UPD70732 Datasheet, PDF (13/66 Pages) NEC – V810TM 32-BIT MICROPROCESSOR

µPD70732
2.1 Program Register Set
The program register set is composed of general-purpose registers and a program counter.
(1) General-purpose registers
Thirty-two general-purpose registers, r0 to r31, are available. All these registers can be used as data
registers or address registers.
Of these registers, r0 and r26 through r30 are implicitly used by some instructions, and r1 through r5 and
r31 are implicitly used by the assembler and C compiler. Therefore, when using these registers, it is
necessary to take special care such as saving these registers’ contents to different areas before using
these registers and restoring the contents after using them.
Register
r0
r1
r2
r3
r4
r5
r6 to r25
r26
r27
r28
r29
r30
r31
Table 2-1. Program Registers
Application
Zero register
Register reserved for assembler
Handler stack pointer
Stack pointer
Global pointer
Text pointer
—
String destination bit offset
String source bit offset
String length register
String destination address register
String address register
Link pointer
Operation
Always holds zeros.
Used as a working register to generate a 32-bit immediate data.
Used as the stack pointer for the handler.
Used to generate a stack frame at a function call.
Used to access a global variable in the data area.
Points the start address of the text area.
Stores address or data variables.
Used in a bit-string instruction execution.
Stores the return address at execution of a JAL instruction.
(2) Program Counter
The program counter (PC) indicates the address of the instruction currently executed by the program.
Bit 0 of the PC is fixed to 0, and execution cannot branch to an odd address. The contents of the PC
are initialized to FFFFFFF0H at reset.
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