Fundamental of Assembly Language Programming (for Microprocessor) Prima Dewi Purnamasari Microprocessor Electrical Engineering Department Universitas Indonesia

Computer Language High Level language Low Level Language Machine Codes Pascal, C, C++, Java, etc Low Level Language Assembly Machine Codes 010010001010100101010  in binary 1234 FFAB 1234 H  in hexadecimal Microprocessor (c) Prima Dewi Purnamasari 2011

Why Assembly? Assembly has several features that make it a good choice many some situations. It's fast – Assembly programs are generally faster than programs created in higher level languages. Often, programmers write speed-essential functions in assembly. It's powerful – You are given unlimited power over your assembly programs. Sometimes, higher level languages have restrictions that make implementing certain things difficult. It's small – Assembly programs are often much smaller than programs written in other languages. This can be very useful if space is an issue. Microprocessor (c) Prima Dewi Purnamasari 2011

Preparation for Assembly Programming Basically you will need: Program editor  as simple as Notepad Assembler MASM  http://www.masm32.com/. TASM  Made by Borland, a commercial product NASM  http://sourceforge.net/projects/nasm/ Be careful in writing your programs, because it runs directly on your microprocessor! Microprocessor (c) Prima Dewi Purnamasari 2011

Steps to Create a Program Microprocessor (c) Prima Dewi Purnamasari 2011

MASM32 Microprocessor (c) Prima Dewi Purnamasari 2011

TASM Microprocessor (c) Prima Dewi Purnamasari 2011

Emulator an emulator is hardware and/or software that duplicates (or emulates) the functions of a first computer system in a different second computer system, so that the behavior of the second system closely resembles the behavior of the first system. Microprocessor (c) Prima Dewi Purnamasari 2011

Emu8086 Microprocessor (c) Prima Dewi Purnamasari 2011

Individual Assignment Download and install emu8086 (trial) http://www.emu8086.com/ Find corresponding tutorial on how to use it (available on the Internet!), self study! Microprocessor (c) Prima Dewi Purnamasari 2011

Group assignment Each group is responsible to bring at minimum 1 laptop (with emu8086 installed) to class every session Microprocessor (c) Prima Dewi Purnamasari 2011

Creating an Assembly Language Program An assembly language program should be written with any text editor and have the extension filename.asm. The assembler and Linker The assembler program converts a symbolic source module (file) into a hexadecimal object file The linker program executes as the second part of ML, reads the object files, created by the assembler program, and links them into a single execution file (.EXE) Microprocessor (c) Prima Dewi Purnamasari 2011

Microprocessor (c) Prima Dewi Purnamasari 2011

Assembly Program Structure Microprocessor (c) Prima Dewi Purnamasari 2011

Microprocessor (c) Prima Dewi Purnamasari 2011

LIST File, generated automatically after program successfully assembled MemoryAddress Machine codes Microprocessor (c) Prima Dewi Purnamasari 2011

NEXT: MOV AX, [BX] ; comment Writing Structure NEXT: MOV AX, [BX] ; comment 1= label, followed by “:” 2= opcode 3= operand 4= comment, preceded with”;” 1 2 3 4 Microprocessor (c) Prima Dewi Purnamasari 2011

Writing Structure Each statement in an assembly language program consists of four parts or fields. The leftmost field is called the label. used to store a symbolic name for the memory location it represents All labels must begin with a letter or one of the following special characters: @, $, -, or ?. a label may have any length from 1 to 35 characters The label appears in a program to identify the name of a memory location for storing data and for other purposes. Microprocessor (c) Prima Dewi Purnamasari 2011

The next field to the right is the opcode field. designed to hold the instruction, or opcode the MOV part of the move data instruction is an example of an opcode Right of the opcode field is the operand field. contains information used by the opcode the MOV AL,BL instruction has the opcode MOV and operands AL and BL The comment field, the final field, contains a comment about the instruction(s). comments always begin with a semicolon (;) Microprocessor (c) Prima Dewi Purnamasari 2011

Click “View” and look the changes in every menu list: Try it in emulator! Click “View” and look the changes in every menu list: registers Data Screen Flags etc Microprocessor (c) Prima Dewi Purnamasari 2011

Computer Data Formats Microprocessor (c) Prima Dewi Purnamasari 2011

Computer Data Formats ASCII and Unicode Data Binary Coded Decimal (BCD) Byte-Sized Data Word-Sized Data Doubleword-Sized Data Real Numbers Microprocessor (c) Prima Dewi Purnamasari 2011

ASCII Data American Standard Code for Information Interchange (ASCII) data represent alphanumeric characters in the memory of a computer system (Table 1.7) The standard ASCII code is a 7-bit code with the eighth and MSB used to hold parity in some systems ASCII are most often stored in memory using a special directive to the assembler program called define byte(s) or DB Microprocessor (c) Prima Dewi Purnamasari 2011

