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VHDL signals vs variables in sims and synthesis

Signals have associated time parameter and retains it value in time till a new assignment is established at discrete time. These sequence of assignments when plotted with incremental time results is a nice display. This display is a digital waveform.
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Shim Events, Trans Logic Values Signals
variable
A
1
variable
B
3
variable
C
5
result
Y
0
Wait on Event
trigger
0
1
B
A
1
C
B
1
A
C
1
Result
A+B+C
3
signal
A
1
signal
B
3
signal
C
5
result
Y
0
Wait on Event
trigger
0
1
B
A
1
C
B
3
A
C
5
Result
A+B+C
9

In comparison variables only associate with a current value.

 

So a note from above description: In case of a new assignment:-

Variables will get updated instantaneously.  

Whereas, signals will get the new value only at next discrete time interval. So there is a possibility of a delta delay before the signals get updated.

 

This delta delay is a duration for a Process to finish all its computational tasks.

 

 

VHDL signals and variables in synthesis -

Signals are most important components for digital design and these are used all over the architecture of design.   

Variables are also allowed to be synthesized for hardware.

 

Examples for variables and signals discussed next.

Interview Questions. Main, FPGA, Digital Fundamentals

The result will get updated when event trigger goes from 0 to 1

Interview Questions. Main, FPGA, Digital Fundamentals
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