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Modeling >> Behavioral Models >> problem with detecting falling edge
https://designers-guide.org/forum/YaBB.pl?num=1279807232

Message started by mowiehowie on Jul 22^nd, 2010, 7:00am

Title: problem with detecting falling edge
Post by mowiehowie on Jul 22^nd, 2010, 7:00am

hi all.
i need to detect a falling edge in order to count it and generate a signal. i've made a code like this:
analog begin

@(initial_step) begin

cycle = 0;
carrega = 0;
k = 0;
serial = 0;
vth = 0.9*V(dvdd,dgnd);
end

@(cross(V(clk)-vth, 1)) begin

if (cycle < 71) cycle = cycle + 1; $strobe(cycle);
if (cycle <= 70) serial = $table_model(cycle, "testvector.dat", "D");
if (cycle == 71) cycle = 0;

end

@(cross(V(clk)-vth, -1)) begin

if (k < 71) k = k + 1; $strobe(k);
if (k == 71) carrega = 1; k = 0;

end

V(out_d,dgnd) <+ serial*V(dvdd,dgnd);
V(load,dgnd) <+ carrega*V(dvdd,dgnd);

end

endmodule
in fact, i can see that the rising edge is detected properly but the falling edge is not. k only reaches '1'. it doesnt increase anymore.

what might be going on?

Title: Re: problem with detecting falling edge
Post by Geoffrey_Coram on Jul 22^nd, 2010, 12:12pm

A stupid trick for checking this might be to change
@(cross(V(clk)-vth, -1)) begin
to this:
@(cross(vth-V(clk), 1)) begin