SH7729R Datasheet, PDF (92/855 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer Super RISC engine Family/SH7700 Series

3. Increment address register addressing:
The Ax and Ay registers are address pointers. After a data transfer, they are each incremented
by 2 (post-increment).
There is an index register for each address pointer. The R8 register is the index register (Ix) for the
X memory address register (Ax), and the R9 register is the index register (Iy) for the Y memory
address register (Ay).
The X and Y data transfer instructions perform word-length processing, and use 16-bit access to
the X/Y data memory. A value of 2 is therefore added to the address register in the increment
processing. To perform decrementing, –2 is set in the index register and addition index register
addressing is specified. In X/Y data addressing, only bits 1 to 15 of the address pointer are valid.
When using X/Y data addressing, 0 must always be written to bit 0 of the address pointer and
index register.
X/Y data transfer addressing is shown in figure 2.12. When accessing X and Y memory using the
X and Y buses, the upper word of Ax (R4 or R5) and Ay (R6 or R7) is ignored. The result of
@AY+ or @Ay+Iy is stored in the lower word of Ay, while the upper word retains its original
value.
R8[Ix]
+2 (INC)
+0 (no update)
R4[Ax]
R5[Ax]
ALU
R9[Iy]
+2 (INC)
+0 (no update)
R6[Ay]
R7[Ay]
AU
Note: Three address processing methods:
1. Increment
2. Index register addition (Ix/Iy)
3. No increment
AU: Adder provided
for DSP addressing
Post-updating is used in all cases.
The address pointer can be decremented by setting −2/−4 in the index register.
Figure 2.12 X and Y Data Transfer Addressing
Single Data Addressing: DSP instructions include two single data transfer instructions
(MOVS.W, MOVS.L) that load data into, or store data from, a DSP register. With these
instructions, one of registers R2 to R5 is used as the single data transfer address register (As).
The following four kinds of addressing can be used with single data transfer instructions.
Rev. 5.0, 09/03, page 46 of 806