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excuse me, i m a beginner, so the question may be meaningless.
I SIMPLY WROTE MY CODE LIKE:
process(a_in , clk)
begin
if clk'event and clk='1'
then c_out<=a_in;
else c_out<='0';
end if;
end process;
then i met the error like this：＂Can't infer register for 'c_out' at test.vhd(20) because it does not hold its value outside the clock edge".
i think i have wrote "else c_out<=' 0'; " why Quartus II still says it does not hold its value outside the clock edge?
WHEN I CHANGE THE CODE TO:
c_out <= a_in;
if clk'event and clk='1'
then c_out<=a_in;
end if;
IT DOESN'T REPORT ANY ERRORS.
BUT WHEN IT IS
c_out <= '1';
if clk'event and clk='1'
then c_out<=a_in;
end if;
THE SAME ERROR OCCURS.
so, could anyone give some help?
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Hi,
in your code you define a register which is sensitive to the rising clock edge. With the rising edge the register will store the value of the input a_in. The output of a register
could only change at the active edge ( in your case the rising edge). The only possible
else branch is "else c_out <= c_out;" which means store the value until the next rising clock edge.
Kind regards
GPK
Honored Contributor
