Address Modes

As mentioned on the Instructions page, address modes specify algorithms for finding the values to be operated on. Any value that an instruction manipulates is generally either in memory or in a register. If it is in a register, then register mode is used to access it. In this case the address mode simply names the register that contains the value. If it is in memory, then the CPU must calculate the effective address, which is the address in memory that actually contains the value. Often the instruction will not contain the effective address, but instead will contain the information needed to calculate it.

We will look at some examples: