ProSoft Technology PS-QS-1x10-0781 - Manual (Page 16)

FieldServer Configuration Manual Page 16 of 90
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4 MAP DESCRIPTOR FUNCTIONS 4
Map Descriptor functions determine how data is mapped between Data Arrays and the corresponding driver data
points. The choice of function used is critical in ensuring that the right relationship is established with the device
being communicated with. The most important decision to make when choosing a function is whether the
function needs to be active or passive. Once this is determined, the trigger for initiating communications
determines which active or passive function is used.
4.1 Active vs. Passive functions
Active functions control the communications activity for the associated points in the network. Specifying an active
function for a point will enable the FieldServer to decide when a point is updated, and monitor the health of the
communications path for that point (if the associated protocol allows for this). Specifying a passive function will
mean that the FieldServer expects the communications for that point to be controlled and monitored by another
device on the associated network.
Note: By design, it is necessary that all active Map Descriptors communicate to a point that has a passive mapping
on the remote device, and that passive Map Descriptors are controlled by an active mapping on the remote device.
There is a loose relationship between Active/Passive and Client/Server. Clients usually use active mappings and
Servers usually use passive mappings, however Active Servers and Passive Clients do exist. Points that send an
update to a network on change (e.g.: Alarm panels) are a good example of Active Servers.
Another set of terminology used in this area is solicited vs. unsolicited messages. A Client receives a solicited
message from a Server when it asks for it (i.e.: the point is polled). A Client receives an unsolicited message from a
Server when the Server sends the point without the Client asking for it. Clients that send solicited messages are
Active Clients communicating with Passive Servers. Clients that receive unsolicited messages are Passive Clients
communicating with Active Servers.
4.2 Passive Map Descriptor Functions
4.2.1 Passive
The Passive function will not initiate any communications but waits to be solicited by a remote device and
responds with data accordingly. The Passive function will also accept writes and update the associated Data Array.
4.2.2 Passive Client (Passive_Client)
The Passive_Client function is intended for use where the associated Map Descriptor performs a Client function
and is connected to an active Server. The Passive_Client function will consume all unsolicited messages for the
related point/s and store them in the associated Data Array.
4 Note that not all functions are supported by all drivers. Refer to the specific Driver Manual for information on functions supported by
individual drivers.