In-Situ Aqua TROLL 400 Modbus and SDI-12 Reference Guide - Manual (Page 64)

8.11.4 Unsigned Long
A 4-byte unsigned integer contained in two register data address’s. IEEE standard.
8.11.5 Float
IEEE 4-byte numeric standard – 1 sign bit, 8-bit exponent, 23-bit mantissa.
Where S = sign bit, X = exponent bits and M = mantissa bits.
8.11.6 Double
IEEE 8-byte numeric standard – 1 sign bit, 11-bit exponent, 64-bit mantissa.
Where S = sign bit, X = exponent bits and M = mantissa bits.
8.11.7 Character
A 2 byte Unicode character contained with a single register data address.
8.11.8 String
The number of consecutive registers in the register map will represent the maximum string
length in Unicode characters excluding any termination characters. For example, a 6-register
string can have 6 Unicode characters. When reading/writing a string, all register values must be
transmitted. If the string to be written does not require the full defined field length, the extra
bytes must be padded with the value 0x0000 to reach full length. A string termination character
is not required. All registers may contain a character. Failure of the Master device to transmit or
request all registers of a string field will be rejected by the Slave device with the Modbus
exception error code 0x80.
Byte 7 Byte 2 Byte 1 Byte 0
SXXX XXXX XXXX MMMM MMMM MMMM MMMM MMMM … MSB LSB
Byte 3 Byte 2 Byte 1 Byte 0
SXXX XXXX XMMM MMMM MMMM MMMM MMMM MMMM MSB LSB
Byte 2 Byte 3 Byte 1 Byte 0
XXXX XXXX XXXX XXXX MSB LSB XXXX XXXX XXXX XXXX
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