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10.11.6.1 Real-Time Status, Latched Status, and Interrupt Mask Bits
The device has two types of status bits. Real-time status bits are read-only and indicate the state of a signal at the
time it is read. Latched status bits are set when a signal changes state (low-to-high, high-to-low, or both, depending
on the bit) and cleared when written with a logic 1 value. Writing a 0 has no effect. When set, some latched status
bits can cause an interrupt request if enabled to do so by corresponding interrupt enable bits.
Often, but not always, an event-detect latched status bit has a corresponding real-time status bit and a
corresponding interrupt mask bit. For example,
RRTS1.RLOF is the real-time loss-of-frame bit,
RLS1.RLOFD is the
loss-of-frame detect latched status bit, and
RIM1.RLOFD is the interrupt mask.
10.11.6.2 T1 Alarm Criteria
T1 signals have four key alarms: loss-of-signal (LOS), loss of frame (LOF), alarm indication signal (AIS), and
remote alarm indication (RAI).
Table 10-47 lists the set and clear criteria for these conditions.
Table 10-47. T1 Alarm Criteria
ALARM
SET CRITERIA
CLEAR CRITERIA
LOS
192 consecutive zeroes received
14 or more ones received out of 112 possible
bit positions, starting with the first 1 received.
LOF
Two or more errored-frame bits out of
every four, five, or six frame bits.
Fewer than two errored-frame bits out of every
four, five, or six frame bits. (Configured by
AIS (Notes 1, 3)
Four or fewer 0s are received during a
3ms window.
Five or more 0s are received during a 3 ms
window.
SF Bit-2 Mode
(Note 2)
Bit 2 is set to zero in at least 254 of 256
consecutive channel timeslots.
Bit 2 is set to zero in less than 254 of 256
consecutive channel timeslots.
SF 12
th F-Bit Mode
(Note 2)
The 12th framing bit is set to 1 for two
consecutive occurrences.
The 12th framing bit is set to 0 for two
consecutive occurrences.
RAI
ESF Mode
16 consecutive patterns of 0x00FF
appear in the FDL.
14 or fewer patterns of 0x00FF appear in 16
consecutive opportunities in the FDL.
Note 1:
AIS is an unframed all-ones signal. AIS detectors should be able to operate properly in the presence of a 10
-3 error rate and must
not declare AIS in the presence of a framed all-ones signal. The BITS transceiver block has been designed to achieve this
performance.
Note 2:
In SF framing mode, the RAI type is configured by the RSFRAI bit in the
RCR2-T1.RD4RM register. The method of indicating RAI
using the 12th F-Bit in SF mode is also known as Japanese Yellow Alarm.
Note 3:
The following terms are equivalent: AIS = Blue Alarm, RAI = Yellow Alarm, LOS = RCL (receive carrier loss), LOF = Loss of Frame
(previously called RLOS (Rx loss of frame sync) in data sheets for earlier Maxim E1/T1 devices)
10.11.6.3 E1 Alarm Criteria
E1 signals have four key alarms: loss-of-signal (LOS), loss of frame (LOF), alarm indication signal (AIS), and
remote alarm indication (RAI).
Table 10-48 lists the set and clear criteria for these.