From the course: PLC Program Flow and Control Instructions

Word shift operations intro - Ladder Logic Tutorial

From the course: PLC Program Flow and Control Instructions

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Word shift operations intro

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- [Tutor] Word shifting operation provides a simpler method of loading and unloading data into a file. Now the word shifting operates this way, rather than shifting bits of information within a word, it shifts the data from a complete word into a file or stack. Two separate shift pulses are required, one to shift data into the file, (load), and one to shift data out of the file, (unload). The movement of data in and out of the file, for word shifting, operates in two ways. The first one is called First In, First Out instruction, (FIFO). The first word enters the file is the first one out. The second instruction, which has the opposite principle is Last In, First Out (LIFO). The last word entered is the first one out. A useful analogy to understand the two types of word shifting instructions is a pile of work on your desk. Let's say a new work arrives, you drop the paper on the top of the stack you already have. If your stack is FIFO, then you pick your work from the bottom of the pile, because you want to use the first one that was placed on your desk. The first one in is the first one out. If the stack is LIFO, then you pick the paper from the top of the pile. The last one came in is the first one to work on. This is another representation to show the differences between FIFO and LIFO. FIFO instruction unloads the words from the file in the same order as the words were entered. The LIFO instruction inverts the order of the data it receives by opening the last data received first. In this section, I'll focus on First In, First Out instruction.

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