Programming instructions

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LESSON 4 – Numbering Systems
The PLC uses several numbering systems besides the Base 10 decimal system. An
understanding of these other systems is crucial to successful programming.
Lesson Objectives: At the conclusion of this lesson, you will be able to…
9 Name the different numbering systems.
9 Describe how the different systems represent numbers.
9 Convert between number systems.
Materials: FX-Series PLC Training Manual
4.1 Binary Numbers
In the binary number system, each digit is called a binary unit, or bit for short.
Binary is a Base 2 numbering system, meaning there are only 2 possible values
for each digit. Each bit can have a value of only ‘0’ or ‘1’.
A group of 4 bits is called a NIBBLE
A group of 8 bits is called a BYTE
A group of 16 bits is called a WORD
The position of a bit, in a byte or word, determines its value. Starting from the
right side, bit number 0 has a value of ‘1’. As you move left, the bit value doubles
with each position. Bit 1 has a value of 2, bit 2 has a value of 4, bit 3 has a value
of 8, etc.
The following example shows a BYTE:
Bit Value
128 64 32 16 8 4 2 1
0 0 0 0 0 0 0 0
7 6 5 4 3 2 1 0
Bit Number