ProSoft Technology 5204SE-MNET-PDPMV1 - Manual (Page 12)

5204SE-MNET-PDPMV1 ♦ ProLinx Gateway Functional Overview
Modbus TCP/IP to PROFIBUS DP-V1 Pass-Through Master User Manual
Page 12 of 235
ProSoft Technology, Inc.
December 22, 2009
This pass-through capability allows a Modicon processor using its native Modbus
TCP/IP protocol to communicate directly with PROFIBUS DP-V1 slaves and
receive their responses, if any. Pass-through functions bypass the gateway
database, going from Modicon processor to SE MNET Server to PDPMV1
Master to PROFIBUS DP slaves and back.
Note: The normal MNET Server driver will accept and respond normally to remote Modbus TCP/IP
Client requests to read or write data to any address in the gateway's internal database. However,
this special SE implementation of the MNET Server is slightly different.
The SE MNET Server will accept and respond to read requests from Modbus TCP/IP clients in the
same way as the normal MNET Server. However, for write requests, the SE MNET Server will
accept and respond normally only if the address or addresses to be written fall in the gateway
database area designated for PROFIBUS Cyclic Output Data. This area is internal addresses 1000
through 1767, which have corresponding virtual Modbus addresses of 41001 through 41768 (five-
digit addressing) or 401001 through 401768 (six-digit addressing), as shown in the preceding data
flow diagram.
Any write requests received by the special SE MNET Server that are outside this specific data
address range will be rejected by the SE Server and an exception response containing Exception
Code "02 ILLEGAL DATA ADDRESS" will be returned to the requesting Client.
This special modification has been done to preserve the integrity of PROFIBUS Input Data by
preventing external Modbus TCP/IP Clients from writing to and thereby corrupting data in this
critical area, while allowing any Modbus TCP/IP Client to send data to PROFIBUS slaves by writing
it to the PROFIBUS Output Data area.