Verilog – Combinational Logic - Worcester Polytechnic Institute
[Pages:33]Verilog ? Combinational Logic
Verilog for Synthesis
Jim Duckworth, WPI
1
Verilog Module Rev A
Verilog ? logic and numbers
? Four-value logic system
? 0 ? logic zero, or false condition ? 1 ? logic 1, or true condition ? x, X ? unknown logic value ? z, Z - high-impedance state
? Number formats
? b, B binary ? d, D decimal (default) ? h, H hexadecimal ? o, O octal
? 16'H789A ? 16-bit number in hex format ? 1'b0 ? 1-bit
Jim Duckworth, WPI
2
Verilog Module Rev A
Verilog types
? Constants
? parameter ? parameter ? parameter
DIME = 10; width = 32, nickel = 5; quarter = 8'b0010_0101;
? Nets
? wire ? wire[7:0]
clock, reset_n; a_bus;
? Registers
? reg ? reg[7:0]
clock, reset_n; a_bus;
? Integer
? only for use as general purpose variables in loops
? integer
n;
Jim Duckworth, WPI
3
Verilog Module Rev A
Operators
? Bitwise
? ~ negation ? & and ? | inclusive or ? ^ exclusive or ? ?
Verilog y = a & b; y = a | b; y = a ^ b; y = ~(a & b); y = ~ a;
VHDL y = a AND b; y = A OR b; y = a XOR b; y = A NAND b; y = NOT a;
? Reduction (no direct equivalent in VHDL)
? Accept single bus and return single bit result
? & and
y = & a_bus;
? ~& nand
? | or
y = | a_bus;
? ^ exclusive or
Jim Duckworth, WPI
4
Verilog Module Rev A
Operators (cont'd)
? Relational (return 1 for true, 0 for false)
? < less than,
greater than >=
? Equality
? == logical equality ? != logical inequality
? Logical Comparison Operators
?! ? && ? ||
logical negation logical and logical or
? Arithmetic Operators
?+ ??*
Jim Duckworth, WPI
5
Verilog Module Rev A
Operators (cont'd)
? Shift
? >
logical shift left, (> arithmetic)
? Conditional
? Only in Verilog - selects one of pair expressions
? ?: ? Logical expression before ? is evaluated ? If true, the expression before : is assigned to output ? If false, expression after : is assigned to output
? Y = (A > B) ? 1 : 0 ? Y = (A == B) ? A + B : A ? B
Jim Duckworth, WPI
6
Verilog Module Rev A
Simple Combinational Example
Jim Duckworth, WPI
7
Verilog Module Rev A
View Technology Schematic
Jim Duckworth, WPI
8
Verilog Module Rev A
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