a digital circuit toolbox
DESCRIPTION
A Digital Circuit Toolbox. Verilog Hierarchy. Each design identifier creates a new branch of the hierarchy tree. Tristate Signals and Busses. Tristate busses are allowed by most FPGA architectures on devices output pins - PowerPoint PPT PresentationTRANSCRIPT
A Digital Circuit Toolbox
Verilog Hierarchy
• Each design identifier creates a new branch of the hierarchy tree
Tristate Signals and Busses
• Tristate busses are allowed by most FPGA architectures on devices output pins
• If tristate are not allowed,the synthesis may have
control to automatically substitutes with MUXes
Schematics for Internal Tristate Buffer Design
MUX version of Tristate Buffer Design
Bidirectional Busses
• The signals is divided into two parts:
the driver partinput part
• The two parts are then wired together
Bidirectional Busses
If/else Priority Encoder
• Implied priority with precedence assigned to the first instruction encountered in a begin/end block
If/else Priority Encoder
Case Priority Encoder
• The cases aremutually exclusive and do not overlap
State Machines• Use a set of registers, to determine current
machine state• Moore style :
the output depends only on the state
• Mealy style: the output depends on the state and some input signals
State Machines
State Machines
Converting Binary to Gray Code
Converting Gray Code to Binary
State Assignment
• Make a big difference in how efficiently your logic will be synthesize
• use parameters, ‘define and ‘ifdef
to select between encoding assignments
State Assignment
• One-hot state assignment means that each state is assigned a single state flip-flop which is active only in the assigned state
• One-could state assignment means that a flip-flop is inactive only in the assigned state
AddersHalf-Adder
• The synthesis tool will examine each instance of the + operator and will try to implement the logic with a preoptimized module
Half-Adder
Full Adder
• To turn the half adder into a full adder, we take the output of a half adder and connect it into another half adder
Full Adder
Full Adder
Full Adder
Subtractor
• Similar to the adder
Full-Subtractor
Hard-Wired Multipliers
• Multiply value by a constant
• The multiplication process shifts and adds
Generic Multipliers
• We must create logic which allows all the shift and adds to be used