From this you can determine the following information.
·
The sign bit is 0, indicating a positive number.
·
The exponent value is 10000110 binary or 134 decimal. Subtracting 127 from 134 leaves 7,
which is the actual exponent.
·
The mantissa appears as the binary number 11100001000000000000000
There is an implied binary point at the left of the mantissa that is always preceded by a 1. This
bit is not stored in the hexadecimal representation of the floating-point number. Adding 1 and
the binary point to the beginning of the mantissa gives the following:
1.11100001000000000000000
Now, we adjust the mantissa for the exponent. A negative exponent moves the binary point to
the left. A positive exponent moves the binary point to the right. Because the exponent is 7, the
mantissa is adjusted as follows:
11110000.1000000000000000
Finally, we have a binary floating-point number. Binary bits that are to the left of the binary
point represent
the power of two corresponding to their position. For example, 11110000 represents (1 x 2
7
) +
(1 x 2
6
) + (1x 2
5
) + (1 x 2
4
) + (0 x 2
3
)+ (0 x 2
2
) + (0 x 2
1
)+ (0 x 2
0
) = 240.
Binary bits that are to the right of the binary point also represent a power of 2 corresponding to
their position. As the digits are to the right of the binary point the powers are negative. For
example: .100 represents (1 x 2
-1
) + (0 x 2
-2
)+ (0 x 2
-3
) + … which equals 0.5.
Adding these two numbers together and making reference to the sign bit produces the number
+240.5.
For each floating point value requested two MODBUS Protocol registers (four bytes) must be
requested. The received order and significance of these four bytes for Eastron Digital meters is
shown below:
Data Hi Reg,
Hi Byte
Data Hi Reg,
Lo Byte
Data Lo Reg,
Hi Byte
Data Lo Reg,
Lo Byte
3.8 MODBUS Protocol Commands supported
All Eastron
Digital meters support the “Read Input Register” (3X registers), the “Read Holding
Register” (4X registers) and the “Pre-set Multiple Registers” (write 4X registers) commands of
the MODBUS Protocol RTU protocol. All values stored and returned are in floating point format
to IEEE 754 with the most significant register first.
3.8.1 Read Input Registers
MODBUS Protocol code 04 reads the contents of the 3X registers.
Example
The following query will request ‘Volts 1’ from an instrument with node address 1:
Field Name
Example(Hex)
Slave Address
01
Function
04
Starting Address High
00
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