Allen-Bradley LOGIX 5000 Reference Manual page 538

Chapter 11 Common Attributes for Advanced Process Control and Drives Instructions
538
Status Flags
Status Flag Description
(For CompactLogix 5380, CompactLogix 5480, ControlLogix
5580, Compact GuardLogix 5380, and GuardLogix 5580
controllers)
S:FS The first scan flag is set by the controller:
First scan flag • The first time a program is scanned after the controller goes to
Run mode
• The first time a program is scanned after the program is
uninhibited
• When a routine is called from an SFC Action and the step that
owns that Action is first scanned.
Use the first scan flag to initialize data for use in later scans. It is also
referred to as the first pass bit.
S:N The controller sets the negative flag when the result of a math or
logical operation is a negative value. Use this flag as a quick test for a
Negative flag
negative value.
S:Z The zero flag is set by the controller when the result of a math or
logical operation is zero. Use this flag as a quick test for a zero value.
Zero flag
The zero flag clears at the start of executing an instruction capable of
setting this flag.
Rockwell Automation Publication 1756-RM006K-EN-P - November 2018
Description
(For CompactLogix
5370, ControlLogix
5570, Compact
GuardLogix 5370,
and GuardLogix 5570
controllers)
The first scan flag is set
by the controller:
• The first time a
program is scanned
after the controller
goes to Run mode
• The first time a
program is scanned
after the program is
uninhibited
• When a routine is
called from an SFC
Action and the Step
that owns that
Action is first
scanned.
Use this flag to initialize
data for use in later
scans. It is also referred
to as the first pass bit.
The controller sets the
negative flag when the
result of a math or
logical operation is a
negative value. Use this
flag as a quick test for a
negative value.
Using S:N is more
efficient than using the
CMP instruction.
The controller sets the
zero flag when the
result of a math or
logical operation is zero.
Use this flag as a quick
test for a zero value.