Basler DECS-150 - Page 190

25-8 9492600990
Modbus
®
Communication DECS-150
• The next 8 bits are the exponent biased by 127 decimal.
• The 23 LSBs comprise the normalized mantissa. The most-significant bit of the mantissa is always
assumed to be 1 and is not explicitly stored, yielding an effective precision of 24 bits.
The value of the floating-point number is obtained by multiplying the binary mantissa times two raised to
the power of the unbiased exponent. The assumed bit of the binary mantissa has the value of 1.0, with
the remaining 23 bits providing a fractional value. Table 25-3 shows the floating-point format.
Table 25-3. Floating Point Format
Sign Exponent + 127 Mantissa
1 Bit 8 Bits 23 Bits
The floating-point format allows for values ranging from approximately 8.43X10
-37
to 3.38X10
38
. A
floating-point value of all zeroes is the value zero. A floating-point value of all ones (not a number)
signifies a value currently not applicable or disabled.
Example: The value 95,800 represented in floating-point format is hexadecimal 47BB1C00. This number
will read from two consecutive holding registers as follows:
Holding Register Value
K (Hi Byte) hex 1C
K (Lo Byte) hex 00
K+1 (Hi Byte) hex 47
K+1 (Lo Byte) hex BB
The same byte alignments are required to write.
Long Integer Data Format (Uint32)
The Modbus long integer data format uses two consecutive holding registers to represent a 32-bit data
value. The first register contains the low-order 16 bits and the second register contains the high-order 16
bits.
Example: The value 95,800 represented in long integer format is hexadecimal 0x00017638. This number
will read from two consecutive holding registers as follows:
Holding Register Value
K (Hi Byte) hex 76
K (Lo Byte) hex 38
K+1 (Hi Byte) hex 00
K+1 (Lo Byte) hex 01
The same byte alignments are required to write.
Integer Data Format (Uint16) or Bit-Mapped Variables in Uint16 Format
The Modbus integer data format uses a single holding register to represent a 16-bit data value.
Example: The value 4660 represented in integer format is hexadecimal 0x1234. This number will read from
a holding register as follows:
Holding Register Value
K (Hi Byte) hex 12
K (Lo Byte) hex 34
The same byte alignments are required to write.
The Uint16 Data Format is listed in Binary Points (Table 25-6), below.
Example: Register 900 occupies 16 rows in the Register Table where each row gives the name of specific
bit-mapped data such as 900-0 indicates bit 0 of register 900 is mapped to RF-TRIG.