Siemens Simatic S7 Series

Special memory (SM) and system symbol names
D.2 SMB0: System status
S7-200 SMART
System Manual, 09/2015, A5E03822230-AC
667
WARNING
Risks with STEP 7-Micro/WIN Version 4.0 or greater (.mwp files) with absolute special
memory (SM) addressing
If an earlier version of STEP 7-Micro/WIN (.mwp file) uses symbolic SM addressing in the
OB, and the System Symbols table is generated, the symbols will map properly to the new
addresses. However, if the .mwp file uses absolute SM addressing in the OB, those
absolute SM addresses will not map to the new SM addresses.
This incorrect mapping of SM addresses can result in unexpected machine or process
operation, which may cause death or serious injury to personnel, and/or damage to
equipment.
Delete the "S7-200 Symbols" table and generate a SMART "System Symbols" table. The
symbols in the OB will map to the new SM address scheme in the SMART System Symbols
table.
D.2
SMB0: System status
Special Memory Byte 0 (SM0.0 - SM0.7) provides eight bits that are updated by the S7-200
SMART CPU at the end of each scan cycle. Your program can read the status of these bits
and make decisions based on a bit's value.
Table D- 1 SMB0 system status bits
S7-200 SMART
symbol name
SM address
Description
Always_On
SM0.0
This bit is always ON. (set to 1)
First_Scan_On SM0.1 This bit is set ON, for the first scan cycle, and is set OFF thereafter. One use for this
bit is to call an initialization subroutine.
Retentive_Lost SM0.2 This bit is turned ON for one scan cycle after:
• Reset to factory communication command
• Reset to factory memory card evaluation
• Evaluation of program transfer card in which a new system block was loaded from
the card.
• Problem with retentive record on NAND flash
This bit can be used as either an error memory bit or as a mechanism to invoke a
special start-up sequence.
RUN_Power_Up SM0.3 This bit is turned ON for one scan cycle when RUN mode is entered from a power-up
or warm restart condition. This bit can be used to provide machine warm-up time
before starting an operation.
Clock_60s SM0.4 This bit provides a clock pulse that is OFF for 30 seconds and ON for 30 seconds, for
a cycle time of 1-minute. It provides an easy-to-use delay or a 1-minute clock pulse.
Clock_1s SM0.5 This bit provides a clock pulse that is OFF for 0.5 seconds and then ON for 0.5 sec-
onds for a cycle time of 1 second. It provides an easy-to-use delay or a 1-second
clock pulse.