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  • 1. Programming the Microprocessor A Course in Microprocessor Electrical Engineering Dept. University of Indonesia
  • 2. Data Conversions
      • Describes conversions between binary and ASCII
      • Binary data are removed from a register or memory and converted to ASCII for the video display
  • 3.
    • Converting from Binary to ASCII
      • Conversion from binary to ASCII is accomplished in two ways :
        • by the AAM instruction if the number is less than 100 or
        • by a series of decimal divisions (divided by 10)
    Data Conversions (cont’d)
  • 4. Data Conversions (cont’d)
      • The algorithm for converting from binary to ASCII code is :
        • Divide by the 10 and save the remainder on the stack as a significant BCD Digit
        • Repeat step 1 until the quotient is a 0
        • Retrieve each remainder and add a 30H to convert to ASCII before displaying or printing
      • Example 7-27 illustrates a program that uses the procedure DISP that processes the binary value in AL (0-99) and display it on the video screen as decimal
  • 5. Data Conversions (cont’d)
    • Converting from ASCII to Binary
      • The algorithm for converting from ASCII to binary is :
        • Begin with a binary result of 0
        • Subtract 30H from the character typed on the keyboard to convert it to BCD
        • Multiply the result by 10 and add the new BCD digit
        • Repeat steps 2 and 3 until the character typed is not an ASCII-coded number
      • Example 7-29 illustrates a procedure (READN) used in a program that implements this algorithm
  • 6. Data Conversions (cont’d)
    • Displaying and Reading Hexadecimal Data
      • Reading Hexadecimal Data
        • see Example 7-30
      • Displaying Hexadecimal Data
        • see Example 7-31
    • Using Lookup Tables for Data Conversions
      • A lookup table is formed in the memory as a list of data that is referenced by a procedure to perform conversions
      • is used XLAT instruction
  • 7. Data Conversions (cont’d)
      • Converting from BCD to 7-segment Code
        • Example 7-32 illustrates a lookup table that contains the 7-segment codes for the numbers 0 to 9
      • Using a Lookup Table to Access ASCII Data
        • Example 7-33 shows a table that references ASCII-coded character strings located in the code segment
  • 8. Disk Files
      • Data are found stored on the disk in the form of files
      • The disk is organized in four main parts :
        • the boot sector
        • the file allocation table (FAT)
        • the root directory
        • the data storage
    • Disk Organization
      • Fig. 7-2 illustrates the organization of sectors and tracks on the surface of the disk
      • Fig. 7-3 shows the organization of data on a disk
  • 9. Disk Files (cont’d)
      • Files are usually accessed through DOS INT 21H function calls
        • There are two ways to accesse a file using
        • INT 21H :
          • uses a file control block
          • uses a file handle
    • Sequential File Access
      • All DOS files are sequential files
  • 10. Disk Files(cont’d)
      • File Creation
        • A file is created by the INT 21 H function call number 3CH
        • The file name must be stored at a location addressed by DS:DX before calling the function
        • CX must contain the attribute of the file (or subdirectory) created
        • An ASCII-Z string is a character string that ends with a 00H or null character
        • Example 7-37 lists a short procedure that creates the new file on the disk
        • Table 7-5 lists and defines the attribute bit positions
  • 11. Disk Files(cont’d)
      • Writing to a File
        • Before writing to a file, the file must have been created or opened
        • The file handle is used to refer to the file whenever data are written
        • Function number 40H is used to write data to an opened or newly created file. In addition to loading a 40H into AH, we must also load BX = the file handle, CX = the number of bytes to be written, and DS:DX = the address of the area to be written to the disk ( see Example 7-38 and 7-39 )
  • 12. Disk Files(cont’d)
      • The File Pointer
        • It is a 32-bit number that addresses any byte in a file
        • Once a file is opened, the file pointer can be changed with the move file pointer function number 42H
        • A file pointer can be moved :
          • from the start of the file (AL=00H)
          • from the current location (AL=01H)
          • from the end of the file (AL=02H)
        • The distance moved by the file pointer is specified by registers CX and DX
  • 13. Disk Files(cont’d)
        • Register BX must contain the file handle before using function 42H to move the file pointer
        • Example 7-40 shows a procedure that opens a file, moves the file pointer to the end of the file, writes 256 bytes of data, and then closes the file
        • Fig. 7-5 shows how this is accomplished by creating a second file (see Example 7-41 )
      • Random Access Files
        • Creating a Random Access File (see Example 7-42 )
        • Reading and Writing a Record (see Example 7-43 )
  • 14. Example Programs
    • Calculator Program
      • This program demonstrates how data conversion plays an important part in many application programs (see Example 7-44 )
    • Numeric Sort Program
      • Fig. 7-6 shows five numbers that are sorted with a bubble sort
      • Example 7-45 illustrates a program that accepts 10 numbers from the keyboard (0-65535)
  • 15. Interrupt Hooks
      • Hooks are used to tap into or intercept the interrupt structure of the microprocessor
      • a special keystroke, called a hot key, can be detected when we hook into the keyboard interrupt
      • Whenever the hot-key is typed, a terminate and stay resident (TSR) program that performs a special task, can be accessed
      • see Example 7-48
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