NEC Network Controller uPD98502 - Manual (Page 59)

CHAPTER 2 V R 4120A
Preliminary User’s Manual S15543EJ1V0UM 59
2.1.2 V R 4120A registers
The V R 4120A has the following registers.
— general-purpose register (GPR): 64 bits × 32
In addition, the processor provides the following special registers:
— 64-bit Program Counter (PC)
— 64-bit HI register, containing the integer multiply and divide upper doubleword result
— 64-bit LO register, containing the integer multiply and divide lower doubleword result
Two of the general-purpose registers have assigned the following 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 link instruction, such as JAL (Jump and Link) instructions. This register can be
used for other instructions. However, be careful that use of the register by a link instruction will not coincide
with use of the register for other operations.
The register group is provided within the CP0 (system control coprocessor), to process exceptions and to manage
addresses.
CPU registers can operate as either 32-bit or 64-bit registers, depending on the V
R
4120A processor operation
mode.
Figure 2-2 shows the CPU registers.
Figure 2-2. V R 4120A Registers
General-purpose register
r0 = 0
0 31 Multiply/divide register 32 63
HI
0 31 32 63
LO
Program Counter
0
PC
0
63
63
r1
r2
⋅
⋅
⋅
⋅
r29
r30
r31 = LinkAddress
31 32
31 32
The V R 4120A 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).
The CP0 registers are used for exception handling or address management. The overview of these registers is
described in 2.1.5 Coprocessors (CP0).