Generic Addressing Modes:

[ Key phrases are "Memory-Address" vs. "Contents-of-Memory" ]

Please understand that as CPU manufacturers come out with their versions of various CPU's, and system software companies present their machine codes for same, they sometimes "re-define" these descriptions (the wording) to suit what they think are appropriate definitions of the addressing method. The descriptions given here only serve one purpose, and that is to help folks understand "the basics" of CPU addressing modes. Also, that these given modes can sometimes be combined in various fashions, which can result in some very complex and powerful memory access methods.

 Absolute: To a specific address location. (Sometimes referred to as General Addressing)
 Immediate: The method of loading the specific value(s) following the Op-Code. The next Immediate-Value(s), that follow, or a part of, the given instruction.
 Relative: A location that is forward or backward, relative (+/-) to, or from, the current location.
 Indirect: To a specific address location, that is identified as an address value, contained within another, as Contents of an Address, used as a "Forwarding Address" to another address location (as an Indirect Location)
 Register: To a specific address location, specified by the contents of a register.
 Indexed: A specific form of Register Addressing, with provision for an additive "Offset" of the specified address, allowing variable "Indexing" from the "Base Address" within the Index-Register.
 Pre-Indexed:
A combination addressing method, incorporating Indexed Addressing prior to the use of Indirect Addressing.
 Post-Indexed:
 A combination addressing method, incorporating Indexed Addressing after the use of Indirect Addressing.
 Page:  A form of addressing related to specific "Pages" or "Blocks" of memory.
 Base Page:
 Page Addressing restricted to specifically the "Base-Page" of memory.
 Extended: A form of memory addressing that allows for an extension beyond the normal range of addressing.
 Internal: Any form of activity that is only within the CPU, and does not affect outside devices or memory.
 I/O: Where Address Lines are used for "Device Address" in all cases.
Port Mapped I/O:
I/O Device Addressing in conjunction with "IOREQ" type of signals.
Memory Mapped I/O:
I/O Device Addressing in conjunction with conventional "MREQ" type of signals.

Generic.html - SfE-DCS ... ddf - 06/06/2013