procedure TPDO.disconnect;

This method closes a connection. If the connection is already closed, it doesn't do anything. The TPDO will call this method before its destruction, so it's not necessary to explicitly call in that case.

procedure dbtest;
var
    db: TPDO;
begin
    db := TPDO.create;
    if (db.connect('mysql-4.0','10.0.0.152:3306','electronic_catalog','testuser','testpasswd')) then
        writeln ('connection succeeded.')
    else
        writeln ('connection failed.');
    db.disconnect;
    db.free;
end;