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Section 3 DSP Operation
Rev. 4.00 Sep. 14, 2005 Page 103 of 982
REJ09B0023-0400
Signed Greater Than Mode: CS[2:0] = 100: The DC bit indicates whether or not the source 1
data (signed) is greater than the source 2 data (signed) as the result of compare operation PCMP.
So, a PCMP operation should be executed in advance when a conditional operation is executed
under this condition mode. This mode is similar to the Negative Value Mode described before,
because the result of a compare operation is usually a positive value if the source 1 data is greater
than the source 2 data. However, the signed bit of the result shows a negative value if the compare
operation yields a result beyond the range of the destination operand, including the guard-bit parts
(called "Over-range"), even though the source 1 data is greater than the source 2 data. The DC bit
is updated concerning this type of special case in this condition mode. The equation below shows
the definition of getting this condition:
DC = ~ {(Negative ^ Over-range) | Zero}
When the PCMP operation is executed under this condition mode, the result of the DC bit is the
same as the T bit's result of the CMP/GT operation of the SH core instruction.
Signed Greater Than or Equal Mode: CS[2:0] = 101: The DC bit indicates whether the source
1 data (signed) is greater than or equal to the source 2 data (signed) as the result of compare
operation PCMP. So, a PCMP operation should be executed in advance when a conditional
operation is executed under this condition mode. This mode is similar to the Signed Greater Than
Mode described before but the equal case is also included in this mode. The equation below shows
the definition of getting this condition:
DC = ~ (Negative ^ Over-range)
When the PCMP operation is executed under this condition mode, the result of the DC bit is the
same as the T bit's result of a CMP/GE operation of the SH core instruction.
The N bit always indicates the same state as the DC bit set in negative value mode by the CS[2:0]
bits. See the negative value mode part above. The Z bit always indicates the same state as the DC
bit set in zero value mode by the CS[2:0] bits. See the zero value mode part above. The V bit
always indicates the same state as the DC bit set in overflow mode by the CS[2:0] bits. See the
overflow mode part above. The GT bit always indicates the same state as the DC bit set in signed
greater than mode by the CS[2:0] bits. See the signed greater than mode part above.
Note: The DC bit is always updated as the carry flag for "PADDC" and is always updated as the
borrow flag for "PSUBC" regardless of the CS[2:0] state.
Overflow Protection: The S bit in SR is effective for any ALU fixed-point arithmetic operations
in the DSP unit. See section 3.1.8, Overflow Protection, for details.