User Guide
Honeywell • 8 BACNET TECHNICAL DATA
3. BACNET TECHNICAL DATA
3.1 BACnet MS/TP protocol
3.2 BACnet IP protocol
3.3 ACD (Address Conflict Detection)
The SmartVFD HVAC/SmartDrive HVAC AC drives implement the ACD algorithm (IETF RFC 
5227). 
The ACD algorithm tries to actively detect if the IP address configured to this device is been 
used by another device in the same network. To accomplish this, ACD sends four ARP request 
packets when the device's Ethernet interface goes up or when its IP address changes. ACD 
prevents the use of the Ethernet interface until the ARP probing finishes. This delays the start-
up of fieldbus protocols about one second. During the delay or after it, the ACD passively 
checks incoming ARP messages for use of the device's IP address. 
If another device with the same IP address is detected, the ACD will try to defend its IP address 
with a single ARP message. If the other device with the same IP address also supports ACD, 
it should stop using the address. If not, the ACD will close the Ethernet connection and indicate 
the situation with an Alarm. This is done according the "DefendWithPolicyB". Acknowledging 
of the Alarm is not possible if the problem is active. ACD opens Ethernet connection if the other 
device with the same IP address disappears from the network. Alarm can be acknowledged 
after this. Other policies are not supported. If the fieldbus protocol has been active, a fieldbus 
fault may be activated (depends on the fieldbus and drive application configuration).
Table 1. 
Connections and 
communications
Interface RS-485
Data transfer method RS-485 MS/TP, half-duplex
Transfer cable STP (Shielded Twisted Pair), type Belden 
9841 or similar
Connector
2.5 mm
2
Electrical isolation Functional
BACnet MS/TP As described in ANSI/ASHRAE Standards 
135-2010 Ver.1 Rev.12
Baud rate 9600, 19200, 38400 and 76800 baud(sup-
ports autobaud detection)
Table 2. 
Connections and 
communications
Interface 100BaseTX, IEEE 802.3 compatible
Data transfer method Ethernet half/full -duplex
Data transfer speed 10/100 MBit/s, autosensing
Protocol BACnet over UDP/IP
Connector Shielded RJ45 connector. 
Cable type CAT5e STP
BACnet IP As described in ANSI/ASHRAE Standards 
135-2010 Ver.1 Rev.12
IP address mode Selectable: Static or DHCP










