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4.2: DOS INTERRUPT 21H Option 0AH inputting a data string from the keyboard

4.2: DOS INTERRUPT 21H Option 0AH inputting a data string from the keyboard. A means by which one can get keyboard data from & store it in a predefined data segment memory area. Register AH = 0AH. DX = offset address at which the string of data is stored.

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4.2: DOS INTERRUPT 21H Option 0AH inputting a data string from the keyboard

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  1. 4.2: DOS INTERRUPT 21H Option 0AHinputting a data string from the keyboard • A means by which one can get keyboard data from & store it in a predefined data segment memory area. • Register AH = 0AH. • DX = offset address at which the string of data is stored. • Commonly referred to as a buffer area. • DOS requires a buffer area be defined in the data segment. • The first byte specifies the size of the buffer. • The number of characters from the keyboard is in the second byte. • Keyed-in data placed in the buffer starts at the third byte.

  2. 4.2: DOS INTERRUPT 21H Option 0AHinputting a data string from the keyboard • This program accepts up to six characters from the keyboard, including the return (carriage return) key. • Six buffer locations were reserved, and filled with FFH. • Memory contents of offset 0010H: • The PC won’t exit INT 21H until it encounters a RETURN.

  3. 4.2: DOS INTERRUPT 21H Option 0AHinputting a data string from the keyboard • Assuming the data entered through the keyboard was "USA" <RETURN>, the contents of memory locations starting at offset 0010H would look like: • 0010H = 06 DOS requires the size of the buffer here. • 0011H = 03 The keyboard was activated three times (excluding the RETURN key) to key in letters U, S, and A. • 0012H = 55H ASCII hex value for letter U. • 0013H = 53H ASCII hex value for letter S. • 0014H = 41H ASCII hex value for letter A. • 0015H = 0DH ASCII hex value for CR. (carriage return)

  4. 4.2: DOS INTERRUPT 21H inputting more than buffer size • Entering more than six characters (five + the CR = 6) will cause the computer to sound the speaker. • The contents of the buffer will look like this: • Location 0015 has ASCII 20H for <SPACE> • Location 0016 has ASCII 61H for "a“. • Location 0017 has 0D for <RETURN> key. • The actual length is 05 at memory offset 0011H.

  5. CR is not included in the count. 4.2: DOS INTERRUPT 21H inputting more than buffer size • If only the CR key is activated & no other character: • 0AH is placed in memory 0020H. • 0021H is for the count. • 0022H IS the first location to have data that was entered. • If only the <RETURN> key is activated, 0022H has 0DH, the hex code for CR. • The actual number of characters entered is 0 at location 0021.

  6. 4.2: DOS INTERRUPT 21H use of carriage return and line feed • In Program 4-2, the EQU statement is used to equate CR (carriage return) with its ASCII value of 0DH, and LF (line feed) with its ASCII value of 0AH. • See pages 141 & 142 • Program 4-3 prompts the user to type in a name with a maximum of eight letters. • The program gets the length and prints it to the screen. • See page 143. • Program 4-4 demonstrates many functions described in this chapter. • See pages 144 & 145.

  7. 4.2: DOS INTERRUPT 21H Option 07keyboard input without echo • Option 07 requires the user to enter a single character, which is not displayed (or echoed)on the screen. • The PC waits until a single character is enteredand provides the character in AL.

  8. 4.2: DOS INTERRUPT 21H using LABEL to define a string buffer • The LABEL directive can be used in the data segment to assign multiple names to data. • Used to assign the same offset address to two names. • The attribute can be: • BYTE; WORD; DWORD; FWORD; QWORD; TBYTE. • In the following: • The offset address assigned to JOE is the same offset address for TOM since the LABEL directive does not occupy any memory space.

  9. 4.2: DOS INTERRUPT 21H using LABEL to define a string buffer • Use this directive to define a buffer area for thestring keyboard input: • In the code segment the data can be accessed by name as follows:

  10. 4.3: WHAT IS A MACRO, AND HOW IS IT USED? • There are applications in Assembly language programming where a group of instructions performs a task used repeatedly. • It does not make sense to rewrite them every time. • Macros allow the programmer to write the task once only & invoke it whenever, wherever it is needed. • Reduces time to write code & reduce possibility of errors.

  11. 4.3: WHAT IS A MACRO, AND HOW IS IT USED?MACRO definition • Every macro definition must have three parts: • The MACRO directive indicates the beginning of the macro definition, ENDM directive signals the end. • In between is the body of the macro. • The name must be unique and must follow Assembly language naming conventions. • Dummies are names, parameters, or registersthat are mentioned in the body of the macro. • The macro can be invoked (or called) by its name, and appropriate values substituted for dummy parameters.

