Functional Overview 5204SE-MNET-PDPMV1 ♦ ProLinx Gateway
User Manual Modbus TCP/IP to PROFIBUS DP-V1 Pass-Through Master
ProSoft Technology, Inc. Page 15 of 235
December 22, 2009
2 In order for the processor to 'see' any of the data being received from the
PROFIBUS slaves or to send any data to the PROFIBUS slaves, your control
and sequencing logic must initiate Modbus TCP/IP Client command
messages from the processor to the gateway by using the binary trigger
variables provided for each DFB. This requirement applies equally for the
cyclic DFBs and for the acyclic DFBs. The main difference will be that the
DFBs to update cyclic data will most likely be triggered much more often than
the acyclic DFBs are triggered. For additional details, see Sample Control
and Sequencing Logic for Cyclic Data Polling (page 113).
3 The basic communication cycle between the processor and the gateway is:
o User-created logic in the processor sends a Modbus TCP/IP command
message to the gateway by triggering one of the fourteen (14) provided
DFBs.
o The MNET Server driver on the gateway receives the command.
o The MNET Server driver processes the command.
o The MNET Server driver returns a Modbus TCP/IP response to the
processor.
o Some commands cause data to be returned, such as read commands.
Some commands, such as write commands, return only an
acknowledgement that the command was received and executed.
Commands sometimes fail. Any data or error response to a command
returned by the MNET Server will be available in the provided Variables or
DDTs after being placed there by the triggered DFB that initiated the
process cycle. User-created logic in the processor must process data or
errors received in the Modbus TCP/IP response, if any.
o If no Modbus TCP/IP response is received within the time value specified
in a Timeout variable, the triggered DFB will set a Message Error bit flag
to indicate the message sequence failed and should be retried by
triggering a new message cycle.
4 In cases where PROFIBUS cyclic I/O data, general gateway status, or
standard PROFIBUS slave diagnostic data are concerned, these read or
write requests from the processor are handled internally in the gateway and
are processed asynchronously from any PROFIBUS DP Master processes
that might also be running in the gateway. This means these cyclic requests
tend to be responded to much more quickly than requests involving acyclic
messages that must be "passed-through" to the PROFIBUS Master for
execution before a Modbus TCP/IP response can be created and returned to
the processor.
5 In cases where PROFIBUS DP-V1 acyclic messages are concerned, these
read or write requests require a longer, more involved process cycle,
synchronized with actions on the PROFIBUS DP-V1 Master side of the
module. When the processor sends a Modbus TCP/IP read or write request,
using an acyclic message DFB:
o User-created logic in the processor sends a Modbus TCP/IP command
message containing the data needed for the PROFIBUS DP-V1 acyclic
message to the gateway by triggering one of the ten (10) provided acyclic
DFBs.
o The gateway MNET Server must process the incoming command.