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

2. Display a question mark: MOV AH, 2 ;display character fn. – p
Display a question mark: MOV AH, 2 ;display character fn. – p.456  DOS Interrupts – Function 2h  display output to standard output device I/P: AH = 02h o/p: DL = character

3. MOV DL, ‘?’ ; char is ‘?’
It moves 3Fh [‘?’] into DL
INT 21h ; display character 
Next read a char.
MOV AH, 1 ; read char fn
Fn 1h  Keyboard input
INT 21h ; char in AL

4. Now display the char on the next line: [the char MUST be saved in another register] MOV BL, AL ; save it in BL Why? We move the input character from AL to BL – as the INT 21h, function 2  changes AL.

5. To move the cursor to the beginning of the next line, we must execute a carriage return and line feed. So, put the ASCII codes for them in DL and execute INT 21h MOV AH, 2 ; display char fn [আগের] MOV DL, 0Dh ; for carriage return INT 21h ; execute carr ret. MOV DL, 0Ah ; for line feed INT 21h ; execute line feed

6. So full prog
TITLE Echo prog .MODEL SMALL .STACK 100h .CODE MAIN PROC ; make a comment for a block MOV AH, 2 ; display char func … ; another block… ; return to DOS MOV AH, 4Ch ; DOS exit func INT 21h ; exit to DOS MAIN ENDP END MAIN

7. RUN!
Create the source program file – in a word proc/text/… [*.asm file]
Assemble the prog using an Assembler [*.obj file]
Link object program – to link one or more obj files to create a run file [*.exe file]

8. Do/Read
4.11 Displaying a string INT 21h , Function 1  to read a single char Function 2  to display a single char Function 9  to display a string Input: DX = offset address of string The string must end with a ‘$’ char

9. LEA LEA – Load Effective Address
- puts a copy of the source offset address into the dest.
LEA DX, MSG
- Puts the offset address of the variable MSG into DX

10. Read
4.12 A case conversion prog. lowercase to UPPER UPPER to lover Chapter 4 – finish the exercises Chapter 5 – next