Texas Instruments TMS320C28x Reference Manual page 49

Condition Operation Performed by SAT ACC Instruction
OVC = 0
Leave ACC and OVC unchanged.
OVC > 0
Saturate ACC in the positive direction (fill ACC with 7FFF FFFF
OVC < 0
Saturate ACC in the negative direction (fill ACC with 8000 0000
PM Product shift mode bits. This 3-bit value determines the shift mode for any output opera-
tion from the product (P) register. The shift modes are shown in the following table. The out-
Bits 9−7
put can be to the ALU or to memory. All instructions that are affected by the product shift
mode will sign extend the P register value during a right shift operation. At reset, PM is
cleared (left shift by 1 bit is the default).
PM is summarized as follows:
000
001
010
011
100
101
110
111
Note: For performing unsigned arithmetic, you must use a product shift of 0 (PM = 001) to avoid sign extension and genera-
tion of incorrect results.
Table 2−4. Instructions That Affect OVC/OVCU (Continued)
Signed Addition Instructions
MOVU OVC,loc16
Left shift by 1. During the shift, the low-order bit is zero filled. At reset, this mode
is selected.
No shift
Right shift by 1. During the shift, the lower bits are lost, and the shifted value is sign
extended.
Right shift by 2. During the shift, the lower bits are lost, and the shifted value is sign
extended.
Right shift by 3. During the shift, the lower bits are lost, and the shifted value is sign
extended.
Right shift by 4. During the shift, the lower bits are lost, and the shifted value is sign
extended.
Note, if AMODE = 1, then 101 is a left shift by 4.
Right shift by 5. During the shift, the lower bits are lost, and the shifted value is sign
extended.
Right shift by 6. During the shift, the lower bits are lost, and the shifted value is sign
extended.
Table 2−5 lists instructions that are affected by the PM bits. See the instruction
set in chapter 6 for a complete description of each instruction.
Status Register (ST0)
Effect on OVC/OVCU
OVC = [loc16(5:0)]
), and clear OVC.
16
), and clear OVC.
16
Central Processing Unit 2-19