MPLAB C Compiler for PIC24 MCUs and dsPIC DSCs ... - Microchip

7.6 USING MACROS
Device Support Files
Processor header files define, in addition to special function registers, useful macros
for the 16-bit family of devices.
• Configuration Bits Setup Macros
• Inline Assembly Usage Macros
• Data Memory Allocation Macros
• ISR Declaration Macros
7.6.1 Configuration Bits Setup Macros
Macros are provided that can be used to set configuration bits. For example, to set the
FOSC bit using a macro, the following line of code can be inserted before the beginning
of your C source code:
_FOSC(CSW_FSCM_ON & EC_PLL16);
This would enable the external clock with the PLL set to 16x and enable clock switching
and fail-safe clock monitoring.
Similarly, to set the FBORPOR bit:
_FBORPOR(PBOR_ON & BORV_27 & PWRT_ON_64 & MCLR_DIS);
This would enable Brown-out Reset at 2.7 Volts and initialize the Power-up timer to 64
milliseconds and configure the use of the MCLR pin for I/O.
For a complete list of settings valid for each configuration bit, refer to the processor
header file.
7.6.2 Inline Assembly Usage Macros
Some Macros used to define assembly code in C are listed below:
#define Nop() {__asm__ volatile ("nop");}
#define ClrWdt() {__asm__ volatile ("clrwdt");}
#define Sleep() {__asm__ volatile ("pwrsav #0");}
#define Idle() {__asm__ volatile ("pwrsav #1");}
7.6.3 Data Memory Allocation Macros
Macros that may be used to allocate space in data memory are discussed below. There
are two types: those that require an argument and those that do not.
The following macros require an argument N that specifies alignment. N must be a
power of two, with a minimum value of 2.
#define _XBSS(N) __attribute__((space(xmemory), aligned(N)))
#define _XDATA(N) __attribute__((space(xmemory), aligned(N)))
#define _YBSS(N) __attribute__((space(ymemory), aligned(N)))
#define _YDATA(N) __attribute__((space(ymemory), aligned(N)))
#define _EEDATA(N) __attribute__((space(eedata), aligned(N)))
For example, to declare an uninitialized array in X memory that is aligned to a 32-byte
address:
int _XBSS(32) xbuf[16];
To declare an initialized array in data EEPROM without special alignment:
int _EEDATA(2) table1[] = {0, 1, 1, 2, 3, 5, 8, 13, 21};
The following macros do not require an argument. They can be used to locate a
variable in persistent data memory or in near data memory.
#define _PERSISTENT __attribute__((persistent))
#define _NEAR __attribute__((near))
© 2008 Microchip Technology Inc. DS51284H-page 95