Define Bit, Byte, Word, Double Word

In connection with programmable controllers, terms such as BIT, BYTE and WORD are frequently used in the explanation of data and/or data processing.

BIT

Bit is the abbreviation for binary digit. The BIT is the smallest binary (bivalent) information unit, which can accept a signal status of “1“ or “0“.

 BYTE

For a unit of 8 binary characters, the term BYTE is used. A byte has the size of 8 bits.

 WORD

A word is a sequence of binary characters, which is regarded as a unit in a specific connection. The word length corresponds to the number from 16 binary characters. With words, the following can be represented:

A word also has the size of 2 bytes or 16 bits.

DOUBLE-WORD

A double-word corresponds to the word length of 32 binary characters.

A double-word also has the size of 2 words, 4 bytes, or 32 bits.

Further units are kilo-bit or kilo-byte, which stand for 210, or 1024 bits, and the mega-bit or mega-byte which stands for 1024 kilo-bits.

BIT ADDRESS

So that individual bits can be addressed within a byte, each individual bit is assigned a bit location. In each byte the bit gets the bit location 7 on the leftmost side and the bit location 0 on the rightmost side.

BYTE ADDRESS

The individual bytes also receive numbers called byte displacements. Additionally, the operand is still marked, so that e.g. IB 2 stands for input byte 2 and QB4 stands for output byte 4. Individual bits are clearly addressed by the combination of bit and byte displacement. The bit location is separated from the byte displacement by one point. The bit location stands to the right of the point, and the byte displacement to the left.

WORD ADDRESS

The numbering of words results in a word address.

Note: The word address is always the smallest address of the two pertinent bytes when using words, e.g. input word(IW),output word(QW), bit memory word(MW), etc. (e.g. With a

word that comes from IB2 and IB3, the address is IW2).

Note: During word processing it is to be noted that e.g. the input word 0 and the input word 1 are in a byte overlap. In addition, when counting bits, one begins at the rightmost bit.

For example the bit0 from IW1 is the bit of I2.0, bit1 is I2.1…. bit7 is I 2.7, bit8 is

I1.0…. bit15 ois I1.7. A jump exists between the bits 7 and 8.

DOUBLE-WORD ADDRESS

The numbering of double-words results in a double-word address.

Note: When using double-words e.g. ID,QD,MD etc. the double-word address is the smaller

word address of the two pertinent word.