Siemens Simatic S7 Series System Manual

PLC concepts
4.2 Accessing data
S7-200 SMART
System Manual, 09/2015, A5E03822230-AC
71
Entering an asterisk (*) in front of an operand for an instruction specifies that the operand is
a pointer. As shown in the following figure, entering *AC1 means that AC1 stores a pointer to
the word-length value being referenced by the Move Word (MOVW) instruction. In this
example, the values stored in both VB200 and VB201 are moved to accumulator AC0.
①
MOVD &VB200, AC1
Creates the pointer by moving the address of VB200 (initial byte of VW200) to AC1
②
MOVW *AC1, AC0
Moves the word value referenced by the pointer in AC1
Figure 4-7 Creating and using a pointer
As shown in the following figure, you can change the value of a pointer. Since pointers are
32-bit values, use double-word instructions to modify pointer values. Simple mathematical
operations, such as adding or incrementing, can be used to modify pointer values.
①
MOVD &VB200, AC1
Creates the pointer by moving the address of VB200 (initial byte of VW200) to AC1
MOVW *AC1, AC0
Moves the word value referenced by the pointer in AC1
②
+D +2, AC1
Adds 2 to the accumulator to point to the next word location
MOVW *AC1, AC0
Moves the word value referenced by the pointer in AC1
Figure 4-8 Modifying a pointer

Siemens Simatic S7 Series Specifications

General

CPU	Varies by model (e.g., S7-300, S7-400, S7-1200, S7-1500)
Communication Interfaces	PROFIBUS, PROFINET, Ethernet, MPI
Programming	TIA Portal, STEP 7
Programming Languages	LAD, FBD, STL, SCL, GRAPH
I/O Modules	Digital, Analog, Specialty modules available
Operating Temperature	0°C to 60°C (standard models)
Mounting	DIN rail mounting
Operating Voltage	24V DC or 120/230V AC (varies by model)
Protection Class	IP20 (standard models)
Memory	Varies depending on the S7 model. Includes work memory (RAM) for program execution, load memory (EEPROM or Flash) for program storage, and system memory for operating system functions. Memory sizes range from kilobytes to megabytes.