SH7727 datasheet(97/1109 Pages) RENESAS

97 / 1109 page

Section 2 CPU

Rev. 5.00 Dec 12, 2005 page 25 of 1034

REJ09B0254-0500

2.1.1

General Purpose Registers

There are sixteen 32-bit general registers (Rn), designated R0 to R15. The general registers are

used for data processing and address calculation.

With SuperH microcomputer type instructions, R0 is used as an index register. With a number of

instructions, R0 is the only register that can be used. R15 is used as the stack pointer (SP). In

exception handling, R15 is used to reference the stack when saving and restoring the status register

(SR) and program counter (PC).

With DSP type instructions, eight of the sixteen general registers are used for addressing of X and

Y data memory and data memory (single data) that uses the L-bus.

To access X memory, R4 and R5 are used as X address register [Ax] and R8 is used as X index

as Y index register [Iy]. To access single data that uses the L-bus, R2, R3, R4, and R5 are used as

single data address register [As] and R8 is used as single data index register [Is].

Figure 2.3 shows the general purpose registers, which are identical to SH-3’s, when DSP

extension is disabled.

R0*1 *2

R1*2

R2*2

R3*2

R4*2

R5*2

R6*2

R7*2

R10

R11

R12

R13

R14

R15

General Registers (when not in DSP mode)

Notes: 1. R0 functions as an index register in the

indexed register-indirect addressing mode

and indexed GBR-indirect addressing mode.

In some instructions, only R0 can be used as

the source register or destination register.

2. R0 to R7 are banked registers. In user mode,

BANK0 is used. In privileged mode, SR.RB

specifies BANK.

SR.RB = 0; BANK0 is used

SR.RB = 1; BANK1 is used

Figure 2.3 General Purpose Register (Not in DSP Mode)

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