2-24 Series 90-30/20/Micro Programmable Controllers Reference Manual – September 1998 GFK-0467K
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System Status References System status references in the Series 90 PLC are assigned to %S, %SA, %SB, and %SC memory.
They each have a nickname. Examples of time tick references include T_10MS, T_100MS,
T_SEC, and T_MIN. Examples of convenience references include FST_SCN, ALW_ON, and
ALW_OFF.
Note
%S bits are read-only bits; do not write to these bits. You may, however, write to
%SA, %SB, and %SC bits.
Listed below are available system status references, which may be used in an application program.
When entering l ogic, either the reference or th e n ickname can be used. Refer to chapter 3 , “Fault
Explanations and Correction,” for more detailed fault descriptions and information on correcting
the fault.
You cannot use these special names in another context.
Table 2-6. System Status References
Reference Nickname Definition
%S0001 FST_SCN Set to 1 when the current sweep is the first sweep.
%S0002 LST_SCN Reset from 1 to 0 when the current sweep is the last sweep.
%S0003 T_10MS 0.01 second timer contact.
%S0004 T_100MS 0.1 second timer contact.
%S0005 T_SEC 1.0 second timer contact.
%S0006 T_MIN 1.0 minute timer contact.
%S0007 ALW_ON Always ON.
%S0008 ALW_OFF Always OFF.
%S0009 SY_FULL Set when the PLC fault table fills up. Cleared when an entry is
removed from the PLC fault table and when the PLC fault table is cleared.
%S0010 IO_FULL Set when the I/O fault table fills up. Cleared when an entry is
removed from the I/O fault table and when the I/O fault table is cleared.
%S0011 OVR_PRE Set when an override exists in %I, %Q, %M, or %G memory.
%S0013 PRG_CHK Set when background program check is active.
%S0014 PLC_BAT Set to indicate a bad battery in a Release 4 or later CPU. The
contact reference is updated once per sweep.