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FX Series Programmable Controllers Devices in Detail 4
4-37
4.14 Bits, Words, BCD and Hexadecimal
The following section details general topics relating to good device understanding. The section
is split into several smaller parts with each covering one topic or small group of topics. Some of
the covered topics are;
Bit devices, individual and grouped - see page 4-40
Word devices - see page 4-42
Interpreting word data - see page 4-42
Two’s compliment - see page 4-45
Available devices:
• For PLC specific available devices please see chapter 8.
4.14.1 Bit Devices, Individual and Grouped
Devices such as X, Y, M and S are bit devices. Bit devices are bi-stable, this means there are
only two states, ON and OFF or 1 and 0. Bit devices can be grouped together to form bigger
representations of data, for example 8 consecutive bit devices are some-times referred to as a
byte. Further more, 16 consecutive bit devices are referred to as a word and 32 consecutive bit
devices are a double word.
The PLC identifies groups of bit devices which should be regarded as a single entity by looking
for a range marker followed by a head address. This is of the form KnP where P represents the
head address of the bit devices to be used. The Kn portion of the statement identifies the
range of devices enclosed. “n” can be a number from the range 0 to 8. Each “n” digit actual
represents 4 bit devices, i.e K1 = 4 bit devices and K8 = 32 bit devices. Hence all groups of bit
devices are divisible by 4.
The diagram and example on the following page explain this idea further........