Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 199)

11–3 Data Encoding
Publication 1770Ć6.5.16 - October 1996
Binary
The binary numbering system is a simple method for computer and
PLC applications because it is the most natural way to represent data
bits. However, since the binary system uses the digits 0 and 1, it is
cumbersome to show values in binary format.
Each digit in a binary number has a place value expressed as a power
of 2. You calculate the decimal equivalent of a binary number by
multiplying each binary digit by its corresponding place value and
then adding the results of the multiplications.
Binary Representation, Number 239
Bit:
1
2
1 1 0 1 1 1 1
7 6 5 4 3 1 0
1 x 2 7 = 128
1 x 2 6 = 64
1 x 2 5 = 32
1 x 2 4 = 0
1 x 2 3 = 8
1 x 2 2 = 4
1 x 2 1 2
1 x 2 0 1
239
10
Binary Coded Decimal
PLC data is often represented in binary coded decimal (BCD) form.
In this system, each group of four bits in a PLC word represents one
decimal number between 0 and 9. In this way, each 16-bit word can
represent a BCD value between 0 and 9,999. Many PLCs use only a
three-digit BCD (12 bits). The upper digit (3 bits) is used for
information such as timer or counter status.
BCD Representation of Decimal 239
0 0 1 1
third digit
0 1 1 0
second digit
0 1 0 0
first digit
0 x 2 3 = 0
0 x 2 2 = 0
1 x 2 1 = 2
0 x 2 0 = 0
0 x 2 3 = 0
0 x 2 2 = 0
1 x 2 1 = 2
1 x 2 0 = 1
1 x 2 3 = 8
0 x 2 2 = 0
0 x 2 1 = 0
1 x 2 0 = 1
= 2
10
= 3
10
= 9
10
= 239
10