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1Muhammad Amir Yousaf
DIGITAL DESIGN WITH VHDLExercise 1
2Muhammad Amir Yousaf
What is VHDL?
What it is used for?
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VHDL vs Programming languages?
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VHDL
VERY HIGH SPEED INTEGRATED CIRCUIT HARDWARE DESCRIPTION LANGUAGE:
Origininally designed to describe and specify hardware.
Specifications were made executable with simulators.
Synthesizer were developed to synthesize.
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VHDL - MODULARITY
Component in VHDL is refferd as ’entity’ and has a clear interface.
Inputs
Outputs
Type and size.
Internal of component is called architecture declaration.Complexity is hidden inside.
Made of components and wires.
How the external world would see it.
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DESCRIPTION OF A DIGITAL COMPONENT.
A component is to be designed with following description:
A full adder that adds two 1 bit inputs and a carry-in bit. The result is shown at a 1 bit SUM and a carry-out bit.
Describe this component in (a standard descriptive language)
VHDLFull Adder
A
BCIN
SUM
COUT
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DESCRIPTION OF A FULLADDER WITH VHDL
Full Adder
A
BCIN
SUM
COUT
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DESCRIPTION OF A DIGITAL COMPONENT.
A component is to be designed with following description:
A full adder that adds two 1 bit inputs and a carry-in bit. The result is shown at a 1 bit SUM and a carry-out bit.
Describe this component in (a standard descriptive language)
VHDL
Full Adder
A
BCIN
SUM
COUT
Let add a ‘RESET’ pin in the component.
RST
9Muhammad Amir Yousaf
DESCRIPTION OF A DIGITAL COMPONENT.
VHDL code:
If RST = ’1’ then
SUM <= ‘0’;
COUT <= ‘0’;
else
-------
------
End if;
If is sequential, so must be contained in process.Sequential or procedural statements execute in the order as they appear in code.
label: process (<senstivity_list>)
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DESCRIPTION OF A FULLADDER
Full Adder
A
BCIN
SUM
COUT
RST
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EXERCISES
EX 1: Describe a system in VHDL with an input x and output y of type integer. The system gives x+10 at output whenever a change is detected on input.
EX 3: A MUX is described in VHDL as .
MUX
Make a 4-to-1 MUX using the structure of 2-to-1 MUXs.
EX 2: ´Describe a 4-bit comparator in VHDL using relational operators i.e > < =.
comp
4
4
x
y
gt
eqlt
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A MODEL OF A DIGITAL SYSTEM IS DESCRIBED
IS IT TIME TO TRANSLATE IT IN HARDWARE?
IS IT POOSIBLE TO SEE AND ANALYZE THE SYSTEM PERFORMANCE?
CAN WE SIMULATE THE RESULTS?
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SIMULATING DESCRIPTION OF DIGITAL DESIGN
A digital component is modeled in VHDL but not proven yet.
Model a ’TESTBENCH’ in VHDL to prove the performance of designed part.
’TESTBENCH’ applies stimulus to the design and simulates the response of system.
In stimulus we assign inputs to the system.
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TESTBENCH
Stimulus
TESTBENCH
Full Adder
A
BCIN
SUM
COUT
RST
Full AdderAB
CIN
SUM
COUT
RST
Display
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TESTBENCH BY XILINX
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TESTBENCH BY XILINX
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PRACTICAL
LET WE MODEL THIS IN VHDL WITH XILINX
START XILINX
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SYNTHESIZELET TRANSLATE OUR MODEL INTO HARDWARE
DIGILENT NEXYS2
User IOs8 slide switches.8 LEDs4 push buttons4 seven segment displays
Full Adder
A
BCIN
SUM
COUT
RST
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SYNTHESIZE
FPGA
User IOs8 slide switches.8 LEDs4 push buttons4 seven segment displays
.ucf file gives connection map
Top VHDL file
Gives top interface of the system.
Use Adept from Digilent to load the bit file in FPGA.
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Home Exercise:VGA:
Read about VGA controller to know that how it works.
VGA reference document and VHDL code is given at:
http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,400,789&Prod=NEXYS2
