3.1 Basic Functionality
Registers
3-23
Precautions When Using Local Registers within a User Function
When you call a user function, consider what values could be in the local registers, and perform initializa-
tion as needed.
• Setting the D Register Clear When Start Option
1. Select File − Environment Setting from the MPE720 Version 7 Window.
2. Select Setup − System Setting.
3. Select Enable or Disable for the D Register Clear when Start option.
Disable: The initial values will be uncertain.
Enable: The initial values will be 0.
User functions can be called from any programs, any number of times.
Name Precautions
X registers (function
input registers)
If input values are not set, the values will be uncertain.
Do not use X registers that are outside of the range that is specified in the input defini-
tions.
Y registers (function
output registers)
If output values are not set, the values will be uncertain.
Always set the values of the range of Y registers that is specified in the output definitions.
Z registers (function
internal registers)
When the function is called, the previously set values will be lost and the values will be
uncertain.
These registers are not appropriate for instructions if the previous value must be retained.
Use them only after initializing them within the function.
# registers These are constant registers. Their values cannot be changed.
D registers
When the function is called, the previously set values are preserved.
If a previous value is not necessary, initialize the value, or use a Z register instead.
D registers retain the data until the power is turned OFF.
The default value after startup depends on the setting of the D Register Clear when
Start option.
Refer to the following sections for details.
Setting the D Register Clear When Start Option (page 3-23)
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