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Technical Support
On-Line Manuals
Cx51 User's Guide
Cx51 Introduction
Compiling Programs
Language Extensions
Keywords
Memory Areas
Program Memory
Internal Data Memory
External Data Memory
Far Memory
SFR Memory
Memory Models
Small Model
Compact Model
Large Model
Memory Types
bdata
code
data
far
idata
pdata
xdata
Data Types
Special Function Registers
sfr
sfr16
sbit
Bit-Addressable Objects
bit
Standard C Types
void
char
int
enum
float
double
Type Modifiers
signed
unsigned
short
long
Type Qualifiers
const
volatile
Storage Classes
auto
register
extern
static
Absolute Variable Location
Pointers
Generic Pointers
Memory-Specific Pointers
Pointer Conversions
Abstract Pointers
Function Declarations
Parameters and the Stack
Parameters and Registers
Return Values
Memory Models
Register Banks
Register Bank Access
Interrupt Functions
Reentrant Functions
Alien (PL/M-51) Function
Real-Time Function Tasks
Preprocessor
Advanced Programming
8051 Derivatives
Error Messages
Library Reference
Appendix
Large Model
In the large model, all variables, by default, reside in external data memory (which may be up to 64K Bytes). This is the same as if they were explicitly declared using the xdata memory type specifier.
The data pointer (DPTR) is used to address external memory. It is important to note that memory access through the data pointer is inefficient and slow, especially on variables that are two or more bytes long. This type of data access mechanism generates more code than the small model or compact model.
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