Siemens plc indirect addressing method, the main mentioned in this article is Siemens S7-300plc.
1. The highest bit (31st bit) of the indirect addressing pointer in the area is 0. When the value is 0, it is the indirect addressing in the area. At this time, the area identification number rrr is also 0, and the format of the address pointer is the same as the memory indirect addressing. The following are examples of indirect addressing in the region:
LP#5.0 //Load the pointer of the indirect addressing into the accumulator 1
LAR1 //Send the contents of accumulator 1 to AR1
AM[AR1, P#2.3] //P#5.0 in AR1 plus offset P#2.3, operate on M7.3
= Q[AR1, P#0.2] //The result of the logical operation is sent to Q5.2, P#5.0+P#0.2=P#5.2
L MW[AR1, P#19.0] //Load MW24 into accumulator 1
The square brackets are the address of the operand, which is equal to the address value P#5.0 in AR1 plus the address offset after the comma. For example, the address of the operand in the third instruction is P#5.0+P#2.3=P# 7.3, that is, the operand is M7.3.
2. The most significant bit (31st bit) of the indirect addressing pointer between the regions is the indirect addressing between the regions when x = 1, and the following is an example of indirect addressing between regions:
LP#M 6.0 //Load the double word address of M6.0 into the accumulator 1
LAR1 //Send the contents of accumulator 1 to AR1
LW [AR1, P#20.0] //Transfer the contents of MW26 to accumulator 1
The binary number corresponding to P#M6.0 is 2#1000 0011 0000 0000 0000 0000 0011 0000. Since the address pointer P#M6.0 already contains the area information (rrr=2#011 indicates the M area), the third instruction "LW[AR1, P#50.0]" does not need to use the address identifier M again.
When reading, writing a word, byte or double word with the address pointer, the bit number to the right of the decimal point in the pointer must be 0, otherwise an error will occur.
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