2.0 Circuit Description
CX28394/28395/28398
2.2 Receiver
Quad/x16/Octal—T1/E1/J1 Framers
2.2.5.1 Loss of Frame
Receive Loss Of Frame (RLOF) is declared when the receive data stream does not
meet the framing criteria specified in the Receiver Configuration register
[RCR0; addr 040].
If the line rate is E1 [T1/E1N; addr 001], RLOF is the logically OR'ed status
of FAS, MFAS, and CAS alignment. These alignments, FRED, MRED and
SRED, respectively, are available separately in the Alarm 3 Status register
[ALM3; addr 049]. Once RLOF is declared the LOF[1:0] bits in ALM3 report the
reason for E1 loss of frame alignment. In T1 mode, RLOF is equal to FRED.
The RLOF real-time status is available in Alarm 1 Status register
[ALM1; addr 047], and the interrupt status is set in the Alarm 1 Interrupt Status
register [ISR7; addr 004]. The RLOF interrupt is enabled by setting RLOF in the
Alarm 1 Interrupt Enable register [IER7; addr 00C].
An FRED count [FRED[3:0]; addr 05A] is also available in the
SEF/LOF/COFA Alarm Counter [AERR; addr 05A]. An interrupt in Counter
Overflow Interrupt Status [ISR4; addr 007] indicates that the FRED counter
overflowed.
While T1 framing mode is enabled, the RLOF status and RLOF interrupt
status are integrated over 2.0 to 2.5 seconds if the RLOF_INTEG bit is set in the
Receive Alarm Signal Configuration register [RALM; addr 045]. The FRED
count is unaffected by RLOF_INTEG.
2.2.5.2 Loss of Signal
If the line rate is T1, the criteria for Receive Loss Of Signal (RLOS) is 100
contiguous zeros (consistent with the standard requirement of 175 ±75 zeros). If
the line rate is E1, the criteria for RLOS is 32 contiguous zeros. RLOS is cleared
upon detecting an average pulse density of at least 12.5% (occurring during a
period of 175 ± 75 bits starting with the receipt of a pulse, and where no
occurrences of 100/32 contiguous zeros are detected). The RLOS real-time status
is available in ALM1, and the interrupt is available in ISR7. The XMTR can be
configured to automatically generate an Alarm Indication Signal (AIS) in the
transmit direction when RLOS is declared (see AUTO_AIS [TALM; addr 075]).
2.2.5.3 Receive Analog
Loss of Signal
RALOS [ALM1; addr 047] can be configured to report loss of receive clock
(RCKI) or loss of receive signal [RLOS; addr 047] for 1 msec depending on the
RALOS configuration bit [RAL_CON; addr 020]. RALOS status is provided for
compatibility with ANSI T1.431 loss of signal detection requirements; and works
in conjunction with LIUs which detect loss of signal if the received signal level
falls below a certain threshold and which have a signal ‘squelch’ feature. If
RAL_CON is set for loss of signal, RALOS indicates that all zeros have been
received for at least 1 msec (RLOS is active for 1 msec). If RAL_CON is set for
loss of clock, RALOS becomes active (1) if the receive clock on the RCKI pin is
not present, and inactive (0) if the clock is present.
2.2.5.4 Alarm
Indication Signal
If the line rate is T1 [T1/E1N; addr 001], the criteria for Receive Alarm Indication
Signal (RAIS) is the reception of four or fewer zeros in a period of 3 ms (4632
bits) and assertion of RLOF. If the line rate is E1, RAIS is set if two consecutive
double frames each contain two or fewer zeros out of 512 bits and FAS alignment
is lost [FRED; addr 049]. The RAIS real-time status is available in ALM1. The
RAIS interrupt is available in ISR7.
2.2.5.5 Yellow Alarm
The criteria for Yellow Alarm (YEL) is described in Table 3-13, Receive Yellow
Alarm Set/Clear Criteria. YEL real-time status is available in ALM1; YEL
interrupt is available in ISR7.
2-8
Conexant
100054E
CONEXANT [ CONEXANT SYSTEMS, INC ]
