chapter7.2-mikroprocessor

Programming the Microprocessor

A Course in Microprocessor

Electrical Engineering Dept.

University of Indonesia

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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

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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)

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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

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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

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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

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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

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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

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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

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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

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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)

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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

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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)

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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)

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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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