Appendix G: Writing Utilities - HP 9835A Programming Manual

Appendix
G
Writing Utilities
A utility, essentially, is a "special" assembly language subroutine. What makes it special is a set
of instructions which keeps it from being displayed when a program is being stepped through
using the
mID
key. This provides some manner of security for the code in the routine from the
casual user.
The following must be done to make a section of code into a utility -
1. The entry point for the utility must consist of the instruction -
2. Each exit point from the utility must consist of the following instructions -
·!····i:· ..
········:=
.LJ .::::: I::~
..
i::;;:<i:::·····-;--·
n (n may be any number, - 32 through
+
31, dep~nding upon the desired
returning point)
For example, here is a simple utility to increment a private counter -
::;DLiF:C:F
::::;OUPCF
':::DUF:CE: ~:ET
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