Panasonic FP3 Technical Manual page 139

binary:
Binary Coded Decimal (BCD):
In general, programmable controllers work with binary numbers in one form or
another to represent various codes or quantities. The binary number system uses the
number 2 as the base and the only allowable symbols are "0" and "1". There are no
2s, 3s, etc. Each digit of binary is called as "bit". "Bit" means "binary digit". A group
of 8 bits is called a "byte" and a group of 16 bits (two bytes) is called a "word".
Most significant bit
(MSB)
Bit position 15 14 13 12 11 10 9
Binary data 0 0 0
The binary number "0000000000101011" is expressed in decimal as follows:
0 1 2
1×2 + 1×2 + 0×2 + 1×2
= 1 + 2 + 0 + 8 + 0 + 32 + ..... + 0
= 43
One of the codes expressed in binary. BCD is a binary code in which each decimal
digit from 0 to 9 is represented by four binary digits (bits). The four positions have
a weighted value of 1, 2, 4, and 8, respectively, starting with the least significant bit.
A thumbwheel switch is specified as a BCD device, and when connected to a
programmable controller, each decimal digit requires four inputs.
BCD is usually expressed grouping four bits as one digit in the same way as the
hexadecimal constant H. When BCD is grouped in four bit units, the BCD is
expressed by adding the prefix H to the data. Since the weight of each BCD H
code is same as that of decimals, be sure to pay attention not to be confused with
hexadecimal numbers when BCD H code is handled.
Example: When K1993 (decimal) is expressed in BCD.
K1
Decimal
BCD code
0 0 0 1
H1
BCD H code
8 7
0 0 0 0 0 0
byte
word
3 4 5
+ 0×2 + 1×2 + ..... + 0×2
9 9 3
1 0 0 1 1 0 0 1 0 0 1 1
9 9 3
1
× 9 = 90
10
2
× 9 = 900
10
3 × 1 = 1000
10
8-6. Terminology
Least significant bit
(LSB)
6 5 4 3 2 1 0
0 1 0 1 0 1 1
byte
15
0 × 3 = 3
10
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