Get Step 7 Indirect Addressing Pdf

Indirect addressing may be used for code or data. It can make implementation of pointers, references, or handles much easier, and can also make it easier to call subroutines which are not otherwise addressable. Indirect addressing does carry a performance penalty due to the extra memory access involved.

Indirect Addressing allows us to write the logic one time, and feed a different index into the logic. This index would tell the logic which tank to perform the calculations on. Another example would be a fault log. Each time a fault occurs, we want to log the system time to a different memory location.

The direct addressing mode contains the concerned operand in the instruction code's address field. In the case of an indirect addressing mode, the operand's address stays in the address field of any instruction. It requires no memory references for accessing the data.

Indirect addressing is good to repeat a program code for several times but with different values. Then you can create a step counter and the counter value will be the base of the indirect address to load different values. You have an axis e.g. which has to be moved to different positions in a sequence.

In direct addressing mode, the actual address of the data is mentioned in the instructions itself. On the other hand, indirect addressing mode contains the effective address of the memory location where the actual address of the data resides.

Indirect Addressing allows us to write the logic one time, and feed a different index into the logic. This index would tell the logic which tank to perform the calculations on. Another example would be a fault log. Each time a fault occurs, we want to log the system time to a different memory location.

with direct addressing your program is "static" (at every plc cycle the same address is processed). with indirect addressing you can create "dynamic" program (at every plc cycle address can change).