In the following tables:
S0 – S23 are the significand bits from least to most significant.
E0 – E7 are the exponent bits from least to most significant.
Sign is 1 if the number is negative, and 0 if the number if positive.
Lower numbered register
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
S15 S14 S13 S12 S11 S10 S9
S8
S7
S6
S5
S4
S3
S2
S1
S0
Higher numbered register
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Sign E7
E6
E5
E4
E3
E2
E1
E0
S22 S21 S20 S19 S18 S17 S16
Since the Modbus register data is sent most significant byte first and the registers are sent
lowest numbered first, a floating point value will look like this in the data stream:
First byte (MSB of lower register)
Data bit 7
6
5
4
3
2
1
0
Value bit S15
S14
S13
S12
S11
S10
S9
S8
Second byte (LSB of lower register)
Data bit 7
6
5
4
3
2
1
0
Value bit S7
S6
S5
S4
S3
S2
S1
S0
Third byte (MSB of higher register)
Data bit 7
6
5
4
3
2
1
0
Value bit Sign
E7
E6
E5
E4
E3
E2
E1
Fourth byte (LSB of higher register)
Data bit 7
6
5
4
3
2
1
0
Value bit E0
S22
S21
S20
S19
S18
S17
S16
Example: Set the gas mix as 60% methane and 40% nonane.
This requires setting the thirty-four registers 40058 through 40091. Register pair 40058-40059
will be set to 60.0, register pair 40090-40091 will be set to 40.0, and the rest of the register
pairs between them will be set to 0.0.
85
Model FT4X
COMMUNICA
TIONS
Communications: Modbus