In this case, the address after being modified by the selected index register is used to locate the indirect address.
The indirect address can be acted on by an index register and deferred again if desired.
This new address is known as the indirect address for the instruction and will be used -9-to locate the operand.
An instruction which is to use an indirect address will have a ONE in bit six of the instruction word.
An addressing mode found in many processors' instruction sets where the instruction contains the address of a memory location which contains the address of the operand (the "effective address") or specifies a register which contains the effective address. In the first case (indirection via memory), accessing the operand requires two memory accesses - one to fetch the effective address and another to read or write the actual operand. Register indirect addressing requires only one memory access.
An indirect address may be indicated in assembly language by an operand in parentheses, e.g. in Motorola 68000 assembly
writes the contents of register D0 to the location pointed to by the address in register A0.
Indirect addressing is often combined with pre- or post- increment or decrement addressing, allowing the address of the operand to be increased or decreased by one (or some specified number) either before or after using it.