STC89C53RC datasheet(157/165 Pages) STC

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Data types used in 8051 C language

Data Type

Bits

Bytes Value Range

bit

0 to 1

signed char

-128 to +127

unsigned char

0 to 255

enum

-32768 to +32767

signed short

-32768 to +32767

unsigned short

0 to 65535

signed int

-32768 to +32767

unsigned int

0 to 65535

signed long

-2,147,483,648 to +2,147,483,647

unsigned long

0 to 4,294,967,295

float

±1.175494E-38 to ±3.402823E+38

sbit

0 to 1

sfr

0 to 255

sfr16

0 to 65535

The data type sbit is somewhat similar to the bit data type, except that it is normally used to declare 1-bit

variables that reside in special function registes (SFRs). For example:

sbit

P = 0xD0;

declares the sbit variable P and specifies that it refers to bit address D0H, which is really the LSB of the PSW

SFR. Notice the difference here in the usage of the assignment ("=") operator. In the context of sbit declarations,

it indicatess what address the sbit variable resides in, while in bit declarations, it is used to specify the initial

value of the bit variable.

Besides directly assigning a bit address to an sbit variable, we could also use a previously defined sfr

variable as the base address and assign our sbit variable to refer to a certain bit within that sfr. For example:

sfr

PSW = 0xD0;

sbit

P = PSW^0;

This declares an sfr variable called PSW that refers to the byte address D0H and then uses it as the base address

to refer to its LSB (bit 0). This is then assigned to an sbit variable, P. For this purpose, the carat symbol (^) is used

to specify bit position 0 of the PSW.

A third alternative uses a constant byte address as the base address within which a certain bit is referred. As

an illustration, the previous two statements can be replaced with the following:

sbit

P = 0xD0 ^ 0;

Meanwhile, the sfr data type is used to declare byte (8-bit) variables that are associated with SFRs. The

statement:

sfr

IE = 0xA8;

declares an sfr variable IE that resides at byte address A8H. Recall that this address is where the Interrupt Enable

(IE) SFR is located; therefore, the sfr data type is just a means to enable us to assign names for SFRs so that it is

easier to remember.

The sfr16 data type is very similar to sfr but, while the sfr data type is used for 8-bit SFRs, sfr16 is used for

16-bit SFRs. For example, the following statement:

sfr16

DPTR = 0x82;

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