# VHDL224: Internal tristates should not be used ## Summary ```{raw} html

Reliability	Security	Maintainability	Code attribute	Effort to fix	Tags

HIGH	-	-	Intentionality \| Logical	1h	synthesis, do254, do254-ss1, vscode, linter, cnes, cnes-std-05400

``` ## Description ```{raw} html

Noncompliant code example

architecture a of e is
begin
  x <= a when (en = '0') else '1';
  y <= b when (en = '0') else 'Z'; -- Noncompliant
  z <= c when (en = '0') else "ZZZZ"; -- Noncompliant
end;

Internal tristates should not be used.

By default, tristate usage is only allowed in top-level entity. Also, a whitelist of allowed usage can be set through the allowedEntities parameter.

``` ## Parameters No parameters. ```{raw} html ```