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Data Sheet
169
Rev. 1.2, 2006-01-26
QuadFALC
TM
PEF 22554 E
Functional Description T1/J1
5
Functional Description T1/J1
5.1
Receive Path in T1/J1 Mode
An overview about the receive path of one channel of the QuadFALC
special T1/J1 functionalities are described in this chapter
5.1.1
Receive Line Coding (T1/J1)
The B8ZS line code or the AMI (ZCS, zero code suppression) coding is provided for the data received from the
ternary or the dual-rail interface. All code violations that do not correspond to zero substitution rules are detected.
The detected errors increment the code violation counter (16 bits length). In case of the optical interface a
selection between the NRZ code and the CMI Code (1T2B) with B8ZS or AMI postprocessing is provided. If CMI
code is selected the receive route clock is recovered from the data stream. The CMI decoder does not correct any
errors. In case of NRZ coding data is latched with the falling edge RCLKI.
When using the optical interface with NRZ coding, the decoder is bypassed and no code violations are detected.
Additionally, the receive line interface contains the alarm detection for Alarm Indication Signal AIS (Blue Alarm)
and the loss-of-signal LOS (Red Alarm).
The signal at the ternary interface is received at both ends of a transformer.
5.1.2
Loss-of-Signal Detection (T1/J1)
There are different definitions for detecting Loss-Of-Signal alarms (LOS) in the ITU-T G.775 and AT&T TR 54016.
The QuadFALC
TM covers all these standards. The LOS indication is performed by generating an interrupt (if not
masked) and activating a status bit. Additionally a LOS status change interrupt is programmable by register
GCR.SCI.
Detection: An alarm is generated if the incoming data stream has no pulses (no transitions) for a certain
number (N) of consecutive pulse periods. “No pulse” in the digital receive interface means a logical zero on
pins RDIP/RDIN or ROID. A pulse with an amplitude less than Q dB below nominal is the criteria for “no pulse”
in the analog receive interface (LIM1.DRS = 0) (LIM1_T). The receive signal level Q is programmable by three
control bits LIM1.RIL(2:0), see Table 142. The number N is set by an 8-bit register (PCD). The contents of the
PCD register is multiplied by 16, which results in the number of pulse periods, i.e. the time which has to
suspend until the alarm has to be detected. The programmable range is 16 to 4096 pulse periods.
Recovery: In general the recovery procedure starts after detecting a logical 1 (digital receive interface) or a
pulse (analog receive interface) with an amplitude more than Q dB (defined by LIM1.RIL(2:0)) of the nominal
pulse. The value in the 8-bit register PCR (PCR_T) defines the number of pulses (1 to 255) to clear the LOS
alarm. Additional recovery conditions are programmed by register LIM2.
If a loss-of-signal condition is detected in long-haul mode, the data stream can optionally be cleared automatically
to avoid bit errors before LOS is indicated. The selection is done by LIM1.CLOS = 1.
5.1.3
Receive Jitter Attenuation Performance (T1/J1)
The jitter attenuator meets the jitter transfer requirements of the PUB 62411, PUB 43802, TR-TSY 009,TR-
TSY 253, TR-TSY 499 and ITU-T I.431 and G.703 (refer to Figure 64).