MIPS R4000 Microprocessor User's Manual 13
Introduction
Two of the CPU general purpose registers have assigned functions:
• r0 is hardwired to a value of zero, and can be used as the target
register for any instruction whose result is to be discarded. r0
can also be used as a source when a zero value is needed.
• r31 is the link register used by Jump and Link instructions. It
should not be used by other instructions.
The CPU has three special purpose registers:
• PC — Program Counter register
• HI — Multiply and Divide register higher result
• LO — Multiply and Divide register lower result
The two Multiply and Divide registers (HI, LO) store:
• the product of integer multiply operations, or
• the quotient (in LO) and remainder (in HI) of integer divide
operations
The R4000 processor has no Program Status Word (PSW) register as such;
this is covered by the Status and Cause registers incorporated within the
System Control Coprocessor (CP0). CP0 registers are described later in
this chapter.
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