ladder with verilogams

[scoobydoo]

adder with verilogams

hey all

i have programmed a fulladder with verilogams by implementing its truth table
and using the transition. The truth table assigns the values to "sum" and "carry" and finally the transistion function is used as follows
V(sumout) <+ transition (sum, td, td)
V(carryout) <+ transition (carry, td, td).

this full adder was wired to a 4bit carry ripple adder.
for constant input voltages summing is working fine but as far as i´m using pulses at the input i´m receiving spikes?
what could that be and what could i do to prevent that?

regards scoobydoo

 

[skal81]

You're problem is probably not coming from the "transition" function, but from the calculation of "sum" and "carry".
You should try to check the detection command (always @.....) used.
There are few information in your post, but I think that
- you have a detection on the edge of each of the input
- due to this when using pulses the numeric value of "sum" and "carry" take intermediate values
- those values are presented on the output through the transition
If so, try to check the condition of calculation of the signals.
An other solution, is to increase the transition time (second td parameter of the function) so that the spikes do not appear anymore.