• This is large enough to handle the offset in a typical lw or sw, plus a vast majority of values that will be used in the slti instruction. Operation beq s, t, label if (s t) pc + i << 2 bgtz s, label if (s > 0) pc + i << 2.

16 bits can be used to represent immediate up to 2 16 different values.MIPS III added 64 bit capabilities - but with the core 32 bit architecture as a subset, and MIPS IV expanded on this. The MIPS I and II ISAs were 32 bit architectures. addi, slti, slitu, the immediate is sign-extended to 32 bits. Each successive ISA is a superset of the preceding one - so anything found in MIPS I is also found in MIPS II, III, and IV, etc.Rt: specifies register which will receive result of computation (this is why it’s called the target register “rt”) Rs: specifies the only register operand (if there is one) (This is a somewhat simplified view, but sufficient for now). Each cycle executes one machine instruction. This also answers question of why R-format has two 6-bit fields to identify instruction instead of a single 12-bit field: in order to be consistent with other formats. The MIPS endlessly cycles through three basic steps.

Opcode: same as before except that, since there’s no funct field, opcode uniquely specifies an I-format instruction Most importantly, opcode is still in same location. Only one field is inconsistent with R-format. First notice that, if instruction has immediate, then it uses at most 2 registers.ĭefine “fields” of the following number of bits each:.Ideally, MIPS would have only one instruction format (for simplicity): unfortunately, we need to compromiseĭefine new instruction format that is partially consistent with R-format:.5-bit field only represents numbers up to the value 31: immediates may be much larger than this.

Mips iformat