Renesas SH7641 - Manual (Page 79)

Section 2 CPU
Rev. 4.00 Sep. 14, 2005 Page 29 of 982
REJ09B0023-0400
2.1.1 General 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.
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 the X address register [Ax] and R8 is used as the X
index register [Ix]. To access Y memory, R6 and R7 are used as the Y address register [Ay] and
R9 is used as the Y index register [Iy]. To access single data that uses the L-bus, R2, R3, R4, and
R5 are used as the single data address register [As] and R8 is used as the single data index register
[Is].
Figure 2.3 shows the general registers, which are identical to those of the SH3, when DSP
extension is disabled.
31
R0* 1, * 2
R1* 2
R2* 2
R3* 2
R4* 2
R5* 2
R6* 2
R7* 2
R8
R9
R10
R11
R12
R13
R14
R15
0
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. SR.RB specifies
BANK.
SR.RB = 0; BANK0 is used
SR.RB = 1; BANK1 is used
Figure 2.3 General Registers (Not in DSP Mode)