255
8-9. Terminology
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 a binary code 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”.
The binary number “0000000000101011” is expressed in decimal as follows:
1
×
2
0
+ 1
×
2
1
+ 0
×
2
2
+ 1
×
2
3
+ 0
×
2
4
+ 1
×
2
5
+ ..... + 0
×
2
15
= 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.
[EXAMPLE]
A number system that uses two symbols, “0” and “1”. Each digit position has
a weighted value of 1, 2, 4, 8, 16, 32, 64, and so on begining with the least
significant (right-most) digit.
The sum of N0 through Nn is the decimal equivalent of the number in base
“2”.
•
Z2
Zn
•
•
•
•
Z3
Z1 Z0
Bit position
Z0
×
2
0
= N0
•
2
n
•
•
•
•
3
1 0
Base = 2
Z1
×
2
1
= N1
Z2
×
2
2
= N2
Z3
×
2
3
= N3
Zn
×
2
n
= Nn
•
•
•
0
0
1
1
Digit position
Decimal
9
3
7
2
0
0
11
1
8
1
0 0
0
3
0
1
15
0
1
12
1 1
0
0
7
4
0 0
Bit position
BCD
•
•
•
•
•
•
•
•
0
0
11
0
8
0
1 1
1
3
0
0
15
0
14 13
0
12
0
10
0
9
0
2 1
0
7
4
0
6
1
5
Bit position
Binary data
Most significant bit
(MSB)
Least significant bit
(LSB)
byte
byte
word
binary:
Binary Coded Decimal (BCD):
binary number system:
Summary of Contents for FP1
Page 1: ...PROGRAMMABLE CONTROLLER FP1 is a global brand name of Matsushita Electric Works Hardware ...
Page 28: ...20 ...
Page 98: ...90 ...
Page 150: ...142 ...
Page 208: ...200 ...
Page 226: ...218 ...
Page 280: ...272 ...
