Emerson 5400 User Manual

00809-0500-4530, Rev AA
October 2010

1-25

Rosemount 5300/5400 Series

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 
5300/5400 transmitter in order for the RTU to correctly interpret floating point 
numbers. The byte transmission order for each format code is demonstrated 
in Table 1-12 below.

Table 1-12.  Byte Transmission 
Order is specified by the Floating 
Point Format Code

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.

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 Table 1-12. This 
configuration can be done with the Rosemount Radar Master program.

NOTE
Depending on the slave number the 5300/5400 transmitter is using, different 
registers must be used with the default slave number being 1. Slave number 
is determined by the HART address.

0

[AB] [CD]

Straight word order, most significant byte first

1

[CD] [AB]

Inverse word order, most significant byte first

2

[DC] [BA]

Inverse word order, least significant byte first

3

[BA] [DC]

Straight word order, least significant byte first