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Modbus TCP/IP Driver Manual
Page 16 of 23
// Client Side Map Descriptors where Nodes where Address_Type is PDU
Map_Descriptors
Map_Descriptor_Name
, Data_Array_Name
, Data_Array_Offset
, Function
, Node_Name,
CMD_AO_01
, DA1
, 0
, Rdbc
, Modbus Device2
CMD_AO_02
, DA2
, 0
, Rdbc
, Modbus Device2
CMD_AI_01
, DA3
, 0
, Rdbc
, Modbus Device2
CMD_AI_02
, DA4
, 0
, Rdbc
, Modbus Device2
, Data_Type
, Address
,Scan_Interval
, Float_Reg
, 0
,1.000s
, 32Bit_Reg
, 0
,1.000s
, Input_Float
, 0
,1.000s
, Input_Reg_32Bit
, 0
,1.000s
Each Map Descriptor will read 20 pairs of registers and store them as a 32-bit floating number or a 32-bit
Integer.
If the server device sends swapped registers (low value register first) then use the corresponding _swap
data_types.
NOTE: The value in the address parameter can be ADU, PDU or Modicon 5-digit types; see
Section 5.3.2.
Appendix A.2. Node_Offline_Response
In systems where data is being collected from multiple Server Nodes and made available on a
FieldServer configured as a Modbus TCP/IP Server, when a Server Node goes offline the default
behavior of the FieldServer would be to stop responding to polls for this data. This might not be what the
user wants. Various options exist making it possible to signal that the data quality has gone bad without
creating error conditions in systems sensitive to the default option.
The following options can be configured under the Node parameter, Node_Offline_Response, to set the
response of the FieldServer to the Modbus TCP/IP Client when the Server Node supplying the data is
offline:
No_Response - This is the default option. The FieldServer simply does not respond when the
corresponding Server Node is offline.
Old_Data - The FieldServer responds with the last known data value. This maintains the
communication link in an active state, but may hide the fact that the Server Node is offline.
Zero_Data - The FieldServer responds with the data values set to zero. If the user expects non-
zero values, this option will signal the offline condition without disrupting communications.
FFFF_Data - The FieldServer responds with data values set to FFFF (hex). If the user expects
other values, this option will signal the offline condition without disrupting communications.
When configured as a Server this parameter can force a desired exception response as follows:
Node_Offline_Message or Exception_4 - FieldServer's response will be Exception 4.
Gateway_Path_Unavailable or Exception_A - FieldServer's response will be Exception A.
Gateway_Device_Failed or Exception_B - FieldServer's response will be Exception B.
Example
Nodes
Node_Name
, Node_ID
, Protocol
, Node_Offline_Response
, Port
DEV11
, 11
, Modbus/TCP
, No_Response
, -
DEV12
, 12
, Modbus/TCP
, Old_Data
, -
DEV15
, 15
, Modbus/TCP
, Zero_Data
, -
DEV16
, 16
, Modbus/TCP
, FFFF_Data
, -
DEV17
, 17
, Modbus/TCP
, Exception_4
, -
DEV18
, 18
, Modbus/TCP
, Gateway_Path_Unavailable
, -
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