Common Modbus ® Host Configuration - Emerson 5301HxxxxxxxxxxxxxxZZ Series Reference Manual

Rosemount 5300 with HART
April 2019
7. Verify output values as reported by the transmitter.
K.4 Common Modbus
When using Modbus RTU or Modbus ASCII, the registers to receive status and variables
must be configured in the host system.
The transmission of single-precision (4 bytes) IEEE 754 floating point numbers can be
rearranged in different byte orders specified by the Floating Point Format Code. The
format code information, stated for each Remote Terminal Unit (RTU) respectively,
specifies which registers to poll from the Rosemount 5300 Level Transmitter in order for
the RTU to correctly interpret floating point numbers. The byte transmission order for
each format code is demonstrated in
Table K-1: Byte Transmission Order is Specified by the Floating Point Format Code
Format Code
0
1
2
3
Note
Some Modbus hosts cannot read the information described here using Input Registers
(Modbus function code 4). The Input Register information can also be read using Holding
Register (Function code 3). In this case, Input Register number + 5000 is used as Holding
Register number.
Between host system and device, it is recommended to use 60 seconds or less between
polls, and three retries.
K.4.1 Input registers
The register area starting with 1300 can be configured to have any of the four format
codes. The configuration is done by setting FloatingPointFormatCode register (holding
register 3000) to 0-3, as shown in
Rosemount Radar Master program.
Note
Depending on the slave number the Rosemount 5300 Level Transmitter is using, different
registers must be used with the default slave number being 1. Slave number is determined
by the HART address.
476
® ®
to Modbus Converter
®
Byte transmission order
[AB] [CD]
[CD] [AB]
[DC] [BA]
[BA] [DC]
Table
host configuration
Table K-1.
K-1. This configuration can be done with the
Rosemount 5300 Level Transmitter
Reference Manual
00809-0100-4530
Description
Straight word order, most
significant byte first
Inverse word order, most
significant byte first
Inverse word order, least
significant byte first
Straight word order, least
significant byte first