PEF2256 datasheet(89/518 Pages) INFINEON

89 / 518 page

FALC

®56

PEF 2256 H/E

Functional Description E1

User’s Manual

DS1.1, 2003-10-23

Hardware Description

frame alignment) is established, a 400-ms timer and searching for multiframe alignment

are started. A research for basic frame alignment is initiated if the CRC4 multiframe

synchronization cannot be achieved within 8 ms and is started just after the previous

frame alignment signal. The research of the basic frame alignment is done in parallel and

is independent of the synchronization procedure of the primary basic frame alignment

signal. During the parallel search all receiver functions are based on the primary frame

alignment signal, like framing errors, S

a-, Si-, A-bits, …). All subsequent multiframe

searches are associated with each basic framing sequence found during the parallel

search.

If the CRC4 multiframe alignment sequence was not found within the time interval of

400 ms, the receiver is switched into a non-CRC4 mode indicated by setting the bit

FRS0.NMF (No Multiframing Found) and ISR2.T400MS. In this mode checking of CRC

bits is disabled and the received E-bits are forced to low. The transmitter framing format

is not changed. Even if multiple basic FAS resynchronizations have been established

during the parallel search, the receiver is maintained to the initially determined primary

frame alignment signal location.

However, if the CRC4-multiframe alignment can be achieved within the 400 ms time

interval assuming a CRC4-to-CRC4 interworking, then the basic frame alignment

sequence associated to the CRC4 multiframe alignment signal is chosen. If necessary,

the primary frame alignment signal location is adjusted according to the multiframe

alignment signal. The CRC4 performance monitoring is started if enabled by

FMR2.ALMF and the received E-bits are processed in accordance to ITU-T G.704.

Switching into the doubleframe format (non-CRC4) mode after 400 ms can be disabled

by setting of FMR3.EXTIW. In this mode the FALC

®56 continues to search for

multiframing. In the interworking mode setting of bit FMR1.AFR is not allowed.

4.2.3.6

A-Bit Access (E1)

If the FALC

®56 detects a remote alarm indication (bit 2 in TS0 not containing the FAS

word) in the received data stream the interrupt status bit ISR2.RA is set. With the

deactivation of the remote alarm the interrupt status bit ISR2.RAR is generated.

By setting FMR2.AXRA the FALC

®56 automatically transmits the remote alarm bit = 1 in

the outgoing data stream if the receiver detects a loss of frame alignment

(FRS0.LFA = 1). If the receiver is in synchronous state (FRS0.LFA = 0), the remote

alarm bit is reset in the outgoing data stream.

Additionally, if bit FMR3.EXTIW is set and the multiframe synchronous state cannot be

achieved within 400 ms after finding the primary basic framing, the A-bit is transmitted

active high to the remote end until the multiframing is found.

Note: The A-bit can be processed by the system interface. Setting bit TSWM.TRA

enables transparency for the A-bit in transmit direction (refer to Table 19).

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