TABLE OF CONTENTS The term register is used for an electronic device in which data can be stored. An internal relay, see Chapter 7, is such a device. The shift register is a number of internal relays grouped together which allow stored bits to be shifted from one relay to another. This chapter is about shift registers and how they can be used where a sequence of operations is required or to keep track of particular items in a production system.
A register is a number of internal relays grouped together, normally 8, 16 or 32. Each internal relay is either effectively open or closed, these states being designated as 0 and 1. The term bit is used for each such binary digit. Therefore, if we have eight internal relays in the register we can store eight 0/1 states. Thus we might have:
and each relay might store an on-off signal such that the state of the register at some instant is:
i.e. relay 1 is on, relay 2 is off, relay 3 is on, relay 4 is on, relay 5 is off, etc. Such an arrangement is termed an 8-bit register. Registers can be used for storing data that originate from input sources other than just simple, single on-off devices such as switches.
With the shift register it is possible to shift stored bits. Shift registers require three inputs, one to load data into the first location of the register, one as the command to...
