Installation guide

Estimating Network Performance
890 USE 100 00
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3.5.2 Path Quantities
The following paths are available in the various types of Modbus Plus
devices:
CPU BM85 BP85 SA85/SM85
Data Master 5 4 8 8
Data Slave 4 4 8 8
Program Master 1 4 8 8
Program Slave 1 4 8 8
Data Master Paths in Controllers
Five Data Master paths are provided in controllers. Of these, one path
is reserved for use by the controller’s Modbus port in the bridge mode
between Modbus and Modbus Plus. The remaining four paths are
reserved for use by MSTR functions in the controller’s application
program.
3.5.3 Queueing
If all Data Slave paths are active in a device, incoming transactions
will be queued. Transactions will remain queued until a path is
available, and will then be removed from the queue and given the path.
A final data response is not returned to your application until a full
path is available from origin to destination.
When the destination node removes a transaction from its queue, it
must acquire the token and request the command again from the
originating node. The originator will respond with the command while
the destination has the token. This process occurs automatically,
eliminating the need for polling between the origination and
destination in your application.