  12. 4.3: WHAT IS A MACRO, AND HOW IS IT USED?MACRO definition • A macro for displaying a string of data using the widely used function 09 of INT 21H:

  13. 4.3: WHAT IS A MACRO, AND HOW IS IT USED?MACRO definition • In the following code segment, the macro can beinvoked by its name with the user's actual data: • Instruction "STRING MESSAGE1" invokes the macro. • The assembler expands the macro by providing the following code in the .LST file: • The (1) indicates that the code is from the macro. • Earlier versions of MASM, used a plus sign (+).

  14. 4.3: WHAT IS A MACRO, AND HOW IS IT USED?comments in a macro • Two types of comments in the macro: • Listable; Nonlistable. • Comments preceded by one semicolon (;) will show up in the ".lst" file when the program is assembled. • Those preceded by a double semicolon (;;) will not.

  15. 4.3: WHAT IS A MACRO, AND HOW IS IT USED?comments in a macro • Three directives designed to make programs that use macros more readable, affecting the ".lst" file, with no effect on the ".obj" or ".exe" files: • .LALL (List ALL) will list all instructions/comments preceded by a single semicolon in the ".lst" file. • .SALL (Suppress ALL) suppresses the listing of the macro body and the comments. • Used to make the list file shorter and easier to read • Will not eliminate any opcode from the object file. • .XALL (eXecutable ALL) is used to list only the part of the macro that generates opcodes. • The default listing directive.

  16. 4.3: WHAT IS A MACRO, AND HOW IS IT USED?LOCAL directive and its use in macros • If a macro is expanded more than once, and there is a label in the label field of the body of the macro, these labels must be declared as LOCAL. • Otherwise, an assembler error would be generated when the same label was encountered in two or more places. • Rules which must be observed in the macro body: • 1. All labels in the label field must be declared LOCAL. • 2. LOCAL directive must be right after the MACRO directive. • 3. The LOCAL directive can be used to declare all names and labels at once.

  17. 4.3: WHAT IS A MACRO, AND HOW IS IT USED?LOCAL directive and its use in macros • In example 4-7, the "BACK" label is defined as LOCAL right after the MACRO directive.

  18. 4.3: WHAT IS A MACRO, AND HOW IS IT USED?INCLUDE directive • The INCLUDE directive allows a programmer to write macros, save them in a file, and later bring them into any file. • Used to bring this file into any ".asm" file, to allowthe program can call any of the macros as needed. • See Program 4 -7 on pages 155-157. • In the list file of Program 4-7, the letter "C" in frontof the lines indicates that they are copied from another file and included in the present file.

  19. Dec Hex Bin 4 4 00000100 ENDS ; FOUR

  20. Dec Hex Bin 5 5 00000101 ORG ; FIVE Keyboardand Mouse Programming

  21. 5.1: INT 16H KEYBOARD PROGRAMMING • The original IBM PC keyboard had 83 keys, in three major groupings: • 1. The standard typewriter keys. • 2. Ten function keys, F1 to F10. • 3. 15-key keypad. • In later years, 101 key enhanced keyboards have become popular.

  22. See the scan code tables on pages 162 - 163 of your textbook. 5.1: INT 16H KEYBOARD PROGRAMMINGkeyboard scan codes • Each key is associated with a scan code.

  23. When a key is pressed, the OS stores its scan code in memory locations called a keyboard buffer, located inthe BIOS data area. 5.1: INT 16H KEYBOARD PROGRAMMING • The same scan code is used for a given lowercase letter and its capital, and all keys with dual labels. • The keyboard shift status byte distinguishes the keys. • Some INT 16H function calls provide the status byte in AL. • For keyboard-motherboard, interaction IBM has provided INT 16H.

  24. 5.1: INT 16H KEYBOARD PROGRAMMING checking a key press • For a program to run tasks continuously while checking for a keypress requires use of INT 16H. • A BIOS interrupt used exclusively for the keyboard. • To check a keypress, use INT 16H function AH = 01. • If ZF = 0, there is a key press. • If ZF = 1, there is no key press. • This function does not wait for the user to press a key—it simply checks to see if there is a key press. • If a character is available, it returns the scan codein AH, and the ASCII code in AL.

  25. To stop the bell sound, the user must press any key. 5.1: INT 16H KEYBOARD PROGRAMMING checking a key press • Program 5-1 sends the ASCII bell character, 07 hex to the screen continuously.

  26. 5.1: INT 16H KEYBOARD PROGRAMMINGwhich key is pressed? • INT 16H AH = 0 determines the key pressed. • This function must be used immediately after AH = 01. • AH = 0 doesn’t return until a key is pressed. • AH = 1 comes back whether or not a key has been pressed. • AL contains the ASCII character of the pressed key. • The scan key is in AH. • For characters such as F1–F10 for which there is no ASCII code, the scan code is in AH and AL = 0. • Thus, if AL = 0, a special function key was pressed.

  27. To stop the bell sound, the user must press a specific key. Test for the correct keypress to stop the bell 5.1: INT 16H KEYBOARD PROGRAMMINGwhich key is pressed?

