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FX Series Programmable Controllers Devices in Detail 4
4-40
4.14 Bits, Words, BCD and Hexadecimal
The followin
g
section details
g
eneral topics relatin
g
to
g
ood device understandin
g
. The section
is split into several smaller parts with each coverin
g
one topic or small
g
roup of topics. Some of
the covered topics are;
Bit devices, individual and
g
rouped - see pa
g
e 4-40
Word devices - see pa
g
e 4-42
Interpretin
g
word data - see pa
g
e 4-42
Two’s compliment - see pa
g
e 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
onl
y
two states, ON and OFF or 1 and 0. Bit devices can be
g
rouped to
g
ether to form bi
gg
er
representations of data, for example 8 consecutive bit devices are some-times referred to as a
b
y
te. Further more, 16 consecutive bit devices are referred to as a word and 32 consecutive bit
devices are a double word.
The PLC identifies
g
roups of bit devices which should be re
g
arded as a sin
g
le entit
y
b
y
lookin
g
for a ran
g
e marker followed b
y
a head address. This is of the form Kn
P
where
P
represents the
head address of the bit devices to be used. The Kn portion of the statement identifies the
ran
g
e of devices enclosed. “n” can be a number from the ran
g
e 0 to 8. Each “n” di
g
it actual
represents 4 bit devices, i.e K1 = 4 bit devices and K8 = 32 bit devices. Hence all
g
roups of bit
devices are divisible b
y
4.
The dia
g
ram and example on the followin
g
pa
g
e explain this idea further........