DSP56303 datasheet(69/292 Pages) FREESCALE

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Central Processor Unit (CPU) Registers

DSP56303 User’s Manual, Rev. 2

Freescale Semiconductor

4-11

5E1

Extension

Cleared if all the bits of the integer portion of the 56-bit result are all ones or all

zeros; otherwise, this bit is set. The Scaling mode defines the integer portion.

If the E bit is cleared, then the low-order fraction portion contains all the

significant bits; the high-order integer portion is sign extension. In this case,

the accumulator extension register can be ignored. If the E bit is set, it

indicates that the accumulator extension register is in use.

Scaling Mode

Integer Portion

No scaling

Bits 55–47

Scale down

Bits 55–48

Scale up

Bits 5–46

Reserved

Undefined

4U0

Unnormalized

Set if the two MSBs of the Most Significant Portion (MSP) of the result are

identical; otherwise, this bit is cleared. The MSP portion of the A or B

accumulators is defined by the Scaling mode.

Scaling Mode

Integer Portion

No scaling

U = (Bit 47 XOR Bit

46)

Scale down

U = (Bit 48 XOR Bit

47)

Scale up

U = (Bit 46 XOR Bit

45)

Reserved

U undefined

3N0

Negative

Set if the MSB of the result is set; otherwise, this bit is cleared.

2Z0

Zero

Set if the result equals zero; otherwise, this bit is cleared.

1V0

Overflow

Set if an arithmetic overflow occurs in the 56-bit result; otherwise, this bit is

cleared. V indicates that the result cannot be represented in the accumulator

arithmetic overflow occurs if the Data ALU result is not representable in the

accumulator without the extension part (that is, 48-bit accumulator or the

32-bit accumulator in Arithmetic Sixteen-bit mode).

0C0

Carry

Set if a carry is generated by the MSB resulting from an addition operation.

This bit is also set if a borrow is generated in a subtraction operation;

otherwise, this bit is cleared. The carry or borrow is generated from Bit 55 of

the result. The C bit is also affected by bit manipulation, rotate, and shift

instructions.

Table 4-2. Status Register Bit Definitions (Continued)

Bit Number

Bit Name

Reset Value

Description

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