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QuadFALC
TM
PEF 22554 E
Functional Description E1
Data Sheet
128
Rev. 1.2, 2006-01-26
4
Functional Description E1
4.1
Receive Path (E1)
An overview of the receive path of one channel of the QuadFALC
special E1 functionalities are described in this chapter.
4.1.1
Receive Line Coding (E1)
The HDB3 line code or the AMI coding is provided for the data received from the ternary or the dual-rail interface.
In case of the optical interface a selection between the NRZ code and the CMI Code (1T2B) with HDB3 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. For NRZ coding, data is latched with the falling edge of signal RCLKI.
The HDB3 code is used along with double violation detection or extended code violation detection (selectable by
FMR0.EXZE)). In AMI code all code violations are detected. The detected errors increment the code violation
counter (16 bits length).
When using the optical interface with NRZ coding, the decoder is bypassed and no code violations are detected.
The signal at the ternary interface is received at both ends of a transformer.
4.1.2
Loss-of-Signal Detection (E1)
There are different definitions for detecting Loss-Of-Signal (LOS) alarms in the ITU-T G.775 and ETS 300233. 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 using 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/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_E). The receive signal level Q is programmable by three
control bits LIM1.RIL(2:0) see Table 142. The number N can be 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. ETS300233
requires detection intervals of at least 1 ms. This time period results always in a LFA (Loss of Frame Alignment)
before a LOS is detected.
Recovery: In general the recovery procedure starts after detecting a logical one (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 defines the number of pulses (1 to 255) to clear the LOS alarm.
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.
4.1.3
Receive Jitter Attenuation Performance (E1)
The jitter attenuator meets the jitter transfer requirements of the ITU-T I.431 and G.735 to 739 (refer to Figure 39)