digraph {
  pad=0.5; bgcolor="lightgrey";
  node [shape="box"; style="filled";  fillcolor="cyan"];
  edge [labelfontsize=10; minlen=2; labeldistance=4;  ];
  RTB_IDLE -> RTB_ON [taillabel="EVT_BUTTON"; 
    tailport=sw; headport=nw];
  RTB_ON -> RTB_IDLE [taillabel="EVT_TICK \n&& counter==0\n"; 
    tailport=ne; headport=se];
}