User manual

MVI56-HART ♦ ControlLogix Platform Reference
HART Multi-drop Master Communication Module User Manual
ProSoft Technology, Inc. Page 95 of 171
October 13, 2011
Multi-drop Mode
Important: If the HART device address is between 1 and 15, you must configure
the channel for multi-drop mode.
If the unit is set for multi-drop mode, the module will poll each unit attached to the
channel starting with polling address 1. The parameter MAX DEVICE COUNT in the
configuration determines the maximum slave address number to be polled in multi-drop
mode. For example, if the MAX DEVICE COUNT parameter is set to 3, the channel will
poll for polling addresses 1, 2, and 3. It is important when assigning the device polling
addresses for instruments on a channel to start with 1 and successfully increase the
value by one until the last instrument is assigned an address. If you set the MAX DEVICE
COUNT parameter to 2, and assign the two instruments addresses 1 and 15, the polling
address 15 will never be used (only addresses 1 and 2). Therefore, the second
instrument will never be polled and will be in communication failure. Up to 15 instruments
can be assigned to a single channel (polling address 1 to 15).