Using Pointers For Indirect Addressing - Siemens SIMATIC S7 System Manual

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PLC concepts

4.2 Accessing data

The following table provides an example of the fixed mapping convention (established by

STEP 7 Micro/WIN SMART and downloaded as part of the I/O configuration, in the system

CPU mapping convention

The CPU models CPU CR20s, CPU CR30s, CPU CR40s, and CPU CR60s do not support

the use of expansion modules or signal boards.

Using pointers for indirect addressing

Indirect addressing uses a pointer to access data in memory. Pointers are double word

memory locations that contain the address of another memory location. You can only use

V memory locations, L memory locations, or accumulator registers (AC1, AC2, AC3) as

pointers. To create a pointer, you must use the Move Double Word instruction to move the

address of the indirectly addressed memory location to the pointer location. Pointers can

also be passed to a subroutine as a parameter.

An S7-200 SMART CPU allows pointers to access the following memory areas: I, Q, V, M, S,

AI, AQ, SM, T (current value only), and C (current value only). You cannot use indirect

addressing to access an individual bit or to access HC, L or accumulator memory areas.

To indirectly access the data in a memory address, you create a pointer to that location by

entering an ampersand character (&) and the first byte of the memory location to be

addressed. The input operand of the instruction must be preceded with an ampersand (&) to

signify that the address of a memory location, instead of its contents, is to be moved into the

location identified in the output operand of the instruction (the pointer).

System Manual, V2.3, 07/2017, A5E03822230-AF

S7-200 SMART

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Simatic s7-200 smart