请教大家如何用S7最简单的梯形图实现以上功能.

  ITEM#1  ITEM#2  ITEM#3  ITEM#4
device#1     on    on
device#2    on   on
device#3    on   on
device#4     on    on   on
device#5     on    on    on
  0s     20s   40s    60s   80s

device#1--device#5按上表顺序起停,按下启动按扭20后#1,4#,#5启动,
再过20S后#2,#3,#5启动,依次类推,最后过20S后从ITEM#4返回ITEM#1,
如此往复循环,直至按下停止按扭.
启动:I0.0 停止:I0.1
device#1--device#5:Q0.0;Q0.1;Q0.2;Q0.3;Q0.4;