PicC 9.50 dsPIC Manual.pdf

Macro AssemblerHI-TECH C Assembly LanguageHere, the label frank will ultimately be assigned the address of the mov instruction, and simon44 theaddress of the clrf instruction. Regardless of how they are defined, the assembler list file producedby the assembler will always show labels on a line by themselves.Labels may be used (and are prefered) in assembly code rather than using an absolute address.Thus they can be used as the target location for jump-type instructions or to load an address into aregister.Like variables, labels have scope. By default, they may be used anywhere in the module in whichthey are defined. They may be used by code above their definition. To make a label accessable inother modules, use the GLOBAL directive. See Section 4.3.8.1 for more information.4.3.6 ExpressionsThe operands to instructions and directives are comprised of expressions. Expressions can be madeup of numbers, identifiers, strings and operators.Operators can be unary (one operand, e.g. not) or binary (two operands, e.g. +). The operatorsallowable in expressions are listed in Table 4.4. The usual rules governing the syntax of expressionsapply.The operators listed may all be freely combined in both constant and relocatable expressions. TheHI-TECH linker permits relocation of complex expressions, so the results of expressions involvingrelocatable identifiers may not be resolved until link time.4.3.7 Program SectionsProgram sections, or psects, are simply a section of code or data. They are a way of grouping togetherparts of a program (via the psect’s name) even though the source code may not be physically adjacentin the source file, or even where spread over several source files.•The concept of a program section is not a HI-TECH-only feature. Often referred to asblocks or segments in other compilers, these grouping of code and data have long usedthe names text, bss and data.A psect is identified by a name and has several attributes. The PSECT assembler directive is usedto define a psect. It takes as arguments a name and an optional comma-separated list of flags. SeeSection 4.3.8.3 for full information on psect definitions. Chapter 5 has more information on theoperation of the linker and on optins that can be used to control psect placement in memory.The assembler associates no significance to the name of a psect and the linker is also not awareof which are compiler-generated or user-defined psects. Unless defined as abs (absolute), psects arerelocatable.73