Abstract: ApplicaTIon Note 338 provides the criteria used to set and clear alarms using the Dallas Semiconductor / Maxim DS2141A T1 Controller and DS2151 Single Chip Transceiver (SCT).
Notes: The definition of Blue Alarm (or Alarm Indication Signal) is an unframed all ones signal. Blue alarm detectors should be able to operate properly in the presence of a 10-3 error rate and they should not falsely trigger on a framed all ones signal. The blue alarm criteria in the DS2141A and DS2151 has been set to achieve this performance.
| Alarm | Set Criteria | Clear Criteria |
| Blue Alarm (AIS) (see note 1 below) | when over a 3ms window, 5 or less zeros are received | when over a 3ms window, 6 or more zeros are received |
| Yellow Alarm | ||
| 1. D4 bit 2 mode (RCR2.2 = 0) | when bit 2 of 256 consecuTIve channels is set to zero for at least 254 occurrences | when bit 2 of 256 consecuTIve channels is set to zero for less than 254 occurrences |
| 2. D4 12th F–bit mode (RCR2.2 = 1; this mode is also referred to as the "Japanese Yellow Alarm") | when the 12th framing bit is set to one for two consecuTIve occurrences | when the 12th framing bit is set to zero for two consecutive occurrences |
| 3. ESF mode | when 16 consecutive patterns of 00FF hex appear in the FDL | when 14 or less patterns of 00FF hex out of 16 possible appear in the FDL |
| Red Alarm (RCL) (this alarm is also referred to as Loss Of Signal) | when 192 consecutive zeros are received | when at least 12.5% ​​one's density is received |
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