SH7721 datasheet(148/1524 Pages) RENESAS

148 / 1524 page

Section 3 DSP Operating Unit

Rev. 3.00 Jan. 18, 2008 Page 86 of 1458

REJ09B0033-0300

(2)

Repeat Start Register (RS)

The repeat start register (RS) holds the start address of a loop repeat module that is controlled by

the repeat function. This register can be accessed in DSP mode. At reset, the initial value of this

(3)

Repeat End Register (RE)

The repeat end register (RE) holds the end address of a loop repeat module that is controlled by

the repeat function. This register can be accessed in DSP mode. At reset, this register is initialized

to 0. This register is not affected in the exception handling state.

(4)

Modulo Register (MOD)

The modulo register stores the modulo end address and modulo start address for modulo

addressing in upper and lower 16 bits. The upper and lower 16 bits of the modulo register are

referred to as the ME register and MS register, respectively. This register can be accessed in DSP

mode. At reset, the initial value of this register is undefined. This register is not affected in the

exception handling state.

The above registers can be accessed by the control register load instruction (LDC) and store

instruction (STC). Note that the LDC and STC instructions for the RS, RE, and MOD registers can

be used only in privileged DSP mode and user DSP mode. The LDC and STC instruction for the

SR register can be executed only when the MD bit is set to 1 or in user DSP mode. Note, however,

that the LDC and STC instructions can modify only the RC11 to RC0, RF1 to RF0, DMX, and

DMY bits in the SR, as described below.

• In user mode, if the LCD and STC instructions are used for the RS, an illegal instruction

exception occurs.

• In privileged and privileged DSP modes, all SR bits can be modified.

• In user DSP mode, the SR can be read by the STC instruction.

• In user DSP mode, the LDC instruction can be issued to the SR but only the DSP extension

bits can be modified.

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