Still trying to understand the Adres Register

Hey,

An example code of S7:

LAR2 P#66.0 // Preset Basic Adres for AR2
L MW [AR2,P#9.0] // Call MW75, offset 9.0 + preset 66.0
T MW230 // Transfer the value of MW75 in MW230

Why and when do u use this ?


Second example:

LAR1 P#10.0
A M[AR1,P#200.6] // = M210.6
= Q [AR1,P#120.4] // = M130.4




Why using this sort of indirect adressing ?

Combo, actually the examples that you gave really aren't good examples of indirect addressing. If you are loading an absolute address into AR2 (i.e. P#66.0), then all of the benefits of indirect addressing are lost. The only real advantage in this case is that if the address offset of your variables changes for some reason you would only have to change AR2, but there are much better ways to handle that.

Normally, AR2 (or AR1) would be calculated dynamically, which would allow you to point to data indirectly instead of hard-coding every possible situation. Take a look at some of the many examples on this site, and you will see some real-world applications.