前几天，我在西门子A&D服务与支持的英文论坛上同样问了这个问题，得到的答复是：
Siemens has a Special family of equipments to do these tasks (SICAM) with 1ms resolution.

You can use IM153 and DI modules with diagnostic / process interrupt, but I can’t estimate a resolution. Other alternative would be a Profinet IO (Isochronous real-time - IRT mode) with takt of 1ms and jitter of 1 micro second but I’m not sure about the details.

从他的回答中看出，能够实现硬件SOE的只有SICAM和实时以太网两种方案，否则只能软件编程。我使用软件编程的方式作了软SOE，优点是数据量大(超过一千点，每点能监视0->1和1->0变位，除实点外还能监视虚点，也就是程序中的逻辑标志)，缺点是分辨率为一个程序扫描周期(目前为40-70 ms)。