Addressing Modes

In the Guin-16, addressing modes are used to tell the CPU where in memory it can find the data to be used in a given instruction. This allows for data to be stored separately from the instruction stream rather than needing the data for a given instruction to be stored sequentially in memory.

Implicit

Addressing Code: x0

For many instructions in the Guin-16, there is not extra data required to perform the instruction. An implicit addressing mode denotes this case and immediately performs the instruction.

Immediate

Addressing Code: x0

If an instruction uses immediate mode, it will use the word in the memory address directly ahead of it as a data word. Although Immediate shares an addressing code with Implicit, the type of instruction will determine which is used. An instruction using an implicit addressing mode will already have completed before an immediate instruction processes.

PageAhead

Addressing Code: x5

PageAhead mode tells the CPU to fetch the address exactly x pages ahead the current instruction's address to use as a data word, where x is specified by the Page Register

PageBehind

Addressing Code: x2

PageAhead mode tells the CPU to fetch the address exactly x pages behind the current instruction's address to use as a data word, where x is specified by the Page Register

Absolute

Addressing Code: x4

Absolute mode tells the CPU that the next word in memory is the address to the actual data to be used by the instruction.

AbsoluteX

Addressing Code x1

AbsoluteX mode tells the CPU to get the next word in memory and add it to the X Register to get the address of the data to use in the instruction.

AbsoluteY

Addressing Code x6

AbsoluteY mode tells the CPU to get the next word in memory and add it to the Y Register to get the address of the data to use in the instruction.

Indirect

Addressing Code x7

Indirect mode tells the CPU to use the next word as an address to a word in memory. This word is the address of the actual word of data to use. This addressing mode is only used by the JMP instruction.

Note: You can think of this as using absolute mode twice, once to get the address to use, and then again to get the actual data.