STC89C53RC datasheet(160/165 Pages) STC

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A program is explicitly selected to be in a certain memory model by using the C directive, #pragma. Otherwise,

the default memory model is small. It is recommended that programs use the small memory model as it allows for

the fastest possible access by defaulting all variables to reside in internal data memory.

The compact memory model causes all variables to default to the first page of external data memory while

the large memory model causes all variables to default to the full external data memory range of up to 64 Kbytes.

ARRAYS

Often, a group of variables used to store data of the same type need to be grouped together for better readability.

For example, the ASCII table for decimal digits would be as shown below.

ASCII table for decimal digits

Decimal Digit

ASCII Code In Hex

30H

31H

32H

33H

34H

35H

36H

37H

38H

39H

To store such a table in an 8051 C program, an array could be used. An array is a group of variables of the same

data type, all of which could be accessed by using the name of the arrary along with an appropriate index.

The array to store the decimal ASCII table is:

int

table [10] =

{0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39};

Notice that all the elements of an array are separated by commas. To access an individul element, an index

starting from 0 is used. For instance, table[0] refers to the first element while table[9] refers to the last element in

this ASCII table.

STRUCTURES

Sometime it is also desired that variables of different data types but which are related to each other in some way

be grouped together. For example, the name, age, and date of birth of a person would be stored in different types

of variables, but all refer to the person's personal details. In such a case, a structure can be declared. A structure is

a group of related variables that could be of different data types. Such a structure is declared by:

struct

person {

char name;

int age;

long DOB;

};

Once such a structure has been declared, it can be used like a data type specifier to create structure variables that

have the member's name, age, and DOB. For example:

struct

person

grace = {"Grace", 22, 01311980};

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