Programmable Logic Controllers

Chapter 12: Data Handling

Timers, counters and individual internal relays are all concerned with the handling of individual bits, i.e. single on-off signals. Shift registers involve a number of bits with a group of internal relays being linked (see Chapter 11). The block of data in the register is manipulated. This chapter is about PLC operations involving blocks of data representing a value, such blocks being termed words. A block of data is needed if we are to represent numbers rather than just a single on-off input. Data handling consists of operations involving moving or transferring numeric information stored in one memory word location to another word in a different location, comparing data values and carrying out simple arithmetic operations. For example, there might be the need to compare a numeric value with a set value and initiate action if the actual value is less than the set value. This chapter is an introductory discussion of such operations.

12.1 Registers and Bits

A register is where data can be stored (see Section 8.1 for an initial discussion of registers). In a PLC there are a number of such registers. Each data register can store a binary word of usually 8 or 16 bits. The number of bits determines the size of the number that can be stored. The binary system uses only two symbols, 0 and 1 (see Chapter 3). Thus we might have the 4-bit number 1111. This is the denary number, i.e. the familiar number system based on 10...

UNLIMITED FREE ACCESS TO THE WORLD'S BEST IDEAS

close
Already an Engineering360 user? Log in.

This is embarrasing...

An error occurred while processing the form. Please try again in a few minutes.

Customize Your Engineering360 Experience

close
Category: Shift Registers
Privacy Policy

This is embarrasing...

An error occurred while processing the form. Please try again in a few minutes.