Page 186 - DCAP210_INTRODUCTION__TO_MICROPROCESSORS

Introduction to Microprocessors

Notes pending condition handler information

call/signal on : error, failure, halt, notready, novalue, syntax
pending condition information
information that is returned by the condition built-in function
settings associated with the options instruction

elapsed time clock
a function or subroutine can alter the setting of the elapsed time clock, which is provided by the
time built-in function, without affecting the setting that is used in the calling procedure.

trace settings
a function or subroutine can alter trace settings, which are established by the trace instruction or
the trace built-in function, without affecting the settings that are used in the calling procedure.

Support for the options instruction is implementation-dependent, and the
settings may not be saved and restored during function or subroutine calls.

13.3.2 Trap subroutine call activation/deactivation
call ON conditionName [ NAME trapLabel ]

call OFF conditionName
The call ON or OFF instructions activate or deactivate the handling of condition traps by an
associated procedure. When active, a conditional trap will cause the trapLabel to be invoked as a
subroutine. In a call ON instruction, if the trapLabel is absent, the label that is invoked is the
same as the condition name. The handling of condition traps can alternatively be activated or
deactivated by the signal ON or OFF instructions.
The conditionName in the call ON or OFF is one of the following:

ERROR
FAILURE
HALT
NOTREADY
Unlike the signal ON or OFF trap anticipation instructions, the following condition names are
ineligible in a call ON or OFF instruction:
SYNTAX
NOVALUE

The call ON or OFF instructions activate or deactivate the handling of condition
traps by an associated procedure.

13.4 Return Instruction

In computer programming, a return statement causes execution to leave the current subroutine
and resume at the point in the code immediately after where the subroutine was called, known as
its return address. The return address is saved, usually on the process's call stack, as part of the
operation of making the subroutine call. Return statements in many languages allow a function
to specify a return value to be passed back to the code that called the function.

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