data, comma ( , ) as a separator. Prepared by: Dr Masri Ayob

21. Assembly Language : Example Prepared by: Dr Masri Ayob

22. Pseudoinstructions • Origin (ORG). • Changes the starting location of the program to another address besides 0000H. • Can be used at any place in a program to change the location of the assembled machine language instructions or data. Prepared by: Dr Masri Ayob

23. Assembly Language : Example Prepared by: Dr Masri Ayob

24. Pseudoinstructions • Define Word (DW). • Pseudo operation stores a 16-bit number in the memory for use by a program. • Defines no only numeric data but also memory addresses and label. Prepared by: Dr Masri Ayob

25. Assembly Language : Example Prepared by: Dr Masri Ayob

26. Pseudoinstructions • Define Storage (DS). • Reserves space in a program for variable data. • Does not place any specific data into the reserved area of memory. Prepared by: Dr Masri Ayob

27. Assembly Language : Example Prepared by: Dr Masri Ayob

28. Pseudoinstructions • Equate (Equ). • Equates a label to another label or value. • Note that the EQU statement label does not contain a colon ( : ). Prepared by: Dr Masri Ayob

29. Assembly Language Prepared by: Dr Masri Ayob

30. Macro • Assembly language programmer frequently need to repeat sequence of instructions several times within a program. • Solution: • Use subroutine (CALL instruction). • Disadvantage: Procedure CALL overhead. • Use Macro • Easy and efficient solution • Is a way to give name to a piece of text. Prepared by: Dr Masri Ayob

31. Macro Definition, Call, Expansion (1) Assembly language code for interchanging P and Q twice. (a) Without a macro. (b) With a macro. Macro Prepared by: Dr Masri Ayob

32. Macro Definition, Call, Expansion (2) Comparison of macro calls with procedure calls. Prepared by: Dr Masri Ayob

33. Macros with Parameters Nearly identical sequences of statements. (a) Without a macro. (b) With a macro. Prepared by: Dr Masri Ayob

34. Thank youQ&A Prepared by: Dr Masri Ayob