Appendix
PROFIBUS manual
Version FELD-V2002.02
Page 37
x = -0,25
is represented as -1.0 * 2
-2
, i.e.
sign bit (
sign
):
1 (negative)
exponent (
ex
):
125
Æ
125 –
127
= -2
mantissa (
mant
):
0.0
Æ
0.0 +
1.0
= 1.0
giving:
25
.
0
4
1
*
0
.
1
2
1
*
0
.
1
0
.
1
*
2
*
)
1
(
)
0
.
0
0
.
1
(
*
2
*
)
1
(
2
2
)
127
125
(
1
−
=
−
=
−
=
−
=
+
−
=
−
−
x
Encoding of the three formula components in the four bytes
1st byte (first byte)
Bit 7
MSB
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
LSB
S E
7
E
6
E
5
E
4
E
3
E
2
E
1
2nd byte (second byte)
Bit 7 Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
E
0
M
22
M
21
M
20
M
19
M
18
M
17
M
16
3rd byte (third byte)
Bit 7 Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
M
15
M
14
M
13
M
12
M
11
M
10
M
9
M
8
4th byte (fourth byte)
Bit 7 Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
M
7
M
6
M
5
M
4
M
3
M
2
M
1
M
0
•
The bit S in the first byte contains the sign bit
•
The bits E
7
– E0 in bytes 1 and 2 form the exponent
•
The bits M22 – M0 in bytes 2 - 4 form the mantissa