Achronix Speedster22i User Macro Guide Manuale Utente Scaricare il pdf (Pagina 103)

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Chapter 5 – Arithmetic Functions

ALU

Two Input Adder / Subtractor with Programmable Load

ALU

a[1:0]

b[1:0]

d[1:0]

load

cin

s[1:0]

cout

Figure 5-1: Logic Symbol

ALU implements  eithe

r a two‐bit adder or two‐bit subtractor with adder/subtractor inputs

(a[1:0],b[1:0]),loadvalue(d[1:0]),LoadEnable(load)andcarry‐in(cin)inputs.Itgenerates

the sum/difference (s[1:0]) and carry‐out (cout) outputs.Asserting the load signal high

overridesthes[1:0]outputwiththevalueoftheLoa

dValued[1:0]input.MultipleALUblocks

may be combined by connecting the cout output of one slice to the cin input of the next

significanttwo‐bitslice.SelectionofwhethertheALUisconfiguredasanadderorsubtractor

isdeterminedbythevalueoftheinvert_bparameter.

Pins

Table 5-1: Pin Descriptions

Name Type Description

a[1:0]

Data Input a. D

ata Input a is a 2-bit two’s complement signed input,

where bit 1 is the most significant bit. In subtraction mode, Data Input a is

the minuend.

b[1:0]

Data Input b. D

ata Inputs b is a 2-bit two’s complement signed input,

where bit 1 is the most significant bit. In subtraction mode, Data Input b is

the subtrahend.

d[1:0]

Load Value input. I

nput d[1:0] is the value that is loaded onto the outputs

s[1:0] upon the active-high assertion of the load input.

load

Load input

(active-high). Asserting the load input high set the s[1:0] out-

put equal to the d[1:0] input.

cin

Carry In input(ac

tive-high). The cin is the carry-in to the ALU. Note that

for subtraction, cin should be tied high.

s[1:0]

Sum/Difference output.

If the invert_b parameter is set to 1’b0, the s[1:0]

output will reflect the sum of the a, b, and cin inputs if the load input is

low. If the invert_b parameter is set to 1’b1, the s[1:0] output will reflect

the difference of the a, b, cin inputs if the load input is low.

cout

Carry-out output. T

he cout is set high during an add when the s[1:0] out-

put overflows.

input

output

1 2 ... 98 99 100 101 102 103 104 105 106 107 108 ... 223 224

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