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. ...
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