  28. 5.1: INT 16H KEYBOARD PROGRAMMINGother INT 16H functions • INT 16H, AH = 10H(read a character) - the same as AH = 0, exceptthat it also accepts the additional keys on the IBM extended (enhanced) keyboard. • INT 16H, AH = 11H(find if a character is available) - the same asAH = 1, except that it also accepts the additionalkeys on the IBM extended (enhanced) keyboard.

  29. 5.2: MOUSE PROGRAMMING WITH INT 33H detecting the presence of a mouse • Because the original IBM PC & DOS did not provide support for the mouse, interrupt INT 33H is not part of BIOS or DOS. • INT 33H is part of the mouse driver software installedwhen the PC is booted. • The first task of any INT 33H program should be to verify the presence of a mouse and the number of buttons it supports, using INT 33H function AX = 0. • On return from INT 33H, if AX = 0, no mouse is supported. • If AX = FFFFH, the mouse is supported and the numberof mouse buttons will be contained in register BX.

  30. Do not forget the"H“, indicating hex. If absent, the compilerassumes it is decimal& executes INT 21H. (33 decimal = 21H) 5.2: MOUSE PROGRAMMING WITH INT 33H detecting the presence of a mouse • Although most mice have two buttons, right and left, there are some with middle buttons as well. • In INT 21H & INT 10H, register AH is used to select functions —not the case in INT 33H. • AL is used to select various functions and AH is set to 0. • The reason for "MOV AX,0".

  31. 5.2: MOUSE PROGRAMMING WITH INT 33H some mouse terminology • The mouse pointer (or cursor) is the pointer on the screen indicating where the mouse is pointing at a given time. • In graphics mode it is an arrow. • In text mode, a flashing block. • As the mouse is moved, the mouse cursor is moved.

  32. 5.2: MOUSE PROGRAMMING WITH INT 33H some mouse terminology • While movement of the mouse is measured in inches (or centimeters), movement of the mouse cursor on the screen is measured in units called mickeys. • Mickey units indicate mouse sensitivity. • A mouse that can move the cursor 200 units forevery inch of mouse movement has a sensitivityof 200 mickeys. • In this case, one mickey represents 1/200 of an inchon the screen. • Some mice have a sensitivity of 400 mickeys in contrastto the commonly used 200 mickeys.

  33. 5.2: MOUSE PROGRAMMING WITH INT 33H displaying and hiding the mouse cursor • The AX = 01 function of INT 33H is used to display the mouse cursor. • If the video mode is graphics, the mouse arrow is visible. • If the video mode is text, a rectangular block representing the mouse cursor becomes visible. • The color of the mouse cursor block is the opposite ofthe background color in order to be visible. • To hide the mouse cursor after making it visible, execute option AX = 02 of INT 33H.

  34. 5.2: MOUSE PROGRAMMING WITH INT 33H video resolution vs. mouse resolution • When the video mode is set to text mode, the mouse will automatically adopt the same resolution of 640 × 200 for its horizontal/vertical coordinates. • When a program gets the mouse cursor position, values are provided in pixels and must be divided by 8. • To get position in terms of character locations 0 to 79 (horizontal) and 0 to 24 (vertical) on the screen.

  35. The mouse also adopts these graphics resolutions. 5.2: MOUSE PROGRAMMING WITH INT 33H video resolution vs. mouse resolution • In graphics modes, resolution is 640 × 200, 640 × 350 and 640 × 480.

  36. 5.2: MOUSE PROGRAMMING WITH INT 33H getting the current mouse cursor position • Option AX = 03 of INT 33H gets the current position of the mouse cursor. • On return, the X & Y coordinates are in registersCX (horizontal) and DX (vertical). • BX contains the button status, 1 if down, 0 if up. • D0 = left button; D1 = right button; D2 = center button. • The cursor position is given in pixels. • To get the mouse cursor character position, dividethe horizontal and vertical values of CX & DX by 8. • See Programs 5-3 & 5-4 on pages 168 - 171of your textbook.

  37. 5.2: MOUSE PROGRAMMING WITH INT 33H setting the mouse pointer position • INT 33H option AX = 04 allows a program to setthe mouse pointer to a new location anywhereon the screen. • Coordinates for the new location must be placed inCX for the horizontal (x coordinate) and DX for thevertical (y coordinate). • Values must be in pixels. • In the range of 0–639 & 0–199 for 640 × 200 resolution. • Coordinate (0,0) is the upper left corner of the screen.

  38. Program 5-4 on pages 170 - 171 of your textbook shows one way to use this function. 5.2: MOUSE PROGRAMMING WITH INT 33H getting mouse button press information • INT 33H option AX = 05 is used to get information about specific button presses since the last call to this function.

  39. 5.2: MOUSE PROGRAMMING WITH INT 33H the button press count program • Program 5-5 on pages 172 - 173 uses the AX = 05 function to monitor the number of times the left button is pressed and then displays the count. • It prompts the user to press the left button a numberof times. • When the user is ready to see how many times the buttonwas pressed, any key can be pressed.

  40. Dec Hex Bin 5 5 00000101 ENDS ; FIVE

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