Special Memory (Sm) Bits; Smb0: Status Bits; Special Memory Byte Smb0 (Sm0.0 To Sm0.7) - Siemens SIMATIC S7-200 System Manual

Special Memory (SM) Bits

Special memory bits provide a variety of status and control functions, and also
serve as a means of communicating information between the CPU and your
program. Special memory bits can be used as bits, bytes, words, or double words.

SMB0: Status Bits

As described in Table C-1, SMB0 contains eight status bits that are updated by the
S7-200 CPU at the end of each scan cycle.
Table C-1
SM Bits
SM0.0
SM0.1
SM0.2
SM0.3
SM0.4
SM0.5
SM0.6
SM0.7
S7-200 Programmable Controller System Manual
A5E00066097-02

Special Memory Byte SMB0 (SM0.0 to SM0.7)

This bit is always on.
This bit is on for the first scan cycle. One use is to call an initialization
subroutine.
This bit is turned on for one scan cycle if retentive data was lost. This bit can
be used as either an error memory bit or as a mechanism to invoke a special
startup sequence.
This bit is turned on for one scan cycle when RUN mode is entered from a
power-up condition. This bit can be used to provide machine warm-up time
before starting an operation.
This bit provides a clock pulse that is on for 30 seconds and off for 30
seconds, for a duty cycle time of 1 minute. It provides an easy-to-use delay, or
a 1-minute clock pulse.
This bit provides a clock pulse that is on for 0.5 seconds and then off for 0.5
seconds, for a duty cycle time of 1 second. It provides an easy-to-use delay
or a 1-second clock pulse.
This bit is a scan cycle clock which is on for one scan cycle and then off for
the next scan cycle. This bit can be used as a scan counter input.
This bit reflects the position of the Mode switch (off is TERM position, and on
is RUN position). If you use this bit to enable Freeport mode when the switch
is in the RUN position, normal communication with the programming device
can be enabled by switching to the TERM position.
Description (Read Only)
C
C-1