# Failed Network Communications

Whenever a channel poll fails, for whatever reason, it becomes impossible to determine if that channel is, in reality, violating its alarm violation criteria. Since most network problems are spurious and random, the next poll is likely to succeed. Persistent failures require some sort of notification. The term communications alarm is used to distinguish this situation from alarms based upon alarm violation criteria.

A channel will register a communications alarm violation whenever the following two conditions are met:

1. The channel is configured with an alarm violation criteria (e.g. cannot be set to "status only or disabled").
2. The channel's latency exceeds the Network Communications Alarm Trip Delay Timer.

Once in violation, the communications alarm condition must then persist for the trip delay period before the alarm call sequence begins. The occurrence of a communications alarm tells personnel that there is a persistent network problem preventing access to channel data. It gives absolutely no indication of whether the point is violating the conditions or not. Still, for status reports, alarm calls, LED indicators and acknowledgments, a communications alarm is treated just the same as regular alarms.

Note: The communications alarm trip delay period is not combined with the violation criteria alarm trip delay period. The channel(s) will go into SNA alarm as soon as the communications alarm trip delay period times out.

If any channel configured on a given node is in the communications alarm state, the message depends upon the channel's analog/discrete data type:

CHANNEL TYPE | COMMUNICATION ALARM MESSAGES
--- | ---
Discrete | "Channel <Z> violation SNA Alarm"
Analog / Floating Point | "Channel <Z> reading is NO SCAN DATA SNA Alarm"

To determine the Communications Failure Code with Keycode:

KEYCODE | COMMUNICATION REPORT MESSAGE
--- | ---
915 Z | "Channel <Z.> The present communication status is Error Code xxx" Where Z is the channel number, and xxx is one of the codes in the Diagnostic Codes List.
If all channels configured on a given node are in the communications alarm state the message is simplified to: | "Communication Failure at Node N" Where N is the given node number

To determine the Communications Failure Code with Alarmware:

Connect with Alarmware. The PLC LED should be blinking if there is a detected problem. Click on the blinking LED and the error codes are be listed.

Note: If all channels on a Net are in communications alarm, then in addition to the corresponding channel LEDs being activated, the LED for the Net which it is on will also be activated.