Endress+Hauser EngyVolt RV15, Руководство по эксплуатации

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EngyVolt RV15 Appendix
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LSB = ErrorWord AND Hex (0001)
IF LSB = 1 THEN ErrorWord = ErrorWord – 1
ErrorWord = ErrorWord / 2
IF LSB = 1 THEN ErrorWord = ErrorWord XOR Hex (A001)
NEXT bit in byte
NEXT Byte in message
END
11.4.6 Function codes
The function code part of a Modbus Protocol message defines the action to be taken by the slave.
EngyVolt devices support the following function codes:
Code Modbus protocol name Description
03 Read Holding Registers Read the contents of read/write location (4X references).
04 Read Input Registers Read the contents of read only location (3X references).
08 Diagnostics Only sub-function zero is supported. This returns the data
element of the query unchanged.
16 Pre-set Multiple Registers Set the contents of read/write location (4X references).
11.4.7 IEEE floating point format
The Modbus Protocol defines 16 bit “Registers” for the data variables. A 16-bit number would prove
too restrictive, for energy parameters for example, as the maximum range of a 16-bit number is
65535. However, there are a number of approaches that have been adopted to overcome this
restriction. Integra Digital meters use two consecutive registers to represent a floating-point number,
effectively expanding the range to ±1 x 10
37 .
The values produced by EngyVolt devices can be used directly without any requirement to “scale”
the values, for example, the units for the voltage parameters are volts, the units for the power
parameters are watts etc.
What is a floating point number?
A floating-point number is a number with two parts, a mantissa and an exponent and is written in
the form 1.234 x 10
5 . The mantissa (1.234 in this example) must have the decimal point moved to
the right with the number of places determined by the exponent (5 places in this example) i.e.
1.234 x 10
5 = 123 400.
If the exponent is negative the decimal point is moved to the left.
What is an IEEE 754 format floating-point number?
An IEEE 754 floating point number is the binary equivalent of the decimal floating-point number
shown above. The major difference being that the most significant bit of the mantissa is always
arranged to be 1 and is thus not needed in the representation of the number. The process by which
the most significant bit is arranged to be 1 is called normalisation, the mantissa is thus referred to
as a “normal mantissa”. During normalisation the bits in the mantissa are shifted to the left whilst
the exponent is decremented until the most significant bit of the mantissa is one. In the special case
where the number is zero both mantissa and exponent are zero. The bits in an IEEE 754 format
have the following significance:
Data Hi Reg, Hi Byte. Data Hi Reg, Lo Byte. Data Lo Reg, Hi Byte. Data Lo Reg, Lo Byte.
SEEE
EEEE EMMM
MMMM MMMM
MMMM MMMM
MMMM
Where: