Specifications

CPU Memory: Data Types and Addressing Modes
5-5
S7-200 Programmable Controller System Manual
C79000-G7076-C233-01
Addressing the Variable (V) Memory Area
You can use V memory to store intermediate results of operations being performed
by the control logic in your program. You can also use V memory to store other
data pertaining to your process or task. You can access the V memory area in bits,
bytes, words, or double words.
Format:
Bit V [byte address].[bit address] V10.2
Byte, Word, Double Word V [size][starting byte address] VW100
Addressing the Bit Memory (M) Area
You can use the bit memory area (M memory) as control relays to store the
intermediate status of an operation or other control information. While the name
“bit memory area” implies that this information is stored in bit-length units, you can
access the bit memory area not only in bits, but also in bytes, words, or double
words.
Format:
Bit M [byte address].[bit address] M26.7
Byte, Word, Double Word M [size][starting byte address] MD20
Addressing the Sequence Control Relay (S) Memory Area
Sequence Control Relay bits (S) are used to organize machine operations or steps
into equivalent program segments. SCRs allow logical segmentation of the control
program. You can access the S bits as bits, bytes, words, or double words.
Format:
Bit S [byte address].[bit address] S3.1
Byte, Word, Double Word S [size][starting byte address] SB4
Addressing the Special Memory (SM) Bits
The SM bits provide a means for communicating information between the CPU and
your program. You can use these bits to select and control some of the special
functions of the S7-200 CPU, such as:
 A bit that turns on for the first scan cycle
 Bits that toggle at fixed rates
 Bits that show the status of math or operational instructions
For more information about the SM bits, see Appendix C. While the SM area is
based on bits, you can access the data in this area as bits, bytes, words, or double
words.
Format:
Bit SM [byte address].[bit address] SM0.1
Byte, Word, Double Word SM [size][starting byte address] SMB86