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Assembly Language Fundamentals 79
Utilities
A number of utilities have been provided to help make your programming tasks easier and to
give you direct access to some of the operating system's capabilities and routines.
Descriptions of the utilities are made in conjunction with those topics where the utilities playa
part. The form of the description of a utility is somewhat standardized. Each description will tell
you-
• The name of the utility.
• The general procedure for using the utility.
• Any special requirements which must be satisfied for the utility to work properly.
• A step-by-step calling procedure for the utility.
• The exit conditions.
Utilities are a form of subroutine, so to execute them it is necessary to execute a jump-to-
subroutine instruction (JSM)
if
you want the utility to return to the routine which calls it. Most
utilities execute a RET 1 instruction to return, so in some cases where you follow a utility call
with a RET 1 of your own, you can save the RET instruction by
usi~g
the JMP (unconditional
branch) instruction instead. For example, a typical utility call looks like -
t.. ••••
ux::
but
if
it happened to be followed by a RET 1 -
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