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Section 3 DSP Operation
Rev. 4.00 Sep. 14, 2005 Page 115 of 982
REJ09B0023-0400
Table 3.9 Variation of PDMSB Operation
Mnemonic Function Source Source 2 Destination
PDMSB MSB detection Sx Dz
Sy Dz
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.
3.1.7 Rounding Operation
The DSP unit provides the rounding function that rounds from 32 bits to 16 bits. In case of
providing guard-bit parts, it rounds from 40 bits to 24 bits. When a round instruction is executed,
H'00008000 is added to the source operand data and then, the lower word is cleared. Figure 3.12
shows the rounding operation flow and figure 3.13 shows the operation definition. Table 3.10
shows the variation of this type of operation. The correspondence between each operand and
registers is the same as ALU fixed-point operations as shown in table 3.2.
As shown in figure 3.12, the rounding operation uses full-size data for both source and destination
operands. These operations are executed in the DSP stage as shown in figure 3.2. The DSP stage is
the same stage as the MA stage in which memory access is performed.
The rounding operation is always executed unconditionally, so that the DC, N, Z, V, and GT bits
in DSR are always updated in accordance with the operation result. The definition of the DC bit is
selected by the CS[2:0] (condition selection) bits in DSR. The result of these condition code bits is
the same as the ALU-fixed point arithmetic operations.