HD6417320 RENESAS [Renesas Technology Corp], HD6417320 Datasheet - Page 191

• Manufacturer Part Number: HD6417320
• Description: Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7700 Series
• Manufacturer: RENESAS [Renesas Technology Corp]

(2)
The DC flag indicates the same value as the MSB of the operation result. When the result is a
negative number, the DC bit shows 1. When it is 0 or 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 3.12.
(3)
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.
(4)
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 in the destination register, the DC bit always indicates the
result of when no guard bits are provided. So, the DC bit is always set to 1 if the guard-bit parts
are used for large number representation. Some DC bit generation examples in overflow mode are
shown in figure 3.13.
Negative Value Mode: CS[2:0] = B'001
Zero Value Mode: CS[2:0] = B'010
Overflow Mode: CS[2:0] = B'011
Figure 3.12 DC Bit Generation Examples in Negative Value Mode
+)
+)
Figure 3.13 DC Bit Generation Examples in Overflow Mode
1111
1111
111111110111111111111111
Guard bits
Guard bits
1100
0000
1100 0000 0000 0000 0000 0001
1111
1111
0000
0000
Sign bit
Overflow case
Negative value
Example 1
Example 1
1111
1000
Overflow detecting field
0000
0000
1111
0000
0000
0000
1111
0000
0000
0000
1111
0000
0000
0001
+)
+)
Guard bits
1111
1111
111111111000 0000 0000 0000
Guard bits
0011
0000
0011 0000 1000 0000 0000 0001
1111
1111
0000
0000
Non overflow case
Rev. 3.00 Jan. 18, 2008 Page 129 of 1458
Sign bit
Positive value
Example 2
Example 2
1111
1000
0000
1000
Overflow detecting field
1111
0000
0000
0000
Section 3 DSP Operating Unit
1111
0000
0000
0000
1111
0001
0000
0001
REJ09B0033-0300