Microprocessor (c) Prima Dewi Purnamasari 2011

BCD Data Binary-Coded Decimal (BCD) information is stored in either packed or unpacked forms Packed BCD data are stored as two digits per byte Unpacked BCD data are stored as one digit per byte The range of a BCD digit extends from 00002 to 10012 or 0-9 decimal Table 1.9 shows some decimal numbers converted to both packed ad unpacked BCD Microprocessor (c) Prima Dewi Purnamasari 2011

Microprocessor (c) Prima Dewi Purnamasari 2011

Byte-Sized Data Byte-size data are stored as unsigned and signed integers Negative signed numbers are stored in the 2’s complement form Whenever a number is 2’s complement, its sign changes from negative to positive or positive to negative See example 1-22, 1-23 Microprocessor (c) Prima Dewi Purnamasari 2011

Microprocessor (c) Prima Dewi Purnamasari 2011

Define bit (DB) directive is used to store 8-bit data in memory Microprocessor (c) Prima Dewi Purnamasari 2011

Word-sized Data A word (16-bits) is formed with two bytes of data The LSB is always stored in the lowest-numbered memory location, the MSB in the highest (i.e., little endian format)— used with Intel family of microprocessor An alternate method (i.e., big endian format) is used with the Motorola family of micro-processors Microprocessor (c) Prima Dewi Purnamasari 2011

Word-sized Data Fig 1.11(a) & (b) shows the weight of each bit position in a word of data Microprocessor (c) Prima Dewi Purnamasari 2011

Microprocessor (c) Prima Dewi Purnamasari 2011

Example 1.25 shows several signed and unsigned word-sized data stored in memory using the assembler program Note that define word(s) directive or DW causes the assembler to store words in the memory Microprocessor (c) Prima Dewi Purnamasari 2011

Microprocessor (c) Prima Dewi Purnamasari 2011

Doubleword-sized Data Doubleword-sized data requires four bytes of memory (32-bit number) Doubleword-sized data appear as a product after a multiplication and also as a dividend before a division Fig. 1-12 shows the form used to store doublewords in the memory and the binary weights of each bit position Microprocessor (c) Prima Dewi Purnamasari 2011

Microprocessor (c) Prima Dewi Purnamasari 2011

To define doubleword-sized data, use assembler directive define doubleword or DD Microprocessor (c) Prima Dewi Purnamasari 2011

Real Numbers A real number (floating-point number) contains two parts: a mantissa, significant, or fraction and an exponent Fig. 1-13 and example 1-27 depicts both the 4-byte (single precision) and 8-byte (double precision) forms of real numbers Microprocessor (c) Prima Dewi Purnamasari 2011

Microprocessor (c) Prima Dewi Purnamasari 2011

The exponent is stored as a biased exponent an exponent of 23 is represented as a biased exponent of 127+3 or 130 (82H) in the single- precision form or as 1026 (402H) in the double-precision form Microprocessor (c) Prima Dewi Purnamasari 2011

Microprocessor (c) Prima Dewi Purnamasari 2011

Assembler detail From chapter 4 42 Microprocessor (c) Prima Dewi Purnamasari 2011 Microprocessor (c) Prima Dewi Purnamasari 2011

Directives Indicate how an operand or section of program is to be processed by the assembler Storing Data in a Memory Segment: DB, DW, DD, SEGMENT, .DATA, ENDS, DUP, ALIGN e.g.: Example 4.12 THIS refers the data as byte or word Microprocessor (c) Prima Dewi Purnamasari 2011

Memory is reserved for use in the future by using a question mark ( Memory is reserved for use in the future by using a question mark (?) as an operand for a DB, DW, or DD directive. when ? is used in place of a numeric or ASCII value, the assembler sets aside a location and does not initialize it to any specific value DUP: creates array with or without initial values It is important that word-sized data are placed at word boundaries and doubleword-sized data are placed at doubleword boundaries. if not, the microprocessor spends additional time accessing these data types Microprocessor (c) Prima Dewi Purnamasari 2011

Microprocessor (c) Prima Dewi Purnamasari 2011

EQU, ORG ASSUME Equate directive (EQU) equates a numeric, ASCII, or label to another label. equates make a program clearer and simplify debugging EX: TEN EQU 10 …. MOV AL,TEN The ORG (origin) statement changes the starting offset address of the data or code segments. At times, the origin of data or the code must be assigned to an absolute offset address with the ORG statement. ASSUME tells the assembler what names have been chosen for the code, data, extra, and stack segments. Used only with full-segment definition Microprocessor (c) Prima Dewi Purnamasari 2011

