Two Register Addressing
This addressing mode uses the values contained in two registers in order to generate an address. The two values are added together to create the address, which is then used to load or store a value from/to memory. These addresses are a full 32 bits wide.
Register Plus Immediate Addressing
This addressing mode makes use of a 32-bit value from a register together with a sign-extended 13-bit immediate value. These two components are added together to give the effective address. As a special case of this addressing mode, the zero register g0 can be used, giving a 13-bit immediate addressing mode that can be used to access the upper and lower 4kB of memory (effectively this is like an absolute addressing mode for these regions of memory). This is the simplest addressing mode since no registers need to be specially set up beforehand.