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Lecture #7 Agenda VHDL Data Types Announcements n/a

ECE 4110– Sequential Logic Design. Lecture #7 Agenda VHDL Data Types Announcements n/a. Data Types.

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Lecture #7 Agenda VHDL Data Types Announcements n/a

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  1. ECE 4110– Sequential Logic Design Lecture #7 • Agenda • VHDL Data Types • Announcements • n/a

  2. Data Types • Signals- a single bit is considered a Scalar quantity- a bus (or multiple bits represented with one name) is called a Vector- in VHDL, we can define a signal bus as: data_bus : in bit_vector (7 downto 0); -- we will use "downto" or data_bus : in bit_vector (0 to 7);- the Most Significant Bit (MSB) is ALWAYS on the left of the range description: ex) data_bus : in bit_vector (7 downto 0); data_bus(7) = MSB ex) data_bus : in bit_vector (0 to 7); data_bus(0) = MSB

  3. Data Types • Signals- there are "Internal" and "External" signalsInternal - are within the Entity's InterfaceExternal - are outside the Entity's Interface and connect it to other systems

  4. Data Types • Scalar Data Types (Built into VHDL)- scalar means that the type only has one value at any given time Boolean - values {TRUE, FALSE} - not the same as '0' or '1'Character - values are all symbols in the 8-bit ISO8859-1 set (i.e., Latin-1) - examples are '0', '+', 'A', 'a', '\'Integer - values are whole numbers from -2,147,483,647 to +2,147,483,647 - the range comes from +/- 232 - examples are -12, 0, 1002 Real - values are fractional numbers from -1.0E308 to +1.0E308 - examples are 0.0, 1.134, 1.0E5 Bit - values {'0', '1'} - different from Boolean - this type can be used for logic gates - single bits are always represented with single quotes (i.e., '0', '1')

  5. Data Types • Array Data Types (Built into VHDL)- array is a name that represents multiple signalsBit_Vector - vector of bits, values {'0', '1'} - array values are represented with double quotes (i.e., "0010") - this type can be used for logic gates ex) Addr_bus : in BIT_VECTOR (7 downto 0); - unlimited range - first element of array has index=0 (i.e., Addr_bus(0)…) String - vector of characters, values{Latin-1} - again use double quotes - define using "to" or "downto" ("to" is easier for strings) ex) Message : string (1 to 10) := "message here…" - first element in array has index=1, this is different from BIT_VECTOR

  6. Data Types • Physical Data Types (Built into VHDL)- these types contain object value and units- NOT synthesizableTime - range from -2,147,483,647 to +2,147,483,647 - units: fs, ps, ns, us, ms, sec, min, hr • User-Defined Enumerated Types- we can create our own descriptive types, useful for State Machine- no quotes neededex) type States is (Red, Yellow, Green);

  7. STD_LOGIC Data Types • STD_LOGIC- we talked about the need for realistic data types to model busses and drive strength- within VHDL we only have BIT and BIT_VECTOR to model logic gates- these don't work for the real world- we need to use the IEEE.STD_LOGIC_1164.ALL packageSTD_LOGIC - "resolved" data type, scalar (analogous to BIT, but with drive strength)STD_LOGIC_VECTOR - "resolved" data type, vector (analogous to BIT_VECTOR, but with drive strength)- we use this package by entering the following: library IEEE; use IEEE.STD_LOGIC_1164.ALL

  8. STD_LOGIC Data Types • Resolution- These types have the following possible values U = Un-Initialized X = Forcing Unknown 0 = Forcing '0' 1 = Forcing '1' Z = Forcing 'Z' W = Weak Unknown L = Weak '0' H = Weak '1' - = Don't Care- There is a table that VHDL can go to in order to "Resolve" any of the following conditions on a single line ex) 0 and H = 0 0 and 1 = 0 Check for example Wakerly, DDPP, Table 5-24, pp 267.- we will always use these data types (from now on, don't use BIT or BIT_VECTOR)

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