SH7720 Datasheet, PDF (190/1524 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7700 Series

Section 3 DSP Operating Unit
(1) Carry or Borrow Mode: CS[2:0] = B'000
The DC bit indicates that carry or borrow is generated from the most significant bit of the
operation result, except the guard-bit parts. Some examples are shown in figure 3.11. This mode is
the default condition. When the input data is negative in a PABS or PNEG instruction, carry is
generated.
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
Rev. 3.00 Jan. 18, 2008 Page 128 of 1458
REJ09B0033-0300