User manual
905U Wireless I/O Module User Manual
105S Serial I/O Module
Page 26 © October 2001
If communications is still not successful, the “Comms Fail” internal status will be set. In the default
configuration, this will have no consequence and the module will continue to attempt to transmit to the
remote module every ten minutes. For critical applications, the “comms fail” status can be configured
to be reflected to an output on the module for alert purposes. The outputs on the module may also be
configured to reset after a specified timeout (digital outputs reset to “off”, analog outputs reset to 0 mA)
allowing the system to turn off in a controlled manner e.g. a pump will never be left running because of
a system failure.
Repeaters can be used in a system to increase range. Each 905U unit can be configured to act as a
repeater. When configuring an input to be mapped to an output, the communications path to the output
unit, including the repeater addresses is specified. The 905U acts as a store&forward repeater, that is,
the signal is decoded and then retransmitted “as new”.
Example Repeater Communications
Unit A DI 1 mapped to Unit D DO1 via Units B & C
Unit A Unit B
Repeater
Unit C
Repeater
Unit D
• DI 1 is turned
on
• Transmit
• Receive
Acknowledge
• Receive
• Transmit on with
Acknowledge
• Receive
Acknowledge
• Receive
• Transmit on with
Acknowledge
• Receive
Acknowledge
• Receive
• Transmit
acknowledge
• DO 1 is
turned on
3.1.2 Change of state conditions
The module transmits a data message whenever it detects a "change-of-state" on one of its input signals.
A "change-of-state" of a digital or digital internal input is a change from "off" to "on" or vice-versa
provided the change is sustained for 0.5 second (i.e. 0.5 second debounce). The debounce delay is
configurable.
In addition to "change-of-state" transmissions, each module will transmit the status of each input to its
corresponding output every ten minutes (configurable). These updates mean that the outputs are set to
the current input values regularly, even where no “change-of-state” has occurred. These update
transmissions increase the accuracy of the output and give extra system reliability.