SH7721 datasheet(150/1524 Pages) RENESAS

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Section 3 DSP Operating Unit

Rev. 3.00 Jan. 18, 2008 Page 88 of 1458

REJ09B0033-0300

Before entering the exception handling state, all bits including the DSP extension bits of the SR

registers are saved in the SSR. Before returning from the exception handling, all bits including the

DSP extension bits of the SR must be restored. If the repeat control must be recovered before

entering the exception handling state, the RS and RE registers must be recovered to the value that

existed before exception handling. In addition, if it is necessary to recover modulo control before

entering the exception handling state, the MOD register must be recovered to the value that

existed before exception handling.

3.2.4

DSP Registers

The DSP unit incorporates eight data registers (A0, A1, X0, X1, Y0, Y1, M0, and M1) and a status

with the exception of registers A0 and A1. Registers A0 and A1 include 8 guard bits (fields A0G

and A1G), giving them a total width of 40 bits. The DSR register stores the DSP data operation

result (zero, negative, others). The DSP register has a DC bit whose function is similar to the T bit

in the CPU register. For details on DSR bits, refer to section 3.5, DSP Data Operation Instructions.

A0G

A1G

................

CS[2:0]

(a) DSP data registers

(b) DSP status register (DSR)

32 31

765

Initial value

DSR : All 0

Others: Undefined

Figure 3.3 DSP Register Configuration

SH7721 Datasheet(PDF) 150 Page - Renesas Technology Corp