Data Flow Modeling in VHDL: A Comprehensive Guide for FPGA and ASIC Design, Slides of Digital Systems Design

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Data Flow Modelingin VHDL

VHDL Descriptions^ structuraldataflow Components and Concurrentinterconnectsstatements

-^ Testbenches behavioral(sequential) Sequential statements • Registers • State machines • Instruction decoders Subset most suitable for synthesis

Types of VHDL Description

Register Transfer Level (RTL) Design Description^ Combinational

Logic^

CombinationalLogic

Registers

…

Today ’ s Topic

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Data-Flow VHDL • simple concurrent signal assignment( 

)

-^ conditional concurrent signal assignment

(when-else)

-^ selected concurrent signal assignment

(with-select-when)

-^ generate scheme for equations Concurrent Statements (for-generate)

Wires and Buses ECE 448 – FPGA and ASIC Design with VHDL

SignalsSIGNAL a : STD_LOGIC;SIGNAL b : STD_LOGIC_VECTOR(7 DOWNTO 0);

a 1 wire b 8 bus

Splitting buses^ SIGNAL^ a:^ STD_LOGIC_VECTOR(

DOWNTO^ 0);

SIGNAL^ b:^ STD_LOGIC_VECTOR(

DOWNTO^ 0);

SIGNAL^ c:^ STD_LOGIC;SIGNAL^ d:^ STD_LOGIC_VECTOR(

DOWNTO^ 0);

a^ <=^ d(9^ downto^ 6);b^ <=^ d(5^ downto^ 1);c^ <=^ d(0);

a 410 db 5 c

Data-flow VHDL: Example^ x y cin

s cout docsity.com

Data-flow VHDL: Example (2) ARCHITECTURE dataflow OF fulladd ISBEGINs <=^ x XOR y XOR cin ;cout <= (x AND y) OR (cin AND x) OR (cin AND y) ;END dataflow ;

Logic Operators• Logic operators^ and^ or^ • Logic operators precedence

nand^ nor^ xor^

not^ xnor not and^ or^ nand^ nor^ xor^ xnor Highest Lowest

only in VHDL-93or later docsity.com

RTL Hardware Design^

Chapter 4^

16

arith_result <= a + b + c – 1;

RTL Hardware Design^

Chapter 4^

17

Signal assignment statement with aclosed feedback loop• a signal appears in both sides of aconcurrent assignment statement• E.g.,^ q^ <= (( not q )^

and^ ( not^ en))^ or

(d^ and^ en);

• Syntactically correct• Form a closed feedback loop• Should be avoided

Conditional concurrent signal assignment^ target_signal <=^ value1^ when^ condition

else value2^ when^ condition

else

.^.^. valueN-1^ when^ conditionN-

else valueN ; When - Else

Most often implied structure^ target_signal

<=^ value1^ when^ condition

else value2^ when^ condition

else

.^.^. valueN-1^ when^ conditionN-

else valueN ; When - Else Value N^ .…Value N-1 Condition N- Value 2Value 1Condition 2Condition 1

Target Signal

…^

0011 0 1