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Microcontroller Cross Compiler

Compiler is a program that transforms higher language source code(such as c code) to the lower language code(assembly language/machine code/binary code/object code). This object code can be ported on any target such as microcontroller/processor. The reason for this conversion is to create an executable program for the desired target.

When the target compiled program runs on a computer/platform/system in which CPU/operating system is different from where compiler is installed,this compiler is referred as cross-compiler.

Tools such as µVision are widely used as compiler for different microcontroller variants. The µVision helps create and test embedded applications for ARM/Cortex-M C166/C251/C51 microcontrollers.

Following memory type models,variable types,SFRs are used in 8051 based cross compiler.

Memory types

The memory model specifies which default memory type to use for following:
• function arguments
• automatic variables
• declarations with no explicit memory type specifier.
• One can specify the memory model on the Cx51 command line using SMALL, COMPACT and LARGE directives.

Memory type specifier

Memory Type Description
code Program memory
data Directly addressable internal data memory
idata Indirectly addressable internal data memory
bdata bit addressable internal data memory
xdata External data memory
pdata Paged external data memory

Variable data type specifier

Variable data type Bits Bytes Value Range
bit 1 0 to 1
Signed char 8 1 -128 to +127
unsigned char 8 1 0 to 255
signed short 16 2 -32768 to +32767
unsigned short 16 2 0 to 65535
signed int 16 2 -32768 to +32767
unsigned long 32 4 0 to 4294967295
float 32 4 +/- 1.17E-38 to +/-3.40E+38
sbit 1 0 to 1
sfr 8 1 0 to 255

Special Function Registers(SFRs)

Intel 8051 family microprocessors specify distinct memory area for accessing SFRs. SFRs are used mainly to control timers/counters/serial I/Os and port I/Os, peripherals. SFRs are addressed from 0x80 to 0xFF and they can be accessed as bits, bytes, and words. SFRs are declared in the same fashion as other C variable types.

sfr P0 = 0x80; /* Port-0, address 80h */

Generic pointers/Memory-specific Pointers

Generic pointers are declared in the same fashion as standard C pointers.

int *numptr; /* int ptr */

specify the memory area in which a generic pointer is stored by using a memory type specifier.

int xdata *numtab; /* ptr to int(s) in xdata */

Download Evaluation development tools for all 8051 and 80251 devices from KEIL.



• Microcontroller tutorial
• What is microcontroller
• 8051 Microcontroller Architecture
• Microcontroller hardware Interfacing


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