Microprocessor (c) Prima Dewi Purnamasari 2011

PROC and ENDP Indicate start and end of a procedure (subroutine). they force structure because the procedure is clearly defined Both the PROC and ENDP directives require a label to indicate the name of the procedure. RET instruction executed the end of the proc. USES directive indicates which registers are used by the proc. The assembler automatically save and restore them using the stack instructions. EX: PRC1 PROC USES AX BX CX Use .LISTALL directive to view all instruction generated by assembler Microprocessor (c) Prima Dewi Purnamasari 2011

Microprocessor (c) Prima Dewi Purnamasari 2011

Microprocessor (c) Prima Dewi Purnamasari 2011

The assembler uses two basic formats for developing software: Memory Organization The assembler uses two basic formats for developing software: one method uses models; the other uses full-segment definitions Memory models are unique to MASM. The models are easier to use for simple tasks. The full-segment definitions offer better control over the assembly language task and are recommended for complex programs. Microprocessor (c) Prima Dewi Purnamasari 2011

Models There are many models available to the MASM assembler, ranging from tiny to huge. .MODEL memsize TINY: all software and data fit into 64kb memory segment. Useful for small programs. assembled as a command (.COM) program SMALL: one data segment with one code segment for a total of 128kb of memory. assembled as an execute (.EXE) program Start of segments: .CODE, .DATA, .STACK Start of instructions and load segment registers with segment addresses: .STARTUP Exit to DOS: .EXIT End of file: END MP selection : .386, .486, .586, .686 .. Microprocessor (c) Prima Dewi Purnamasari 2011

Microprocessor (c) Prima Dewi Purnamasari 2011

Full Segment Definitions Full-segment definitions are also used with the Borland and Microsoft C/C++ environments for procedures developed in assembly language More structured form than the model method Use assume directive before the program begins. The program loader does not automatically initialize DS and ES. These registers must be loaded in the program STACK_SEG, DAT_SEG, CODE_SEG, END MAIN Microprocessor (c) Prima Dewi Purnamasari 2011

Microprocessor (c) Prima Dewi Purnamasari 2011 STACK_SEG SEGMENT ‘STACK’ DW 100H DUP(?) STACK_SEG ENDS DATA_SEG SEGMENT ‘DATA’ LISTA DB 100 DUP(?) LISTB DB 100 DUP(?) DATA_SEG ENDS COSE_SEG SEGMENT ‘CODE’ ASSUME CS:CODE_SEG, DS:DATA_SEG, SS:STACK_SEG MAIN PROC FAR MOV AX, DATA_SEG MOV ES, AX MOV DS, AX CLD MOV SI, OFFSET LISTA MOV DI, OFFSET LISTB MOV CX, 100 REP MOVSB MAIN ENDP CODE_SEG ENDS END MAIN Microprocessor (c) Prima Dewi Purnamasari 2011

Introduction to MOV Instruction Microprocessor (c) Prima Dewi Purnamasari 2011

Data Addressing Modes opcode an opcode, or operation code, tells the microprocessor which operation to perform MOV instruction provides a basis for explanation of data-addressing modes Microprocessor (c) Prima Dewi Purnamasari 2011

MOV Instruction MOV instruction perform COPY of a value, either from or to memory or register MOV = COPY MOV ≠ MOVE Microprocessor (c) Prima Dewi Purnamasari 2011

MOV BX, CX The source register’s contents do not change. the destination register’s contents do change The contents of the destination register or destination memory location change for all instructions except the CMP and TEST instructions. Note that only the rightmost 16 bits of register EBX change. The MOV BX, CX instruction does not affect the leftmost 16 bits of register EBX Microprocessor (c) Prima Dewi Purnamasari 2011

Some MOV Variant MOV AX,BX MOV [BX], AX MOV DATA,AX MOV AX,0123H [ ] sign represents memory location Destination = memory which has address as in BX MOV DATA,AX DATA is a name the programmer define in DATA SEGMENT destination=memory named DATA MOV AX,0123H a value 0123H is copied to AX register There are several more, but the above are the fundamental ones Microprocessor (c) Prima Dewi Purnamasari 2011

Rules in addressing. DO NOT: Mix different size of register MOV AX, BL Perform memory to memory addressing MOV [1234H],DATA Copy content of one segment register to another MOV DS,ES Use CS as the destination register MOV CS,1000H Microprocessor (c) Prima Dewi Purnamasari 2011

Group Assignment—Due Thursday 22/9 Make a program (altogether in one program, sequentially) Reserve place for data in data segment namely DATA1 with type word Copy 1234 to AX Copy 0011B to AL Copy 12H to AH Copy AX to DATA1 Microprocessor (c) Prima Dewi Purnamasari 2011

The report Write the program in emulator Compile it. Run the program in emulator. (single step). Analyze the effect on the registers and memory for each line of code Written report should be made as comprehensive as it can be (greater score for better report) The main part of your report would be: Print of program (source code), provide sufficient comment Print of LISTING file Program analysis Microprocessor (c) Prima Dewi Purnamasari 2011