a digital circuit toolbox. verilog hierarchy each design identifier creates a new branch of the...
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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
Bidirectional Busses
• The signals is divided into two parts:
the driver part
input part• The two parts are then
wired together
If/else Priority Encoder
• Implied priority with precedence assigned to the first instruction encountered in a begin/end block
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 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
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