Control Statements

The A251 Assembler provides a number of control statements that permit you to define symbol values, reserve and initialize storage, and control the placement of your code.

These statements should not be confused with processor instructions or with assembler directives. They do not produce executable code and, with the exception of the DB, DD, and DW statements, they have no direct effect on the contents of code memory. These controls change the state of the assembler, define user symbols, and add information to the object file.

Control statements may be divided into the following categories:

Address Control

Statement	Description
EVEN	Forces the location counter to the next even address.
ORG	Sets the location counter to a specifies offset or address.
USING	Specifies which register bank to use.

Memory Initialization

Statement	Description
DB	Allocates memory for one or more defined byte values.
DD	Allocates memory for one or more defined double word values.
DW	Allocates memory for one or more defined word values.

Memory Reservation

Statement	Description
DBIT	Reserves space for one or more bits.
DS	Reserves space for one or more bytes.
DSB	Reserves space for one or more bytes.
DSD	Reserves space for one or more double words.
DSW	Reserves space for one or more words.

Procedure Declaration

Statement	Description
ENDP	Defines the end of a function.
LABEL	Assigns an address to a symbolic name.
PROC	Defines the beginning of a function.

Program Linkage

Statement	Description
EXTERN	Defines external symbols.
EXTRN	Defines external symbols.
NAME	Specifies the name of the current module.
PUBLIC	Defines symbols which may be used in other modules.

Segment Control

Statement	Description
BSEG	Defines an absolute bit segment.
CSEG	Defines an absolute code segment.
DSEG	Defines an absolute data segment.
ISEG	Defines an absolute idata segment.
RSEG	Selects a relocatable segment.
SEGMENT	Defines a relocatable segment.
XSEG	Defines an absolute xdata segment.

Symbol Definition

Statement	Description
BIT	Defines an address in bit space.
CODE	Defines an address in code space.
DATA	Defines an address in data space.
EQU	Sets a permanent symbol value.
IDATA	Defines an address in idata space.
LIT	Assigns a text string to a symbol name.
SBIT	Defines a bit SFR.
SET	Sets or resets a symbol value.
SFR	Defines a byte SFR.
SFR16	Defines a word SFR.
XDATA	Defines an address in xdata space.

Miscellaneous

Statement	Description
__ERROR__	Generates an error message.
END	Signals the end of the assembly module.