SH7721 datasheet(169/1524 Pages) RENESAS

169 / 1524 page

Section 3 DSP Operating Unit

Rev. 3.00 Jan. 18, 2008 Page 107 of 1458

REJ09B0033-0300

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Addressing Mode for Double Data Transfer Instructions

The double data transfer instructions supports the following three addressing modes.

• Non-update address register addressing

The Ax and Ay registers are address pointers. They are not updated.

• Increment address register addressing

The Ax and Ay registers are address pointers. After a data transfer, they are each incremented

by 2 (post-increment).

• Addition index register addressing

The Ax and Ay registers are address pointers. After a data transfer, the value of the Ix or Iy

supports decrement addressing mode. To perform decrement, –2 or –4 is set in the index

When using X/Y data addressing, bit 0 of the address pointer is invalid; bits 0 and 1 of the address

pointer are invalid in word access. Accordingly, bit 0 of the address pointer and index register

must be cleared to 0 in X/Y data addressing.

When accessing X and Y memory using the X and Y buses, the upper word of Ax and Ay 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. The Ax and Ax +Ix operations are executed in longword (32 bits) and the

upper word may be changed according to the result.

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Single Data Addressing

The following four kinds of addressing can be used with single data transfer instructions.

• Non-update address register addressing

The As register is an address pointer. An access to @As is performed but As is not updated.

• Increment address register addressing:

The As register is an address pointer. After an access to @As, the As register is incremented

by 2 or 4 (post-increment).

• Addition index register addressing:

The As register is an address pointer. After an access to @As, the value of the Is register is

added to the As register (post-increment).

• Decrement address register addressing:

The As register is an address pointer. Before a data transfer, –2 or –4 is added to the As

SH7721 Datasheet(PDF) 169 Page - Renesas Technology Corp