Page 166 - Programming Microcontrollers in C

Small 8-Bit Systems 151

A pragma is a C preprocessor command not defined by the lan­
guage. As such, the compiler writer can use the #pragma command
to satisfy a need not specifically identified by the language. C6805
uses pragmas to identify microcontroller-specific characteristics.
Table 4-2 contains a list of pragmas used by C6805. The format of a
pragma directive here is
#pragma portxx portname @ address

where portxx can be portr, portw, or portrw which shows
whether the port is read, write, or both. portname is the name used
in the program for the port. The at symbol (@) identifies a memory
address. #pragma mor identifies the contents of the masked option
register used on field programmable chips. There are some instruc­
tions that are not found across the whole M68HC05 family. In
particular, some devices may not have the MUL, the DIV, the STOP,
and the WAIT instruction. The #pragma has a preprocessor call
that identifies the instructions from this set in the particular
microcontroller.

pragma Function
#pragma portxy
I/O port definition
#pragma memory
RAM/ROM definition
#pragma mor
mask option register
#pragma has
instruction set options
#pragma options
compiler directives
#pragma vector
interrupt vector definitions
Table 4-2: C6805 pragma Directives
This compiler has certain options that can be inserted from the
command line or, if needed by the programmer, the #pragma op­
tions preprocessor command can also be used to set the appropriate
compiler options. Finally, the #pragma vector identifies a given
function name as an interrupt service routine. When the compiler com­
piles the name specified, it will place the address of the function into
the defined vector location. Another modification in the compiled code
will take place when #pragma vector is used. All returns from a
function identified by a vector pragma will use the return from in­
terrupt instruction rather than the usual return from subroutine.