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18 - External units
The elds under Parameters contain communication and
other settings. The external unit on the right is an expan-
sion module with ve digital outputs. Here, the Address
eld contains the Modbus address used by the device and
the other elds are settings that are sent to the device. You
can link parameters to channels, and if you have done so,
it is the channel that determines which settings are sent to
the device. In this case the values entered here are not the
values that are actually sent to the device.
The elds under Telegram update time specify how fre-
quently various types of message are sent to the external
unit. A telegram is dened as a query/response sequence.
More than one telegram can be dened for an external
unit. The DO module in the example has one telegram to
set the digital outputs and another to write the timeout
and failsafe settings. This is where you specify how often
you want to send each telegram type.
A WMPro running GFBI cannot send more than one
telegram per second to each external unit. You will prob-
ably want to set the digital outputs for the DO module
to update every second. If you also set the Write Settings
telegram to update every second, the WMPro will make
the best of the situation and send the telegram every
other second. This means that the outputs will be updated
every other second. In practice, the values sent using Write
Settings hardly ever change, so you can set the update
frequency to a minute or longer, or even stop updating
altogether once the settings have been changed.
The value in the "Alarm limit com. errors" eld is the maxi-
mum number of failed communication attempts before
the unit is dened as faulty.
Telegram
In GFBI, a telegram is the combina-
tion of a query sent from a WMPro
and a response from an external
unit.
Update time
You can indicate a telegram
frequency for an external unit,
but this cannot be guaranteed.
Communication may slow down
if other units stop working, for ex-
ample, because the WMPro wastes
time waiting for responses that do
not arrive.
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