S7-1200编程中的EN/ENO机制

作为一个菜鸟，又要麻烦大家，请教大家问题：

按照手册中说明，激活EN/ENO机制方法：

1. 在程序中，右键单击待激活 EN/ENO 机制的指令。

2. 在快捷菜单中，选择“生成 ENO”(Generate ENO) 命令。将再次生成指令的 ENO 值。如果激活使能输出，则随后将插入其它指令。

可我右键单击指令后，“生成ENO”、“不生成ENO”是灰色的，不能选，麻烦大家帮我看下啥原因。

Basics of the EN/ENO mechanism   

Glossary 

Enabling and disabling the EN/ENO mechanism 

Introduction

Runtime errors that require a program abort can occur during the processing of instructions. You can use the EN/ENO mechanism to avoid such program aborts. This mechanism can be used at two levels:

EN/ENO mechanism for individual instructions

EN/ENO mechanism for block calls

EN/ENO mechanism for instructions in LAD/FBD

In LAD and FBD, certain instructions have an enable input EN and an enable output ENO. 

You can use the enable input EN to make the execution of the instruction dependent on conditions. The instructions are only executed if the signal state is "1" at the enable input EN. 

You can use the enable output ENO to query runtime errors in instructions and react to these.

The enable output ENO returns the signal state "1" if one of the following conditions applies:

No error occurred during processing.

The enable output ENO returns signal state "0" if one of the following conditions applies:

The EN input has signal state "0".

An error occurred during processing.

The EN/ENO mechanism is used for the following basic instructions:

Mathematical functions

Move operations

Conversion operations

Word logic operations

Shift + rotate

上面是EN/ENO机制的在线help摘录。你操作截图说明，你编程没有在需要或可以激活EN/ENO的状态环境，所以菜单显示的虚的。

谢谢！我还是要继续琢磨琢磨，然后再请教！