Altera Integer Arithmetic IP - Manual (Page 105)

Pre-adder
With pre-adder, additions or subtractions are done prior to feeding the multiplier.
There are five pre-adder modes:
• Simple mode
• Coefficient mode
• Input mode
• Square mode
• Constant mode
Note: When pre-adder is used (pre-adder coefficient/input/square mode), all data inputs to the multiplier
must have the same clock setting.
Pre-adder Simple Mode
In this mode, both operands derive from the input ports and pre-adder is not used or bypassed. This is the
default mode.
Figure 9-2: Pre-adder Simple Mode
a0
b0
Mult0
result
Pre-adder Coefficient Mode
In this mode, one multiplier operand derives from the pre-adder, and the other operand derives from the
internal coefficient storage. The coefficient storage allows up to 8 preset constants. The coefficient
selection signals are
coefsel[0..3]
.
The following settings are applied in this mode:
• The width of the
dataa[]
input (
WIDTH_A
) must be less than or equals to 25 bits
• The width of the
datab[]
input (
WIDTH_B
) must be less than or equals to 25 bits
• The width of the coefficient input must be less than or equals to 27 bits
This mode is expressed in the following equation.
The following shows the pre-adder coefficient mode of a multiplier.
9-4 Pre-adder
UG-01063
2014.12.19
Altera Corporation ALTMULT_ADD (Multiply-Adder)
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