Maxim Integrated DS21Q55 - Manual (Page 56)

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9.2 Automatic Alarm Generation
The device can be programmed to automatically transmit AIS or remote alarm. When automatic AIS
generation is enabled (E1TCR2.1 = 1), the device monitors the receive side framer to determine if any of
the following conditions are present: loss of receive frame synchronization, AIS alarm (all ones)
reception, or loss of receive carrier (or signal). If any one (or more) of the above conditions is present,
then the framer will either force an AIS or remote alarm.
When automatic RAI generation is enabled (E1TCR2.0 = 1), the framer monitors the receive side to
determine if any of the following cond itions are present: loss of receive frame synchronization, AIS alarm
(all ones) reception, or loss of receive carrier (or signal) or if CRC4 multiframe synchronization cannot be
found within 128ms of FAS synchronization (if CRC4 is enabled). If any one (or more) of the above
conditions is present, then the framer will transmit a RAI alarm. RAI generation conforms to ETS 300
011 specifications and a constant remote alarm will be transmitted if the DS21Q55 cannot find CRC4
multiframe synchronization within 400ms as per G.706.
Note: It is an illegal state to have both automatic AIS generation and automatic remote alarm generation
enabled at the same time.