Schneider Electric 174 CEV - Manual (Page 10)

Modbus Plus to Ethernet Bridge
5
Table 2 Summary of Modbus Data Access Commands
Function Code (Decimal) Command Name
1 Read Discrete Output Status (0xxxx)
2 Read Discrete Input Status (1xxxx)
3 Read Output Register (4xxxx)
4 Read Input Register (3xxxx)
5 Force Single Coil (0xxxx)
6 Preset Single Register (4xxxx)
7 Read Exception Status
8 Subfunction 21 Get/Clear Network Statistics
15 Force Multiple Coils (0xxxx)
16 Preset Multiple Registers (4xxxx)
17 Report Slave ID
Devices which use the Modbus protocol accept incoming requests for data or
statistics. They reply by returning either a normal or an exception response.
The Modbus function code in the request from an originating node always contains
a most significant bit value of 0 (zero). In a normal Modbus response, the function
code of the originating request is echoed, followed by any requested data or
statistics. In an exception response, the most significant bit is set to 1 (one) to
indicate an error, and the next byte contains an exception code showing the
reason for the error.
Table 3 summarizes the Modbus exception codes which may be returned by the
bridge to the originating node. For further information see the Modbus Protocol
Reference Guide , publication PI--MBUS--300.
Table 3 Summary of Modbus Exception Codes
Exception Code (Hexadecimal) Meaning
01 Illegal function
02 Illegal data address
03 Illegal data value
04 Unexpected failure during command execution
05 ACK ---- Requested operation is in progress
06 BUSY ---- Not ready to perform requested operation
07 NAK ---- Requested operation rejected
08 Could not open Modbus Plus path
09 Error during Modbus Plus send
0A Error during Modbus Plus reply