Product manual

Operating the Model 26
84 025-9158L
Polling
During inactivity the Model 26 polls each Model 6 at the rate set in the Poll Time
parameter (refer to
Poll Time on page 39). As mentioned in the programming section,
there are two philosophies on polling speed, depending on the communication medium
used between the Model 26 and the Model 6s. If the medium is wire line, then it is best to
poll as often and as quickly as possible. If Communication Mode is set to Wire Line, this
is done automatically at 1-second intervals and the poll rate cannot be altered. If the
communication medium is not wire-line, then a slower polling rate is usually desirable.
The user can define a suitable rate in the Software Configuration program.
If the status of a Model 6 is “Off-Line”, the Model 26 will only poll that Model 6 once to
verify it is still “Off-Line”. If the status of a Model 6 is “On-Line” and it fails to respond
when polled, the Model 26 polls that unit four times before changing its status to “Off-
Line”. The time period between polling retries is held in the Retry Period parameter
(refer to
Retry Period on page 43). There is one exception to this. The first time the
Model 26 polls after it is powered up, it will try to communicate with each Model 6 up to
four times before moving on to the next one. This is because all Model 6 statuses are
forced to “Off-Line” to start with.
Every time the Model 26 receives a transmission from a Model 6, it also receives the
complete current status of the Model 6, excluding the state of its relays. The Model 26
uses the received data to immediately update the LEDs associated with that Model 6. If
the Communications Mode is Wire Line (the Model 26 and all Model 6s are set to the
same Communications Mode), a Model 6 will not transmit a change of status until it is
polled. This is why polling time in Wire Line mode is as fast as possible.
If the Communications Mode is not Wire Line, it is usually not desirable for the Model
26 to poll constantly. When a slower polling rate is used, a Model 6 can transmit a status
change to the Model 26 without first being polled. It is important to set the Model 26
polling rate so it does not keep the channel busy for long periods of time.
There are two parameters in the Software Configuration Program associated with polling
rates. They are the Poll Time and Stations Per Poll Time parameters. It is usually
recommended that the Stations Per Poll Time parameter be set to “1”. This allows only
one station to be polled per Poll Time period. That gives any Model 6 needing to transmit
a status change more opportunity for doing so.