Abstract: Currently used LAdder Diagram（LAD） conversion to Step Ladder Instruction（STL） methods are topological sort，binary tree，generalized form，series and parallel merging and so on.But it is difficult to directly correspond together with the description and the graphics editing in the LAD editing software.The programming for the method is very difficult.To solve the above problems，this paper proposes a merger of equivalent network method.The method uses a matrix and PLC LAD related symbols to describe a LAD，and with a look like the resistor network merging method to implement the merger of LAD.It becomes one of the most simplified merge map，then generates STL from the merge diagram.The method has the advantage in the editing software that is LAD description and conversion to STL operation using the same data structure，and editing software from dynamic rendering trapezoidal integration process.The operation has advantages of intuitive，easy to understand，easy to program and so on.

Key words: embedded PLC, LAdder Diagram（LAD）, Step Ladder Instruction（STL）, equivalent network merging method

摘要： 目前常用梯形图转语句表方法有拓扑排序、二叉树、广义表、串并联归并等，但在梯形图编辑软件中难于直接同图形编辑的描述对应起来，编程难度也较大。为解决这些问题，提出了一种等效网络合并方法，采用一个矩阵和相关的PLC梯形图符号来描述一个梯形图，并用一种类似于电阻网络的合并算法来实现梯形图的合并，变成一个最简化的合并图，然后再从该合并图生成语句表。该方法在编辑软件中梯形图的描述与转语句表运算采用完全相同的数据结构，并可从编辑软件中动态绘制梯形的合并过程，具有直观、易于理解、易于编程等优点。

关键词: 嵌入式PLC, 梯形图, 语句表, 等效网络合并方法