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Introduction to VHDL History of VHDL Naming Conventions Libraries and packages Entities Entity Declaration Entity Example Ports Architectures Architecture declaration Architecture example Configurations Signals Signal representation Multivalued logic representation Built in data types Synthesis vs simulation Logical operators Assignment statements Process statements D Flip flop example code Finite state machine(FSM) Finite state machine example Combinational circuit example code Quad 2 input MUX example Seven segment display controller 8 Bit register 32 bit counter
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MVL (Multi-Valued Logic) representations provide the additional values necessary to represent high-impedance and unknown signals
• Two popular multi-valued signal representations are defined by ieee.std_logic_1164:
œ MVL - 4
œ MVL - 9 MVL - 4 adds 2 values (”X‘ and ”Z‘) to model the state of signals more accurately:
• Wires can be driven with multiple values
• MVL-4 is rarely used since it still does not provide enough states to model signals accurately MVL - 9 adds 5 more values to model the state of signals very accurately:
been driven Four standardized types use MVL-9:
Unresolved Types
std_ulogic
std_ulogic_vector( <max> DOWNTO <min>)
Resolved Types
std_logic
std_logic_vector( <max> DOWNTO <min> )
• Resolved types use resolution functions to determine the value on a signal when conflicting values are driven on the signal at the same time
resolved when conflicting values have been
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