ABB DAI04 模块 (ABB S800 通讯卡)

ABB DAI04 模块 (ABB S800 通讯卡)

ABB DAI04 模块 (ABB S800 通讯卡)

ABBDAI04当PLC控制器投入运行后，其工作过程一般分为三个阶段，即输入采样、用户程序执行和输出刷新三个阶段。完成上述三个阶段称作一个扫描周期。在整个运行期间，PLC控制器的CPU以一定的扫描速度重复执行上述三个阶段。

在输入采样阶段，PLC控制器以扫描方式依次地读入所有输入状态和数据，并将它们存入I/O映象区中的相应得单元内。输入采样结束后，转入用户程序执行和输出刷新阶段。在这两个阶段中，即使输入状态和数据发生变化，I/O映象区中的相应单元的状态和数据也不会改变。因此，如果输入是脉冲信号，则该脉冲信号的宽度必须大于一个扫描周期，才能保证在任何情况下，该输入均能被读入

在用户程序执行阶段，PLC控制器总是按由上而下的顺序依次地扫描用户程序(梯形图)。在扫描每一条梯形图时，又总是先扫描梯形图左边的由各触点构成的控制线路，并按先左后右、先上后下的顺序对由触点构成的控制线路进行逻辑运算，然后根据逻辑运算的结果，刷新该逻辑线圈在系统RAM存储区中对应位的状态;或者刷新该输出线圈在I/O映象区中对应位的状态;或者确定是否要执行该梯形图所规定的特殊功能指令。

ABB DAI04 模块 (ABB S800 通讯卡)

When the PLC controller is put into operation, its working process is generally divided into three stages, namely input sampling, user program execution and output refresh three stages. Completing these three stages is called a scan cycle. During the entire operation period, the CPU of the PLC controller repeats the above three stages at a certain scanning speed.

In the input sampling phase, the PLC controller reads all the input status and data successively by scanning and stores them in the corresponding unit in the I/O image area. After the end of the input sampling, the user program execution and output refresh phase. In both phases, even if the input state and data change, the state and data of the corresponding unit in the I/O map area will not change. Therefore, if the input is a pulse signal, the width of the pulse signal must be greater than one scan cycle to ensure that the input can be read in any case

In the execution phase of the user program, the PLC controller always scans the user program in sequence from top to bottom (ladder diagram). When scanning each ladder diagram, it always scans the control line composed of each contact on the left side of the ladder diagram first, and carries out logical operations on the control line composed of contacts in the order of first left and then right, first up and then down, and then refreshes the status of the corresponding bit of the logic coil in the system RAM storage area according to the results of logical operations; Or refresh the state of the corresponding bit of the output coil in the I/O map area; Or determine whether to execute the special function instructions specified in the ladder diagram.