Achronix Speedster22i User Macro Guide Manuale Utente Scaricare il pdf (Pagina 104)

Arithmetic Functions ALU

Speedster Macro Cell Library

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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tw

o’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

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Achronix Speedster22i User Macro Guide Manuale Utente Pagina 104