SMB0 Status Bits

Special Memory Byte 0 (SM0.0 - SM0.7) provides eight bits that are updated by the S7-200 CPU at the end of each scan cycle. You can use these bits to invoke functions in your program.

SM Bits

(Read Only)

Description

SM0.0 This bit is always on.
SM0.1 This bit is on for the first scan cycle. One use is to call an initialization subroutine.
SM0.2 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.
SM0.3 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.
SM0.4 This bit provides a clock pulse that is on for 30 seconds and off for 30 seconds, for a cycle time of 1 minute. It provides an easy-to-use delay or a 1-minute clock pulse.
SM0.5 This bit provides a clock pulse that is on for 0.5 seconds and then off for 0.5 seconds for a cycle time of 1 second. It provides an easy-to-use delay or a 1-second clock pulse.
SM0.6 This bit is a scan cycle clock that is on for one scan and then off for the next scan. This bit can be used as a scan counter input.
SM0.7 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.