GE Hydran 201i Instruction Manual page 254

32-Bit Integer Analog Input Read
Modbus has no support for 32-bit variables. In order to access the Hydran 201Ti's 32-
bit variables, an access must be implemented to 32-bit values.
variables with a value exceeding 16 bits are accessible through the Int32 registers type
in the Modbus Holding Registers map. In this region, all analog values are mapped using
two 16-bit registers.
In the 32-bit mapping, a Hydran 201Ti "Analog Input" object is stored in two
consecutive Modbus 16-bit data objects: the first one is the 16 MSB bits and the second
one is the 16 LSB bits (Big-endian).
In order to ensure data consistency, both parts of a mapped Analog Input object
must be accessed within one Modbus command (function codes 03, 04 or 10). Using
function 06 Preset single holding register with a 32-bit mapping is not possible. If only
part of a 32-bit object mapping is accessed by a Modbus command, the Hydran 201Ti
will respond with an exception code 02 Illegal data address.
32-Bit Floating-Point Analog Input Read
Modbus has no support for 32-bit floating-point variables. In order to access the
Hydran 201Ti's 32-bit floating-point variables, an access must be implemented to 32-bit
values. Floating-point values are mapped using two 16-bit Modbus registers.
In the 32-bit floating-point mapping, a Hydran 201Ti Analog Input object is
represented in binary32 form according to ISO/IEC/IEEE 60559:2011 (IEEE 754)
International Standard. This representation is split in two 16-bit parts which are stored in
two consecutive 16-bit Modbus registers. The first register contains sign, exponent, and 9
most-significant bits of the mantissa. The second register contains 16 least-significant
bits of the mantissa.
In order to ensure data consistency, both parts of a mapped Analog Input object
must be accessed within one Modbus command (function codes 03, 04 or 10). Using
function 06 Preset single holding register with a 32-bit mapping is not possible. If only
part of a 32-bit object mapping is accessed by a Modbus command, the Hydran 201Ti
will respond with an exception code 02 Illegal data address.
J.4.1.2 Strings
Modbus has no native support for Strings; all access string variables must be
wrapped through standard 16-bit registers. The string values are accessible in a specific
region of the Modbus Holding Registers. Each string variable uses 128 X 16-bit registers,
giving a possible string size of 255 bytes. The most-significant byte of the first 16-bit
register specifies the size of the octet string. If the string is shorter than 255 bytes, it is
padded at the end with 00 bytes, which are not counted in the string length.
String Read
To read a specific string object on Modbus, proceed as follows:
Page 254
Hydran* 201i Instruction Manual
All Hydran 201Ti
MA-033 Rev. 14.0, 12-Nov-18