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Mid-term Exam

Mid-term Exam. Basics & intuitive All materials till-to-date – very simple! Ref. book – Assembly Language Programming and Organization of the IBM PC, by Y. Yu & C. Marut Written exam. Smile – though your heart is breaking! Enjoy with study!. 4.7 Program Structure.

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Mid-term Exam

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  1. Mid-term Exam • Basics & intuitive • All materials till-to-date – very simple! • Ref. book – Assembly Language Programming and Organization of the IBM PC, by Y. Yu & C. Marut • Written exam

  2. Smile – though your heart is breaking! Enjoy with study!

  3. 4.7 Program Structure • Machine langprogs consist of • Code • Data • Stack • Each part occupies a memory segment

  4. 4.7.1 Mem Models • .MODEL memory_model ; directive • Mem. Models  • SMALL  Code in 1 segment, data in 1 seg. • MEDIUM  Code in 1+ seg, data in 1 seg • COMPACT … • LARGE …array in max. 64KB • HUGE

  5. Data segment • Contains all the variable definitions • Const. definitions too in most cases [cost. defn – no memory is involved, so anywhere] .DATA directive .DATA HASINA DW 2 KHALEDA DW 5 ERSHAD EQU 10010001b ;named constants – equates

  6. Stack segment • To set a block of memory to store the stack .STACK size ; max stack size ; sizeis optional no. .STACK 100H ; sets 100h Bytes for the stack area. ; if no size is mentioned – 1 KB is assigned

  7. Code segment • Contains a program’s instructions .CODE name ; name is optional ; NO need for name in SMALL program • Insides a code segment – instructions are organized as procedures.

  8. A simple procedure name PROC ; body of the procedure name ENDP; end procedure

  9. Defn. of a CODE segment .CODE MAIN PROC ; main procedure instructions MAIN ENDP ; other procedures go here

  10. …together! A typical form for SMALL model .MODEL SMALL .STACK 100h .DATA ;data definitions go here .CODE ;SMALL – so no name MAIN PROC ;instructions go here MAIN ENDP ;other instructions go here END MAIN

  11. 4.8 I/O Instructions • Instructions to access I/O ports directly – • IN • OUT ; provides first I/O ; less used

  12. 2 types of I/O service routines – • BIOS [Basic I/O System] routines  BIOS routines r stored in ROM,  interact directly with the I/O ports  see chap. 12. 2. DOS [Disk OS] routines  can do more complex tasks

  13. INT instruction • To invoke a DOS or BIOS routine – INT[Interrupt] instruction is used. • Interrupt A signal to a computer that stops the execution of a running program so that another action can be performed. INT int_no.

  14. INT int_no. • int_no.  is a number that specifies a routine INT 16h  invokes a BIOS routine that performs keyboard input • Chap. 15 for more INT 21h  invokes a large no. of DOS functions • Appendix C for more

  15. INT 21h(invokes no. of DOS functions) • A particular function is requested by placing a function no. in the AH register & • invoke INT 21h Function No. Routine 1 single-key input 2 single-character output 9 character string output

  16. INT 21h functions expect input values to be in certain reg. & return output in other reg. Function 1: Single-key input Input: AH = 1 Output: AL = ASCII code if character key is pressed = 0 if non-character key is pressed

  17. Function 2: Single-character output / control func. Input: AH = 2 DL = ASCII code of the display char or control char Output: AL = ASCII code of the display char or control char Function 2: Some control functions ASCII Symbol Function 7 BEL beep sound 8 BS backspace 9 HT tab …

  18. 1st prog! Q: Read a char – from a keyboard & display it at the beginning of the next line!

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