Computer Organization VonNeuman VHDL Arrays

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Computer Organization (Von-Neuman)VHDL (Arrays)
Arrays are a collection of values of the same
type. The position within the array is given by a
scalar value called its index. type WORD is
array (0 to 31) of bit -- index from 0 to
31 type WORD is array (31 downto 0) of bit --
index values start at 31 type CONTROLLER_STATE
is (initial, idle,active, error) -- index not a
value
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Computer Organization (Von-Neuman)VHDL (Memory
Example)
entity memory is port (ADDRESS in bit_vector(0
to 3) DATA out bit_vector(0 to 7) end
memory library vector use vector.functions.all
architecture beh of mem is begin memprocess
process (ADDRESS) is subtype byteword is
bit_vector (0 to 7) type mem_add is array (0 to
8) of byteword variable index mem_add
(xff, xff, xff, xff, xff, xff, xff,
xff) begin DATA lt index (to_natural
(ADDRESS)) end process end beh

Entity Memory
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Address
Arch Memory
8
0000 0001 0010 0011 0100 0101 0110 0111 1000
Data
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Computer Organization (Von-Neuman)VHDL (Block
Statement)

• Block Statement (p188 Bhasker)
• Statements between are optional
• Disables signal drivers by using guards.
• To limit the scope of declarations, including
  signal.
• To represent a portion design.
• Declarations within block end block are visible
  only within block.
• If a guard-expression appears in the block
  statement, it means that any statement that is
  guarded (B), will be assigned to the target
  signal(A) when the guard-expression is true (Alt
  guarded B)
• SYNTAX
• block-label block(guard-expression) is
• block-header
• block-declarations
• begin
• concurrent-statements
• end block block-label
• GATED INVERTER EXAMPLE
• B1 block (STROBE 1)
• begin
• Z lt guarded not A
• end block B1

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VHDL Assert

• Syntax.. assert boolean-expression
• report string-expression
• severity expression
• If the value of the Boolean expression is false,
  the report message is printed along with the
  severity level.