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Appendix - 71
MELSEC-Q
APPENDICES
BCD (Binary Coded Decimal)
1) This is the abbreviation for "binary coded
decimal", more accurately called a BCD
code. Computers, PLCs, etc., use binary
numbers made up of 1 (ON) and 0 (OFF).
Because this is difficult for humans to
understand, decimal digits are expressed
by a pattern of binary digits. Many of the
digital switches and digital displays used by
humans use a BCD code. The significance
of the bits is shown in the drawing below.
Numbers from 0 to 9,999 can be handled
by 16 bits, and numbers from 0 to
99,999,999 can be handled by 32 bits.
0
B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
4000+1000+800+40+20+10+2 = 5.872
5.872
101100001110010
8000
4
000
2
000
1000
800
400
200
100
80
40
20
10
8
4
2
1
2) BCD commands are commands in which a
binary number (BIN) is converted to a
binary coded decimal (BCD).
They are used to output data from the PLC
and display it on the digital display.
The following drawing shows a 16-bit
example.
0
BIN code
167
000000010100111
0
BCD code
167
000000101100111
Positive/
negative
16384
8192
4096
2048
1024
512
256
128
64
32
16
8
4
2
1
8000
4000
2000
1000
800
400
200
100
80
40
20
10
8
4
2
1
BIAS SPEED AT START
A large amount of torque is required when the
machine starts moving, but the torque may be
unstable at speed 0 with stepping motors.
Therefore, movement can be smoothly carried
out by starting the movement at a given speed
from the beginning. The bias speed at start is
the speed set at that start.
Full speed
Speed 0
Bias speed
BIN (Binary)
1) A binary number, more accurately called a
binary code.
All values are expressed as a binary
number in which 1 turns the PLC, etc.,
electricity ON, and 0 turns it OFF. The
significance of the bits is shown in the
drawing below. In the MELSEC PLC, the
highest order bit (B15) is used to indicate
handling as a positive No. (0), or negative
No. (1), so the 15 bits from B0 to B14 are
valid.
0
B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
128+32+4+2+1=167
167
000000010100111
2
15
2
14
2
13
2
12
2
11
2
10
2
9
2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
Positive/
negative
16384=
8192=
4096=
2048=
1024=
512=
256=
128=
64=
32=
16=
8=
4=
2=
1=
2) BIN commands are commands in which a
binary coded decimal (BCD) is converted to
a binary number (BIN).
They are used to input the data shown on
the digital switch to the PLC.
The following drawing shows a 16-bit
example.
0
BCD code
167
000000101100111
0
BIN code
167
000000010100111
Positive/
negative
8000
4000
2000
1000
800
400
200
100
80
40
20
10
8
4
2
1
16384
8192
4096
2048
1024
512
256
128
64
32
16
8
4
2
1