Xilinx 7 Series User Manual page 35

ALUMODE Inputs
The 4-bit ALUMODE controls the behavior of the second stage add/sub/logic unit.
ALUMODE = 0000 selects add operations of the form Z + (X + Y + CIN). CIN is the
output of the CARRYIN mux (see
operations of the form Z – (X + Y + CIN). ALUMODE = 0001 can implement
–Z + (X + Y + CIN) – 1. ALUMODE = 0010 can implement –(Z + X + Y + CIN) – 1, which
is equivalent to not (Z + X + Y + CIN). The negative of a two's complement number is
obtained by performing a bitwise inversion and adding one, for example, –k = not (k) + 1.
Other subtract and logic operations can also be implemented with the enhanced
add/sub/logic unit. See
Table 2-10: Three-Input ALUMODE Operations
Z + X + Y + CIN
Z – (X + Y + CIN)
–Z + (X + Y + CIN) – 1 =
not (Z) + X + Y + CIN
not (Z + X + Y + CIN) =
–Z – X – Y – CIN - 1
Notes:
1. In two's complement: –Z = not (Z) + 1
See
7 Series DSP48E1 User Guide
UG479 (v1.10) March 27, 2018
Table
DSP Operation
Table 2-13, page 42 for two-input ALUMODE operations and
www.xilinx.com
Simplified DSP48E1 Slice Operation
Figure 2-11). ALUMODE = 0011 selects subtract
2-10.
OPMODE[6:0]
Any legal OPMODE
Any legal OPMODE
Any legal OPMODE
Any legal OPMODE
ALUMODE[3:0]
3 2 1 0
0 0 0 0
0 0 1 1
0 0 0 1
0 0 1 0
Figure A-3, page 56.
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