Tormach PCNC 440 - Page 142

Chapter 7
142
UM10372_PCNC440_Manual_0221A
PROgRAMMiNg
Parameter Scope
The scope of a parameter is either global or local within a subroune. The scope of each parameter is
inferred from its syntax. Subroune parameters and named local parameters have local scope. Named
global parameters and all numbered parameters starng from #31 are global in scope. RS274/NGC uses
lexical scoping. In a subroune only the local parameters dened therein, and any global parameters
are visible. The local parameters of a calling procedure are not visible in a called procedure.
Behavior of Uninialized Parameters
Uninialized global parameters and unused subroune parameters return the value zero when used
in an expression. Uninialized named parameters signal an error when used in an expression.
Parameter Mode
The mode of a parameter can either be read/write or read-only. Read/write parameters may be
assigned values within an assignment statement. Read-only parameters cannot be assigned values.
They may appear in expressions, but not on the le-hand side of an assignment statement.
Persistence and Volality
Parameters can either be persistent or volale. When the operang system is powered o, volale
parameters lose their values and are reset to zero. The values of persistent parameters are saved in
a disc le and restored to their previous values when the operang system is powered on again. All
parameters except numbered parameters in the current persistent range (5163 to 5390) are volale.
Intended Usage
Numbered parameters in the range #31-#5000, named global, and local parameters are available
for general-purpose storage of oang-point values, like intermediate results, ags, etc., throughout
program execuon. They are read/write (can be assigned a value). Subroune parameters,
numbered parameters #1-#30, and system parameters are read-only and not available for general
use. Subroune parameters are used to hold the actual parameters passed to a subroune.
Numbered parameters in the range of #1-#30 are used to access osets of coordinate systems.
System parameters are used to determine the current running version and are read-only.