microcontroller

1. Chapter (4):
Bios and Dos programming in
assembly
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Chapter (4):
Outlines:
 Bios INT 10H programming: using INT 10H to:
 Clear the screen
 Set the cursor position
 others
 Dos interrupt IN 21H: using INT 21H to:
 Input character from keyboard
 Output the character to screen
 Input & output string

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 Clearing the screen using INT 10H & function 06H:

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 Setting the cursor to specific location using INT 10H & function 02H:
 Get current cursor position using INT 10H & function 03H:

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 Outputting a string of data to the monitor using INT 21H & option 09:
 Outputting a single character to the monitor using INT 21H & option 02:
 Inputting a single character using INT 21H & option 01:
 Inputting a string of data from keyboard using INT 21H & option 0A:

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 Example:
TITLE FIRST: input letter from keyboard then print letter in new raw
.MODEL SMALL
.STACK 100H
.CODE
MAIN PROC
;display the character ‘?’
MOV AH,2
MOV DL,'?'
INT 21H
;read letter from keyboard
MOV AH,01
INT 21H
MOV BL,AL ; storage letter
MOV AH,02 ; display letter
MOV DL,0DH ; carriage return
INT 21H
MOV DL,0AH ; line feed
INT 21H
; display the input letter
MOV DL,BL
INT 21H
MOV AH,4CH
INT 21H
MAIN ENDP
END MAIN

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 Example:
TITLE THIRD: CASE CONVERSION PROGRAM (from small to capital)
.MODEL SMALL
.STACK 100H
.DATA
CR EQU 0DH
LF EQU 0AH
MSG1 DB 'ENTER A LOWER CASE LETTER: $'
MSG2 DB CR,LF,'IN UPPER CASE IT IS:'
CHAR DB ?,'$'
.CODE
MAIN PROC
; initialize DS
MOV AX,@DATA
MOV DS,AX
;print user prompt
LEA DX,MSG1
MOV AH,09H
INT 21H
;input character and convert to lower case
MOV AH,01H
INT 21H
SUB AL,20H
MOV CHAR,AL
;display on the next line
LEA DX,MSG2
MOV AH,09H
INT 21H
;return to DOS
MOV AH,4CH
INT 21H
MAIN ENDP
END MAIN
MOV DX,offset MSG1
To convert from small to capital

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 Example:
In text file

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 Example:
LEA DX,MESSAGE

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 Example:

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 Example:

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 Example:

13. Chapter (5):
Macro and the Mouse
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Chapter (5):
Outlines:
 Define macro and how to use in assembly:
 How macro expanding by assembler:
 How to control the expanded of macro in list file:
 Define the local variable in macro:
 How to include the macro in another file:

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 Macro allow the programmer to write the task (set of codes perform a specific job)
once only and to invoke it whenever it is needed wherever it is needed.
 In list file the code (string message1) is expanded to:

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 Can the macro contain comments?
 The answer is yes, but there is away to suppress comments and
make the assembler show only the code only.
 If comments are preceded by (;), they will show up in the list file.
 If comments are preceded by (;;), they will not show up in the list file.
 Or using 3 directives:
 .LALL (list all): list all the instructions and the comments that are preceding
by (;) and can not list the instructions and the comments that are preceding
by (;;)
 .SALL (suppress all)
 .XALL (executable all): list only the instructions

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 Example:

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 LOCAL directive: used to define label in macro.
MULTIPLY 2,4,RESULT

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 LOCAL directive: used to define label in macro.

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 INCLUDE directive: allows a programmer to write macros and save
them in a file (for ex. “MYMACRO1.MAC”), and later bring them
into any file or program.
Include macro to clear
screen, set cursor and
display string

21. Chapter (6):
Signed Numbers & Strings &
Tables
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Lifted……

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Chapter (6):
Outlines:
 Code string instructions:
 Explain the function of registers SI & DI in string
operation
 Explain the direction flag in string instructions
 (MOVSB, MOVSW, STOS, LODS, CMPS, SCAS)
 Tables processing:
 XLAT

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 Use of SI and DI, DS and ES in string instructions:
 In 8086, the SI and DI registers always point to the source and
destination operands, respectively.
 To generate the physical address, always uses SI as the offset
of the DS register and DI as the offset of ES register.
 By using the string instructions, they are capable of compare or
transfer or … two arrays of data located in memory locations
pointed at by the SI and DI registers.

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 Byte and Word operand in string instructions:

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 Direction flag (DF) in string instructions:
 Usually, We need the pointer (incremented or decremented) to
process operands located in memory locations.
 In string operations this is achieved by the direction flag (DF).
 DF is the bit 11 (D10) in the flag register (D0 – D15).
 DF is set to high or low in order to the choice of increment or
decrement the SI and DI pointers.
 By Using the instructions:
1) CLD (clear the DF): then DF = 0, indicate the pointers should
be increment automatically (autoincrement).
2) STD (set the DF): then DF = 1, indicate the pointers should be
decrement automatically.

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 Prefix:
 REP (repeat) prefix: allow a string instruction to repeat the
operation. (process is repeated until CX = 0).
 Using the REP with string instructions MOVS, STOS, and LODS.
 REPZ (repeat zero): is the same REPE (repeat equal), will repeat
the string operation as long as the source and destination are
equal (ZF =1) or until CX = 0.
 REPNZ (repeat not zero): is the same REPNE (repeat not equal),
will repeat the string operation as long as the source and
destination are not equal (ZF =0) or until CX = 0.
 Using the REPZ & REPNZ with string instructions CMPS and
SCANS.

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 Example: (MOVSB & MOVSW)

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 STOS & LODS instructions:
 STOSB instruction: stores the byte in AL register into
memory locations pointed at by ES:DI and increment DI
once if (DF = 0), if DF = 1, then DI is decremented once.
 STOSW instruction: stores the contents of AX register into
memory locations pointed at by ES:DI and ES:DI+1 (AL into
ES:DI and AH into ES:DI+1), then increment DI twice if (DF =
0), if DF = 1, then DI is decremented twice.
 LODSB instruction: loads the content of memory locations
pointed at by DS:SI into AL and increment SI once or
decrement SI once.
 LODSW instruction: : loads the content of memory
locations pointed at by DS:SI into AL and DS:SI+1 into AH
and increment SI twice or decrement SI twice.

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 Example: (STOS & LODS )

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 CMPS & SCANS instructions:
 CMPS (compare string) instruction: allows the comparison
of two arrays of data pointed at by the SI and DI registers.
And depending on which prefix REPE or REPNE is used, a
decision is made for equality or inequality.
 SCANS (scan string) instruction: compares each byte or
word of the array of data pointed at by ES:DI with the
contents of the AL or AX. And depending on which prefix
REPE or REPNE is used, a decision is made for equality or
inequality.

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 Example: (CMPS )

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 Example: (SCANS)

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 XLAT instructions & Look-up tables:
 In some computer application, we need a table that holds
some important information or some values.
 To access the elements in the table using the XLAT
(translate) instruction.
 The table is commonly referred to a look-up table.
 To access the square value for number 5:

34. Any Question?
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