HLASM Language Reference

Operand Entries
“Program Structures and Addressing” on page 50 describes how you use symbolic
addresses to refer to data in your assembler language program.
Defining Symbolic Addresses: Define relocatable addresses by either using a
symbol as the label in the name field of an assembler language statement, or
equating a symbol to a relocatable expression.
Define absolute addresses (or values) by equating a symbol to an absolute
expression.
Referring to Addresses: You can refer to relocatable and absolute addresses in
the operands of machine instruction statements. (Such address references are
also called addresses in this manual.) The two ways of coding addresses are:
Implicitly—in a form that the assembler must first convert into an explicit
relative-offset or base-displacement form before it can be assembled into object
code.
Explicitly—in a form that can be directly assembled into object code.
Implicit Address
An implicit address is specified by coding one expression. The expression can be
relocatable or absolute. The assembler converts all implicit addresses into their
relative-offset or base-displacement form before it assembles them into object code.
The assembler converts implicit addresses into explicit base-displacement
addresses only if a USING instruction has been specified, or for small absolute
expressions, where the address is resolved without a USING. The USING
instruction assigns both a base address, from which the assembler computes
displacements, and a base register, which is assumed to contain the base address.
The base register must be loaded with the correct base address at execution time.
For more information, refer to “Addressing” on page 63.
Explicit Address
An explicit address is specified by coding two absolute expressions as follows:
The first is an absolute expression for the displacement, whose value must lie
in the range 0 through 4095 (4095 is the maximum value that can be
represented by the 12 binary bits available for the displacement in the object
code).
The second (enclosed in parentheses) is an absolute expression for the base
register, whose value must lie in the range 0 through 15.
An explicit base register designation must not accompany an implicit address.
However, in RX-format instructions, an index register can be coded with an implicit
address as well as with an explicit address. When two addresses are required,
each address can be coded as an explicit address or as an implicit address.
Relative Address
A relative address is specified by coding one expression. The expression may be
relocatable or absolute. If a relocatable expression is used, then the assembler
converts the value to a signed number of halfwords relative to the current location
counter, and then uses that value in the object code. An absolute value may be
used for a relative address, but the assembler issues a warning message, as it
uses the supplied value, and this may cause unpredictable results.
88 HLASM V1R5 Language Reference