# Shift Registers 370

This class explains the various register shifts than can be used in a PLC.

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## Class Details

Class Name:
Shift Registers 370
Difficulty:
Number of Lessons:
12
Spanish

## Class Outline

• Objectives
• What Is a Shift Register?
• PLC Bits
• Changing Bit Status
• Bit Change Applications
• Shift Register Functions
• Shift Left and Right
• Register Rotate
• Advanced Register Shifts
• Asynchronous Shift Register
• Shift Register Applications
• Summary

## Objectives

• Define shift registers.
• Describe PLC bits.
• Describe bit status change functions.
• Describe bit change applications.
• Describe shift register functions.
• Describe shift left and shift right.
• Describe register rotate.
• Describe advanced register shifts.
• Describe stacking functions.
• Describe shift register applications.

## Glossary

Vocabulary Term Definition
bit clear A PLC function that forces a specified bit to a 0.
bit follow A PLC function that forces a specified bit to a 1 when ON, and a 0 when OFF.
bit set A PLC function that forces a specified bit to a 1.
bit shift left A shift register that shifts each bit one position forward. Shift left is the most common shift register.
bit shift right A shift register that shifts each bit one position backward. Shift right is less commonly used than shift left.
enable bit A status bit that activates PLC functions such as shift registers when the bit is ON.
FIFO The most common stacking function that unloads data in the same order it was received. FIFO stands for first in, first out.
full register rotation Reinserting the shifted out bit back a full 16 bits from where it was last located. Full register rotation is the most common type of register rotation.
LIFO A less common stacking function that unloads data in the opposite order that it was received. LIFO stands for last in, first out.
multiple bit shift An advanced shift register function that shifts bits multiple positions per shift. Sometimes called an N-shift.
multiple shift left An advanced shift register function that shifts bits multiple positions to the left.
multiple shift right An advanced shift register function that shifts bits multiple positions to the right.
N-shift A multiple bit shift register. Called an N-shift because the variable N tells the processor how many positions to shift the bits.
partial register rotation A function that can rotate the bit that was shifted out and insert it back somewhere into the middle of the word instead of at the beginning.
real-time value The exact value of a bit of data. PLC register data is not considered real-time because values can change between PLC scans.
register rotate A PLC function used with shift registers that takes the bit that was shifted out from one end of a word and inserts it at the opposite end of the word. This keeps the bit from being erased and maintains the bit pattern.
rotate left A PLC function that takes the bit that was shifted out from the left end of a word and rotates it back to be inserted into the first bit position on the right.
rotate right A PLC function that takes the bit that was shifted out from the right end of a word and rotates it back to be inserted into the last bit position on the left.
shift register Shifting bits forward or backward within a word to vary how the outputs respond.
stacking function A method of data manipulation that allows you to organize data relative to time and priority.