Emerson 5300, 5400 specifications Common Modbus Host Configuration, Input Registers

Manual Supplement

00809-0500-4530, Rev AA October 2010

Rosemount 5300/5400 Series

COMMON MODBUS HOST CONFIGURATION

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

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 1-12below.

Format	Byte transmission	Description
Code	order
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

Input Registers

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.

1-25