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9. Modbus register map
POWER XPERT® RELEASE TRIP UNIT FOR MAGNUM PXR CIRCUIT BREAKERS MN013015EN January 2022 www.eaton.com
9.3.2 Two and four register data formats
Format of two register (4 bytes) or four registers (8 bytes)
data.
Table 22. Modbus multiple register data format.
2 register format Integer 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Register number Low 16 bits
Register number + 1 High 16 bits
2 register format IEEE float 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Register number Fraction
Register number + 1 Sign Exponent Fraction
4 register format Integer 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Register number Byte 1 of mantissa Byte 0 of mantissa
Register number + 1 Byte 3 of mantissa Byte 2 of mantissa
Register number + 2 Byte 5 of mantissa Byte 3 of mantissa
Register number + 3 Engineering units Mantissa multiplier
Calculation: Energy = 2
mantissa multiplier
* 48-bit mantissa * 10
engineering units
9.3.3 Mapped register configuration
A block of registers can be established in trip unit to remap
up to 100 data objects.
The remapping assignments are stored beginning at 1001;
only the first data object address is used. For example,
although data object IA occupies 0x1202 and 0x1203, only
0x1202 is loaded into the assignment register. Data object
length is important to account function code 16 is used to
load the object assignments in a single write and all object
assignments must be valid.
Data from to the assigned objects is read from registers
starting at 1201 and continuing for each object assigned. It
is important to account for data object length. The number
of objects and their placement order is dependent on the
configuration of the assignment registers. The starting
address must be aligned with the start of an object and the
number of registers to obtain must align with the end of an
object.
Table 23. Modbus mapped registers.
Func.
code
Register
number
Address
(hex)
Length R/W Definition
3,4,16 1001 0x03E8 100 R/W Block of 100 registers for
the mapping assignments.
3,4 1201 0x04B0 200 R Data that has been
remapped (200 registers
maximum).
9.4 Setpoint registers
The trip unit’s setpoints are organized into groups. Group 0
is the system group which provides information about the
circuit breaker and trip unit. Group 1 is the protection group
and group 5 is the enhanced protection group both providing
a method to read and change setpoints. Certain setpoints
are read only or may be restricted in enumerations or ranges
based on trip unit. Each group can be considered an array of
information which can be obtained through Modbus register
access.
Register 3000 is used to send the password and must be
written before initiating a write (function code 6). If a correct
password is written, you must write any new setpoints
within ten seconds. If an incorrect password is written, any
attempt to write a new setpoint will be rejected. Note that
any read of register 3000 will return a random value, not the
password.
Register 3001 is used to select the specific group in which
you are interested. When reading or writing to these regis-
ters, you must first write to register 3001 with the high byte
containing the group number and the low byte equal to 0xFF.
Each table of setpoint register tables include information
on the supported function codes, register number, hex
address, setpoint name, read/write support, and description.
Addresses not listed do not have information available in
them. The description should be referenced to interpret the
format of each register, only the values in the description
field are valid.
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