Achronix Speedster22i User Macro Guide - Manual (Page 104)

Arithmetic Functions ALU
Speedster Macro Cell Library www.achronix.com PAGE 87
Parameters
Table 5-2: Parameters
Parameter Defined Values Default Value
invert_b 1’b0
invert_b
The invert_b parameter defines if the ALU functions as an adder or a subtractor. Setting the
invert_b parameter to 1’b0 configures the ALU to perform two’s complement addition of a[1:0]
+ b[1:0] + cin. Setting the invert_b parameter to 1’b1 configures the ALU to invert the b[1:0]
input so that the two’s complement subtraction of a[1:0] ‐ b[1:0] is performed. Note that when
subtractions is desired, the cin input must be tied high. When multiple ALUs are connected to
perform higher resolution subtractors, only the cin of the LSB of the subtractor is to be tied
high.
Table 5-3: Function Table When invert_b = 1’b0.
load cin s[1:0] Note
1 X d[1:0] Load
0 - a[1:0] + b[1:0] + cin Add
Table 5-4: Function Table When invert_b = 1’b1.
load cin s[1:0] Note
1 X d[1:0] Load
0 1 a[1:0] - b[1:0] Subtract
0 0 a[1:0] - b[1:0] - 1 Subtract - 1
Verilog Instantiation Template
ALU #(.invert_b(1’b0))
instance_name(.a(user_a),
.b(user_b),
.d(user_load_value),
.load(user_load),
.cin(user_carry_in),
.s(user_sum),
.cout(user_cout));
1’b0, 1’b1