Siemens S7 - Indirect addressing classification introduced - 300

Addressing in the PLC controller can be divided into direct addressing and indirect addressing two parts, the direct addressing is directly by instructions in a program to access the address, the address is usually a constant, such as T0 timer, address is '0'. And indirect addressing, address stored with address pointer, the address is a variable, when the program execution to determine the actual address, such as the timer T [ MW0] 。 If MW0 values equal to zero, then said to T0, if MW0 value is equal to 1, T1.

S7 - Indirect addressing in 300 can be divided into the following categories:

1, the memory indirect addressing

1) 16-bit address pointer

2) The inner regions of the 32-bit pointer address

2, register indirect addressing

1) The inner regions of the 32-bit pointer address

2) A 32-bit pointer to cross area addressing

then respectively introduce the several indirect addressing pointer address as the address format, access format and the usage of each type of indirect addressing mode.

memory indirect addressing:

memory in memory address pointer is divided into 16 address pointer and 32 to address pointer, allows storage memory pointer to a memory address ( M） , a local variable storage ( L） And data blocks ( DB) 。

16 pointer address:

16 address pointer application at the timer ( T） And counter ( C) , block ( OB, FB, FC, DB) Addressing, the serial number of the indirect addressing mode in the process of practical application is relatively small.

pointer format for:

the pointer to a 16-bit memory space, according to the value of the storage space for many, the address of the corresponding number is how much.

address addressing format is expressed as: regional operator said [ A 16-bit address pointer] , such as the DB [ MW0] , if the value is equal to 10 MW0, says is the DB for DB10.

, shown in the following procedure describes the use of A 16-bit registers the addressing mode on A visit to A timer:

10 L T 'MW10' / / put the number 10 in to A 16-bit memory do as instructions

A 'I0. 0 '/ / start the normally open contact signal state s5t # 10 s

L

SD T [ ' MW10 '] / / using a 16-bit memory pointer as the serial number of the timer, timer setting time for 10 s.

A T [ ' MW10 ']

=”。 0 '/ / take timer normally open contact state output a signal output.

can be seen from the example, the address pointer storage and MW10, use only need to modify the data of MW10, can visit different number of timers.

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