PEB22554 SIEMENS [Siemens Semiconductor Group], PEB22554 Datasheet - Page 70

• Manufacturer Part Number: PEB22554
• Description: ICs for Communications
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

PEB 22554
Functional Description E1
If doubleframe synchronization is consistently present but CRC4 multiframe alignment is
not achieved within 400 ms it is assumed that the distant end is initialized to doubleframe
format. The CRC4 - Non CRC4 interworking is enabled via FMR2.RFS1/0 = 11 and is
activated only if the receiver has lost its synchronization. If doubleframe alignment (basic
frame alignment) is established a 400 ms timer and searching for multiframe alignment
will be started. A research for basic frame alignment will be initiated if the CRC4
multiframe synchronization could not be achieved within 8 ms and will be 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, Sa-, 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 will be 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
will not be changed. Even if multiple basic FAS resynchronizations have been
established during the parallel search, the receiver will be maintained to the initially
determined primary frame alignment signal location.
However, if the CRC4 multiframe alignment could 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 will be chosen. If
necessary, the primary frame alignment signal location will be adjusted according to the
multiframe alignment signal. The CRC4 performance monitoring will be started if
enabled by FMR2.ALMF and the received E-bits will be processed in accordance with
ITU-T G.704.
Switching into the doubleframe format (non CRC4) mode after 400 msec can be disabled
by setting of FMR3.EXTIW. In this mode the QuadFALC continues search for
multiframing. In the interworking mode setting of bit FMR1.AFR is not allowed.
A-Bit Access
If the QuadFALC 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 will be set. With the
deactivation of the remote alarm the interrupt status bit ISR2.RAR is generated.
By setting FMR2.AXRA the QuadFALC 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 will be reset in the outgoing data stream.
Semiconductor Group
70
09.98