Modbus RTU Function Codes 
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Register Address Structure 
Table 9-1  Integer Parameter Type 
Register 
Numbers 
(Dec) 
Name  Access  Notes 
1  Type = 1  NOT SUPPORTED  16-bit Unsigned Integer 
2  Attribute  NOT SUPPORTED  1 = Read Only, 
2 = Read/Write 
3  Value (16 bit integer)  Read / Write   
4  Not Used  NOT SUPPORTED   
5  Low Range (16 bit integer)  NOT SUPPORTED   
6  Not Used  NOT SUPPORTED   
7  High Range (16 bit Integer)  NOT SUPPORTED   
8  Not Used  NOT SUPPORTED   
9 to 13  Description Text (ASCII string)  NOT SUPPORTED   
 
Table 9-2  Floating Point Parameter Type 
Register 
Numbers 
(Dec) 
Name  Access  Notes 
1  Type = 2  NOT SUPPORTED  IEEE Floating Point 
2  Attribute  NOT SUPPORTED  1 = Read Only,  
2 = Read/Write 
3  Value (float high word)  Read / Write   
4  Value (float low word)  NOT SUPPORTED   
5  Low Range (float high word)  NOT SUPPORTED   
6  Low Range (float low word)  NOT SUPPORTED   
7  High Range (float high word)  NOT SUPPORTED   
8  High Range (float low word)  NOT SUPPORTED   
9 to 13  Description Text (ASCII string)  NOT SUPPORTED   
 
Register Count 
The register count depends on the data format of the registers being read or written. 
Integer data is represented in sixteen bits and is transferred high byte first. 
Floating point data is transferred in IEEE 32-bit format. 
The register count definitions are: 
  0001 = Integer Data 
  0002 = Floating Point Data