Modbus Troubleshooting Tips; Figure 5-73. Exception Code Example For Holding Register Read; Figure 5-74. Diagnostic Function Code - ABB TPU2000 Technical Manual

TPU2000/2000R Modbus/Modbus Plus/ Modbus TCP/IP Automation Guide
SOT

Figure 5-73. Exception Code Example for Holding Register Read

Modbus Troubleshooting Tips

The Modbus Protocol contains a set of commands intended to assist with network troubleshooting. Those
commands are:
08 – Diagnostic Functions
0B –Fetch Communication Event Counter
0C- Fetch Communication Log
The TPU2000 and TPU2000R do support one sub function code of the Diagnostic Function 08.
Commands 0B and 0C are not supported.
Figure 5-74 lists the 08 Diagnostic Function Format.
SOT
Only Sub function 00 is supported. Sub function 00 is the loop-back function. If the sub function hi and lo bytes
are 00 hex, whatever is placed in the data field by the host will be received by the TPU2000 or TPU2000R and
returned or looped back to the host.
Slave Funct. Start Start Regs
Addr. Code Addr Addr Read
03 HI LO HI
Byte 1 ...2........3.......4.......5......6........7....
Modbus Host
Slave Funct.
SOT Addr. Code
83
Error Generated- msb of Function Code Set to 1
Function 08 - Diagnostic Function
Slave Funct. Sub Sub. Data
Addr. Code Funct. Funct.
08 HI LO
Byte 1 ...2........3.......4.......5......6......
Modbus Host

Figure 5-74. Diagnostic Function Code

Regs Error
Check EOT
Read
LO
Modbus Slave Addr =1
Exception
Error
Check EOT
Code
Data Error
EOT
Check
HI LO *
Slave Funct. Sub Sub.
Addr. Code Funct. Funct.
08 HI LO
Network
Partner
V1.0
C
E
Read from
4X Mapping
Modbus Slave Addr =1
E C
Data Data Error
EOT
Check
HI LO *
Modbus
248