Modbus Interface; Modbus Register / Word Ordering; Register Mappings - Badger Meter ER-500 Programming Manual

MODBUS INTERFACE

A subset of the standard Modbus commands is implemented to provide access into the data and status of the ER-500
monitor The following Modbus commands are implemented:
Command
01
03
05
Type
Long Integer
Single Precision IEEE754

Modbus Register / Word Ordering

Each Modbus holding register represents a 16-bit integer value (2 bytes) The official Modbus standard defines Modbus as a
'big-endian' protocol where the most significant byte of a 16-bit value is sent before the least significant byte For example,
the 16-bit hex value of '1234' is transferred as '12' '34'
Beyond 16-bit values, the protocol itself does not specify how 32-bit (or larger) numbers that span over multiple registers
should be handled It is very common to transfer 32-bit values as pairs of two consecutive 16-bit registers in little-endian word
order For example, the 32-bit hex value of '12345678' is transferred as '56' '78' '12' '34' Notice the Register Bytes are still sent in
big-endian order per the Modbus protocol, but the Registers are sent in little-endian order
Other manufacturers store and transfer the Modbus Registers in big-endian word order For example, the 32-bit hex value
of '12345678' is transferred as '12' '34' '56' '78' It does not matter which order the words are sent, as long as the receiving
device knows which way to expect it Since word order is a common problem between devices, many Modbus master
devices have a configuration setting for interpreting data (over multiple registers) as 'little-endian' or 'big-endian' word order
This is also referred to as swapped or word swapped values and allows the master device to work with slave devices from
different manufacturers
If the endianness is not a configurable option within the Modbus master device, it's important to make sure it matches
the slave endianess for proper data interpretation The ER-500 monitor actually provides two Modbus register maps to
accommodate both formats This is useful in applications where the Modbus master cannot be configured for endianness

Register Mappings

Data Component
Name
Spare
Flow Rate
Spare
Positive Totalizer
Grand Total Totalizer
Battery Voltage
Spare
For reference: If the ER-500 totalizer = 12345678 hex
Register 40106 would contain 5678 hex (Word Low)
Register 40107 would contain 1234 hex (Word High)
February 2017
Bits
32
32
MODBUS Registers
Long Integer Single Precision
Format Floating Point Format
40100...40101
40102...40103
40104...40105
40106...40107
40108...40109
40110...40111
40112...40113
DSY-PM-00028-EN-02
Description
Read Holding Registers
Force Single Coil
Bytes
4
4
40200...40201
40202...40203
Gallons, Liters, MGallons, Cubic Feet, Cubic Meters, Acre
Feet, Oil Barrel, Liquid Barrel, Feet, Meters, Lb, Kg, BTU,
40204...40205
40206...40207
40208...40209
40210...40211
40212...40213
Read Coils
Modbus Registers
Available Units
—
MBTU, MMBTU, TON
Per
Second, Minute, Hour, Day
x xx
—
Modbus Interface
2
2
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