Modbus technical data
vacon • 11
Local contacts: http://drives.danfoss.com/danfoss-drives/local-contacts/
3
Losing one packet is not a big issue because the same request can be sent again after timeout. In
TCP, the packages always reach their destination but if network congestion causes retransmis-
sions, the resent packages will most likely contain old data or instructions when they reach their
destination.
3.4
Connections and wiring
The VACON
®
100 family AC drive supports 10/100Mb speeds in both Full- and Half-duplex modes.
However, real-time process control requires the Full-duplex mode and the 100-megabit speed.
Drives must be connected to the Ethernet network with a Shielded Twisted Pair (STP) CAT-5e cable
(or better). Use only industrial standard components in the network and avoid complex structures
to minimize the length of response time and the amount of incorrect dispatches.
The maximum length of an RS-485 cable depends on the bitrate used, the cable (gauge, capacitance
or characteristic impedance) and the number of devices in the bus. The Modbus RTU specification
states that for a maximum 9600 bits/second bitrate and AWG26 or wider gauge, the maximum
length is 1000 meters. The actual cable length used in an installation can be lower than this number
depending on the aforementioned parameters.
3.5
ACD (Address Conflict Detection) in Ethernet network
The VACON
®
100 family AC drive implements the ACD algorithm (IETF RFC 5227).
The ACD algorithm tries to actively detect if the IP address configured to this device is used by an-
other device in the same network. To accomplish this, the ACD sends four ARP request packets
when the device's Ethernet interface goes up or when its IP address changes. The ACD prevents the
use of the Ethernet interface until the ARP probing finishes. This delays the startup of fieldbus pro-
tocols about one second. During the delay or after it, the ACD passively checks incoming ARP mes-
sages 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 Ether-
net connection and indicate the situation with an Alarm. This is done according the "DefendWith-
PolicyB". Acknowledging of the Alarm is not possible if the problem is active. The ACD opens an
Ethernet connection if the other device with the same IP address disappears from the network. The
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 config-
uration).
The ACD functionality can be enabled and disabled with Duplicate IP Detection panel parameter
(see Chapter 5.3.1 Ethernet common settings (M5.9.1)).
Summary of Contents for 100 INDUSTRIAL
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