Product manual

TAC Xenta Server – Gateway, Technical Manual 10 Using Signals
Schneider Electric Buildings AB, June 2011 85 (184)
04-00124-06-en
10.1.3 Input SNVTs
Input SNVTs are used for collecting information from devices on the
LonWorks network.
An input SNVT can be used in two ways, either as an:
• Update, that is, the SNVT that supplies the value to the input
SNVT decides when to send an updated value,
or
• Poll, that is, the Xenta 913 asks for the signal value at regular
intervals.
The advantage of updating is that network traffic is reduced, since the
value is only sent at a status change: “you get it when it happens”. The
disadvantage is that the programming time is a little longer. When you
add an input SNVT the setting default is Update, that is the Poll check
box is cleared.
When you add a SNVT in XBuilder the following dialog box appears.
The dialog box has a number of controls:
• Name – Input SNVTs are usually called nvi_”XYZ”, to indicate
the direction of the signal, for example nvi_RetAirTemp. A maxi-
mum of 16 characters can be used.
• Type – There are many different types of SNVT. You select the
type you want from the Type list.
• Direction – When you add an input SNVT you set the Direction
to Input.
• Poll – If the Poll check box is not selected the input SNVT
receives a new value when a change is received from the sending
device.
If the Poll check box is selected, the SNVT is updated at the inter-
val specified by the Period (s) value.
• Period (s) – The number you enter in the Period (s) box is the
number of seconds you want to lapse before the Xenta 913 polls
the SNVT. Polling only occurs if the Poll check box is selected.