dsp56800e Freescale Semiconductor, Inc, dsp56800e Datasheet - Page 247

• Manufacturer Part Number: dsp56800e
• Description: 16-bit Digital Signal Controller Core
• Manufacturer: Freescale Semiconductor, Inc

A description of each of the bits in the status register appears in the following subsections. The
descriptions that are given for the CCR bits are the standard definitions, but these bits may be set or cleared
slightly differently depending on the instruction that is being executed. More information on the condition
code bits is found in Section 5.7, “Condition Code Calculation,” on page 5-38 and in Appendix B,
“Condition Code Calculation.”
8.2.2.1
The carry (C) bit is used to reflect a variety of conditions. It is set under the following circumstances:
When not set under one of these conditions, this bit is always cleared.
8.2.2.2
The overflow (V) bit is set if the result of an arithmetic operation overflows (is too large to fit in) the size
of the specified destination. If overflow does not occur, this bit is always cleared.
8.2.2.3
The zero (Z) bit is set if the result of an operation is equal to zero. If the result is non-zero, this bit is
cleared.
8.2.2.4
The negative (N) bit is set if the result of an operation is negative. A value is considered negative if the
MSB is set; otherwise it is considered positive. If the MSB of the result is not set, this bit is cleared.
8.2.2.5
The unnormalized (U) bit is set if the value resulting from an operation is not normalized. A value is
considered normalized if all bits to the right of the binary point are significant. For an accumulator result,
this condition means that bits 31 and 30 of the result should be different. Thus, the U bit is computed as
follows:
Normalized values have the property that, for a positive number p, the relation 0.5 < p < 1.0 is satisfied; for
a negative value n, the relation is –1.0 < n < –0.5.
This bit is not affected by the OMR’s CM bit.
Freescale Semiconductor
•
•
•
•
If an addition operation results in a carry out of the MSB of the result
If a borrow was necessary when a subtraction operation was performed
When all bits specified by the mask are set (or cleared, depending on the instruction) in their
corresponding operand for bit-manipulation instructions
When the last bit that is to be shifted or rotated out of the MSB or LSB of an operand in a shift or
rotate operation is a one
U = (Bit 31 ⊕ Bit 30)
Carry (C)—Bit 0
Overflow (V)—Bit 1
Zero (Z)—Bit 2
Negative (N)—Bit 3
Unnormalized (U)—Bit 4
When individual bits in the SR are modified, the BFCLR, BFCHG, or
BFSET instructions should be used instead of a MOVE instruction to
prevent the accidental modification of other bits.
Program Controller
NOTE:
Program Controller Programming Model
8-9