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Section 3 DSP Operation
Rev. 4.00 Sep. 14, 2005 Page 117 of 982
REJ09B0023-0400
3.1.8 Overflow
Protection
The S bit in SR is effective for any arithmetic operations executed in the DSP unit, including the
SH's standard multiply and MAC operations. The S bit in SR, in SH's CPU core, is used as the
overflow protection enable bit. The arithmetic operation overflows when the operation result
exceeds the range of two's complement representation without guard-bit parts. Table 3.11 shows
the definition of overflow protection for fixed-point arithmetic operations, including fixed-point
signed by signed multiplication described in section 3.1.4, Fixed-Point Multiply Operation. Table
3.12 shows the definition of overflow protection for integer arithmetic operations. When an SH's
standard multiply or MAC operation is executed, the S bit function is completely the same as the
current SH CPU's definition.
When the overflow protection is effective, overflow never occurs. So, the V bit is cleared, and the
DC bit is also cleared when the overflow mode is selected by the CS[2:0] bits.
Table 3.11 Definition of Overflow Protection for Fixed-Point Arithmetic Operations
Sign Overflow
Condition
Fixed Value
Hex Representation
Positive
Result > 1 – 2
–31
1 – 2
–31
00 7FFF FFFF
Negative
Result < –1
–1
FF 8000 0000
Table 3.12 Definition of Overflow Protection for Integer Arithmetic Operations
Sign Overflow
Condition
Fixed Value
Hex Representation
Positive
Result > 2
15
– 1
2
15
– 1
00 7FFF
****
Negative
Result < –2
15
–2
15
FF
8000
****
Note:
*
means Don't care.
Содержание HD6417641
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Страница 454: ...Section 12 Bus State Controller BSC Rev 4 00 Sep 14 2005 Page 404 of 982 REJ09B0023 0400...
Страница 500: ...Section 13 Direct Memory Access Controller DMAC Rev 4 00 Sep 14 2005 Page 450 of 982 REJ09B0023 0400...
Страница 504: ...Section 14 U Memory Rev 4 00 Sep 14 2005 Page 454 of 982 REJ09B0023 0400...
Страница 566: ...Section 17 Compare Match Timer CMT Rev 4 00 Sep 14 2005 Page 516 of 982 REJ09B0023 0400...
Страница 734: ...Section 18 Multi Function Timer Pulse Unit MTU Rev 4 00 Sep 14 2005 Page 684 of 982 REJ09B0023 0400...
Страница 868: ...Section 21 A D Converter Rev 4 00 Sep 14 2005 Page 818 of 982 REJ09B0023 0400...
Страница 914: ...Section 23 I O Ports Rev 4 00 Sep 14 2005 Page 864 of 982 REJ09B0023 0400...
Страница 956: ...Section 24 List of Registers Rev 4 00 Sep 14 2005 Page 906 of 982 REJ09B0023 0400...
Страница 1016: ...Section 25 Electrical Characteristics Rev 4 00 Sep 14 2005 Page 966 of 982 REJ09B0023 0400...
Страница 1024: ...Appendix Rev 4 00 Sep 14 2005 Page 974 of 982 REJ09B0023 0400...
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