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Section 3 DSP Operation
Rev. 4.00 Sep. 14, 2005 Page 102 of 982
REJ09B0023-0400
Negative Value Mode: CS[2:0] = 001: The DC flag indicates the same state as the MSB of the
operation result. When the result is a negative number, the DC bit shows 1. When it is a positive
number, the DC bit shows 0. The ALU always executes 40-bit arithmetic operation, so the sign bit
to detect whether positive or negative is always got from the MSB of the operation result
regardless of the destination operand. Some examples are shown in figure 3.4.
Example 1
Sign bit
Guard bits
Negative value
1100
0000
+)
0000
0000
0000
0000
0000
0000
0000
0000
0000
0001
1100 0000 0000 0000 0000 0001
Example 2
Sign bit
Guard bits
Positive value
0011
0000
+)
0000
0000
0000
1000
0000
0000
0000
0000
0000
0001
0011 0000 1000 0000 0000 0001
Figure 3.4 DC Bit Generation Examples in Negative Value Mode
Zero Value Mode: CS[2:0] = 010: The DC flag indicates whether the operation result is 0 or not.
When the result is 0, the DC bit shows 1. When it is not 0, the DC bit shows 0.
Overflow Mode: CS[2:0] = 011: The DC bit indicates whether or not overflow occurs in the
result. When an operation yields a result beyond the range of the destination register, except the
guard-bit parts, the DC bit is set. Even though guard bits are provided, the DC bit always indicates
the result of when no guard bits are provided. So, the DC bit is always set if the guard-bit parts are
used for large number representation. Some DC bit generation examples in overflow mode are
shown in figure 3.5.
Example 1
Overflow detecting field
Guard bits
Overflow case
1111
1111
+)
1111
1111
1111
1000
1111
0000
1111
0000
1111
0000
1111 1111 0111 1111 1111 1111
Example 2
Overflow detecting field
Guard bits
Non overflow case
1111
1111
+)
1111
1111
1111
1000
1111
0000
1111
0000
1111
0001
1111 1111 1000 0000 0000 0000
Figure 3.5 DC Bit Generation Examples in Overflow Mode
Summary of Contents for HD6417641
Page 2: ...Rev 4 00 Sep 14 2005 Page ii of l...
Page 7: ...Rev 4 00 Sep 14 2005 Page vii of l...
Page 11: ...Rev 4 00 Sep 14 2005 Page xi of l USB Universal serial bus WDT Watch dog timer...
Page 12: ...Rev 4 00 Sep 14 2005 Page xii of l...
Page 28: ...Rev 4 00 Sep 14 2005 Page xxviii of l...
Page 204: ...Section 4 Clock Pulse Generator CPG Rev 4 00 Sep 14 2005 Page 154 of 982 REJ09B0023 0400...
Page 212: ...Section 5 Watchdog Timer WDT Rev 4 00 Sep 14 2005 Page 162 of 982 REJ09B0023 0400...
Page 228: ...Section 6 Power Down Modes Rev 4 00 Sep 14 2005 Page 178 of 982 REJ09B0023 0400...
Page 246: ...Section 8 X Y Memory Rev 4 00 Sep 14 2005 Page 196 of 982 REJ09B0023 0400...
Page 318: ...Section 11 User Break Controller UBC Rev 4 00 Sep 14 2005 Page 268 of 982 REJ09B0023 0400...
Page 454: ...Section 12 Bus State Controller BSC Rev 4 00 Sep 14 2005 Page 404 of 982 REJ09B0023 0400...
Page 504: ...Section 14 U Memory Rev 4 00 Sep 14 2005 Page 454 of 982 REJ09B0023 0400...
Page 566: ...Section 17 Compare Match Timer CMT Rev 4 00 Sep 14 2005 Page 516 of 982 REJ09B0023 0400...
Page 868: ...Section 21 A D Converter Rev 4 00 Sep 14 2005 Page 818 of 982 REJ09B0023 0400...
Page 914: ...Section 23 I O Ports Rev 4 00 Sep 14 2005 Page 864 of 982 REJ09B0023 0400...
Page 956: ...Section 24 List of Registers Rev 4 00 Sep 14 2005 Page 906 of 982 REJ09B0023 0400...
Page 1016: ...Section 25 Electrical Characteristics Rev 4 00 Sep 14 2005 Page 966 of 982 REJ09B0023 0400...
Page 1024: ...Appendix Rev 4 00 Sep 14 2005 Page 974 of 982 REJ09B0023 0400...
Page 1032: ...Rev 4 00 Sep 14 2005 Page 982 of 982 REJ09B0023 0400 X X Y data addressing 52 X Y memory 193...
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