upd70f3017ay Renesas Electronics Corporation., upd70f3017ay Datasheet - Page 61

• Manufacturer Part Number: upd70f3017ay
• Description: V850/sa1tm 32-/16-bit Single-chip Microcontroller
• Manufacturer: Renesas Electronics Corporation.

3.2.1 Program register set
(1) General-purpose registers
(2) Program counter (PC)
After reset: 00000000H
Symbol
The program register set includes general-purpose registers and a program counter.
PC
Thirty-two general-purpose registers, r0 to r31, are available. Any of these registers can be used as a data
variable or address variable.
However, r0 and r30 are implicitly used by instructions, so care must be exercised when using these registers.
Also, r1, r3 to r5, and r31 are implicitly used by the assembler and C compiler. Therefore, before using these
registers, their contents must be saved so that they are not lost. The contents must be restored to the registers
after the registers have been used. r2 is sometimes used by the real-time OS. When the real-time OS to be
used is not using r2, r2 can be used as a variable register.
This register holds the address of the instruction under execution. The lower 24 bits of this register are valid, and
bits 31 to 24 are fixed to 0. If a carry occurs from bit 23 to bit 24, it is ignored.
Bit 0 is fixed to 0, and branching to an odd address cannot be performed.
Note Area in which program code is mapped.
r0
r1
r2
r3
r4
r5
r6 to r29
r30
r31
PC
31
Name
Fixed to 0
Zero register
Assembler-reserved register
Address/data variable register (when the real-time OS to be used is not using r2)
Stack pointer
Global pointer
Text pointer
Address/data variable registers
Element pointer
Link pointer
Program counter
Usage
24
Table 3-1. Program Registers
CHAPTER 3 CPU FUNCTIONS
23
User’s Manual U12768EJ4V1UD
Always holds 0
Working register for generating 32-bit immediate
Used to generate stack frame when function is called
Used to access global variable in data area
Register to indicate the start of the text area
Base pointer when memory is accessed
Used by compiler when calling function
Holds instruction address during program execution
Instruction address under execution
Operation
Note
1
0
0
61