References; Often-Used Special Memory Bits; E.1 Often-Used Special Memory Bits - Siemens SIMATIC S7 System Manual

References

E.1

Often-used special memory bits

The complete list of pre-defined special memory program symbols is available to your
project, in the System Symbol table.
Table E- 1 Often-used special memory bits
SM address System symbol name
SM0.0 Always_On
SM0.1 First_Scan_On
SM0.2 Retentive_Lost
SM0.3 RUN_Power_Up
SM0.4 Clock_60s
SM0.5 Clock_1s
SM0.6 Clock_Scan
SM0.7 RTC_Lost
SM1.0 Result_0
SM1.1 Overflow_Illegal
SM1.2 Neg_Result
SM1.3 Divide_By_0
SM1.4 Table_Overflow
SM1.5 Table_Empty
SM1.6 Not_BCD
SM1.7 Not_Hex
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
Description
This bit is always TRUE.
The CPU sets this bit to TRUE, for the first scan cycle, and sets it to FALSE
thereafter. One use for this bit is to call an initialization subroutine.
TRUE for one scan cycle if retentive data is lost
TRUE for one scan cycle when RUN mode is entered from a power-up condition
Clock pulse that is TRUE for 30 s, OFF for 30 s, for a cycle time of 1 min.
Clock pulse that is TRUE for 0.5 s, OFF for 0.5 s, for a cycle time of 1 s.
Scan cycle clock that is TRUE for one scan cycle and OFF for the next scan
cycle
For CPU models that have a real-time clock, the CPU sets this bit TRUE for one
scan cycle if the time on the real-time clock device was reset or lost at power up.
The program can use this bit as either an error memory bit or to invoke a special
start-up sequence.
Set to TRUE by the execution of certain instructions when the result of the op-
eration = 0
Set to TRUE by the execution of certain instructions on overflow or illegal numer-
ic value
Set to TRUE when a math operation produces a negative result
Set to TRUE when an attempt is made to divide by zero
Set to TRUE when the Add to Table instruction attempts to overfill the table
Set to TRUE when a LIFO or FIFO instruction attempts to read from an empty
table
Set to TRUE when an attempt is made to convert a non-BCD value to a binary
value
Set to TRUE when an ASCII value cannot be converted to a valid hexadecimal
value
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