ModemSim cannot recognise 'SIGNED' type?

[ZHIQUAN]

I am trying to simulate my program in ModemSim. It gets error
information : Identifier "signed" is not directly visible. What is
the problem?

 

[ZHIQUAN]

Sorry, I forget add some libraries. It works now
ZHIQUAN wrote:

I am trying to simulate my program in ModemSim. It gets error
information : Identifier "signed" is not directly visible. What is
the problem?