Parameters of POINTER type in Siemens TIA Portal

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A POINTER type parameter is a pointer that can point to a specific variable. It occupies 6 bytes (48 bits) in memory and may contain the following variable information:

Data block number or 0 (if no data is stored in the data block)

Memory area in the CPU

Variable address

The following figure shows the structure of the POINTER parameter type:

Pointer Types

According to the relevant information, the following four types of pointers can be declared using the POINTER parameter type:

Internal area pointer:

The internal area pointer stores the address information of the variable.

Cross-region pointers:

Cross-area pointers store the storage area and address information of variables.

DB pointer:

The DB pointer can be used to point to a data block variable. In addition to the variable's storage area and address information, the DB pointer also stores the data block number.

Zero pointer:

Using a zero pointer, you can indicate a missing value. A missing value can mean that the value does not exist, or that the value is unknown. A zero value indicates that a value is missing, but it is still a value.

The following table shows the format for declaring various pointer types:

Prefix P#

In the block call, the actual value is entered without the P# prefix as a formal parameter of the POINTER data type. It is then automatically converted to the POINTER format.

When using the prefix P# in the STL programming language, the following precautions must be observed:

Storage Area

The following table lists the hexadecimal codes for the memory areas of the POINTER parameter type:

Overview

Indirect addressing using pointers

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For indirect addressing, a specific data format is required, which should contain the address or also the range and data type of the operand. This data format is called a pointer. The following types of pointers can be used:

Reference (S7-1500)

VARIANT (S7-1200/1500)

POINTER (S7-1500)

ANY (S7-1500, only for blocks with standard access)

For more information about pointer data types, refer to See Also.

Example

The following example illustrates indirect addressing using a region pointer.

The pointer P#10.0 is passed to operand MD20. If operand MD20 is enclosed in square brackets during programming, it will be replaced by the address contained in the pointer during runtime.

Indirect addressing via pointers

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For indirect addressing, a specific data format is required, which should contain the address or also the range and data type of the operand. This data format is called a pointer. The following are pointer types:

POINTER (S7-300/400)

ANY (S7-300/400)

VARIANT (S7-1200/1500)

For more information about pointer data types, see the See Also section.

Example

The following example illustrates indirect addressing using intra-region pointers:

The pointer P#10.0 is passed to operand MD20. If operand MD20 is enclosed in square brackets during programming, it will be replaced by the address contained in the pointer during runtime.

LAR1: Load into AR1 with double word or area pointer

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With the "Load AR1 with double word or area pointer" instruction, you load the contents of a double word or an area-internal pointer or cross-area pointer into address register 1 (AR1). The contents of the double word must therefore match the format of the area pointer.

Pointers and double words can be addressed in one of the following memory areas:

Bit memory (M)

Temporary local data (L)

Data block (DB, DI)

The CPU will execute this instruction regardless of the result of the logic operation and the status bits. This instruction does not affect either the result of the logic operation or the status bits.

This instruction does not change the contents of the accumulator.

parameter

The following table shows the parameters for the "Load AR1 with double word or area pointer" instruction:

Example

The following example illustrates how this directive works: