l5 - 6.111 Lecture # 5 VHDL: Very High speed integrated...

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6.111 Lecture # 5 VHDL: Very High speed integrated circuit Description Language: All VHDL files have two sections: architecture and entity -- Massachusetts (Obsolete) Stoplight Example library ieee; use ieee.std_logic_1164.all; entity check is port(r, y, g: in std_logic; ok: out std_logic); end check; architecture logical of check is signal t1, t2, t3: std_logic; begin t1 <= r and (not g); t2 <= y and (not g); t3 <= (not r) and (not y) and g; ok <= t1 or t2 or t3; Entity section describes input and output Architecture section describes what to do with those signals end logical;
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library clause describes the basic library to make reference to use clause establishes definitions of many important items for most situations, use these 'as is' library ieee; use ieee.std_logic_1164.all; Other libraries will be used and you will have the opportunity to make libraries of your own.
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The entity declaration can be quite complex and has a lot of information I/O signals are referrred to as PORT s. These signals have Mode and Type The Mode of a signal can be in , out , buffer or inout in and out are straightforward buffer is like out , but is available within the architecture inout is a tri-state (bidirectional) Note how vectors (multi-bit) signals are handled.
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We can avoid using Mode BUFFER Note the additional declaration of signal inside the architecture section. Note the names in the architecture section need not be unique and are there for readability
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LIBRARY ieee; use ieee.std_logic_1164.all; (VHDL is defined by IEEE Standard 1164) std_logic types can take values: U Uninitialized X Unknown 0 Zero 1 One Z Tristate (Must be upper case!) W
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l5 - 6.111 Lecture # 5 VHDL: Very High speed integrated...

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