SH7710 Datasheet, PDF (163/996 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7700 Series

Section 3 DSP Operating Unit
Example 1
Guard bits
0000 0000 1111111111111111
+) 0000 0000 0000 0000 0000 0001
0000 0001 0000 0000 0000 0000
Carry detecting point
Carry is detected
Example 2
Guard bits
111111110111 0000 0000 0000
+) 0011 11110001 0000 0000 0000
(1)0011 11101000 0000 0000 0000
Carry detecting point
Carry is not detected
Example 3
Guard bits
0000 0000 0000 0000 0000 0001
–) 0000 0000 0000 0000 0000 0001
0000 0000 0000 0000 0000 0000
Borrow detecting point
Borrow is not detected
Example 4
Guard bits
0000 0000 0001 0000 0000 0001
–) 0000 0000 0001 0000 0000 0010
111111111111111111111111
Borrow detecting point
Borrow is detected
Figure 3.11 DC Bit Generation Examples in Carry or Borrow Mode
Negative Value Mode: CS[2:0] = 001: 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 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.
Example 1
Guard bits
1100 0000 0000 0000 0000 0000
+) 0000 0000 0000 0000 0000 0001
1100 0000 0000 0000 0000 0001
Sign bit
Negative value
Example 2
Guard bits
0011 0000 0000 0000 0000 0000
+) 0000 0000 1000 0000 0000 0001
0011 0000 1000 0000 0000 0001
Sign bit
Positive value
Figure 3.12 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
Rev. 2.00 Dec. 07, 2005 Page 121 of 950
REJ09B0079-0200