Implementing a Comparison Function Using EABs

This example uses two FLEX 10K EABs to implement a comparison function. The top-level file is named eab_comp.gdf. Two lower-level files named eabcomp.tdf, which were created in the Altera Hardware Description Language (AHDL), perform a comparison on two 5-bit buses. A third lower-level file named final_comp.tdf performs the final comparison. The outputs are 00 if a equals b, 01 if a is greater than b, and 10 is a is less than b.

You must assign a logic option to the two eabcomp.tdf files in order to implement them in the EAB. To implement the assignment:

1. Select both eabcomp symbols in the Graphic Editor and choose Logic Options (Assign menu). The Logic Options dialog box will appear.
2. Choose the Individual Logic Options button.
3. In the Individual Logic Options dialog box, turn on Implement in EAB.
4. Choose OK twice.

Download the Graphic Editor file used in this example:

• Download eab_comp.gdf

The use of this design is governed by, and subject to, the terms and conditions of the Altera Hardware Reference Design License Agreement.

eabcomp.tdf

constant AeqB  = b"00";
constant AgreB = b"01";
constant BgreA = b"10";


SUBDESIGN eabcomp
(
    a[4..0], b[4..0], clock : INPUT;
    comp[1..0] : OUTPUT;
)

VARIABLE
a_ff[4..0], b_ff[4..0] : dff;  -- Flipflops used for registering 
                               -- inputs and outputs

BEGIN
a_ff[].clk = clock;
b_ff[].clk = clock;
a_ff[].d = a[];
b_ff[].d = b[];

    If a_ff[].q == b_ff[].q then
    comp[] = AeqB;
    elsif a_ff[].q > b_ff[].q then
    comp[] = AgreB;
    elsif a_ff[].q < b_ff[].q then
    comp[] = BgreA;
    END IF;
END;

final_comp.tdf

constant AeqB  = b"00";

SUBDESIGN final_comp
(
    msbits[1..0], lsbits[1..0], clock   : INPUT;
    comp[1..0] : OUTPUT;
)

VARIABLE
 comp[1..0]  : dff;

BEGIN
comp[].clk = clock;
    If msbits[] == AeqB then
    comp[].d = lsbits[];
    else 
    comp[].d = msbits[];
    END IF;
END;

For more information on using this example in your project, go to:

• How to Use Graphic Editor Examples
• How to Use AHDL Examples
• MAX+PLUS II Help

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