10327: can't determine definition of operator ""=""

[artvandelay]

Hello!

As the titles describes I get this error when trying to compile:
Error (10327): VHDL error at ps2lab1.vhd(126): can't determine definition of operator ""="" -- found 0 possible definitions

I have defined at the top of my code:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

this is the part with the error:

PROCESS (scan_ready)
BEGIN
IF (scan_ready'EVENT AND scan_ready = '1') THEN
history(4) <= history(3);
history(3) <= history(2);
history(2) <= history(1);
history(1) <= scan_code;
END IF;
END PROCESS;

I don't understand why this won't work. Any idea?

 

[jeppe]

Which type used for the signal "scan_ready" ?

 

[artvandelay]

boolean signal for scan_ready

 

[joris]

If it is a boolean, you should not compare to '1'; you can use it without an explicit comparison:

PROCESS (scan_ready)
BEGIN
IF (scan_ready'EVENT AND scan_ready) THEN
--code
END IF;
END PROCESS;

Or, if you prefer, you can explicitly compare to true:

PROCESS (scan_ready)
BEGIN
IF (scan_ready'EVENT AND scan_ready = true) THEN
--code
END IF;
END PROCESS;