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Data Sheet
189
Rev. 1.2, 2006-01-26
QuadFALC
TM
PEF 22554 E
Functional Description T1/J1
the next available framing candidate if there is one. At the same time the internal framing pattern memory is
cleared and other possible framing candidates are lost.
FMR2.MCSP/SSP = 01
B: Synchronization is achieved when 3 consecutive multiframe pattern are correctly
found independent of the occurrence of CRC6 errors. If only one or two consecutive multiframe pattern were
detected the QuadFALC
TM stays in the asynchronous state, searching for a possible additionally available
framing pattern. This procedure is repeated until the framer has found three consecutive multiframe pattern in
a row.
FMR2.MCSP/SSP = 10
B: This mode has been added in order to be able to choose multiple framing pattern
candidates step by step. I.e. if in synchronous state the CRC error counter indicates that the synchronization
might have been based on an alias framing pattern, setting of FMR0.FRS leads to synchronization on the next
candidate available. However, only the previously assumed candidate is discarded in the internal framing
pattern memory. The latter procedure can be repeated until the framer has locked on the right pattern (no
extensive CRC errors). The synchronizer is reset completely and initiates a new frame search, if there is no
multiframing found. In this case bit FRS0.FSRF toggles.
FMR2.MCSP/SSP = 11
B: Synchronization including automatic CRC6 checking Synchronization is achieved
when framing pattern are correctly found and the CRC6 checksum is received without an error. If the CRC6
check failed on the assumed framing pattern the QuadFALC
TM stays in the asynchronous state, searching for
a possible available framing pattern. This procedure is repeated until the framer has locked on the right pattern.
This automatic synchronization mode has been added in order to reduce the microprocessor load.
5.4.6.2
Remote Alarm (yellow alarm) Generation/Detection (T1/J1)
Remote alarm (yellow alarm) is indicated by the periodical pattern “1111 1111 0000 0000 …
B” in the DL-bits (T1
mode, RC0.SJR = 0
B). Remote alarm is declared even in the presence of a bit error rate of up to 10
-3. The alarm
is reset when the yellow alarm pattern no longer is detected.
Depending on bit RC0.SJR = 1
B the QuadFALC
TM generates and detects the remote alarm according to JT G.
704. In the DL-bit position 16 continuous 1 are transmitted if FMR0.SRAF = 0
B and FMR4.XRA = 1B.
5.4.6.3
CRC6 Generation and Checking (T1/J1)
Generation and checking of CRC6 bits transmitted/received in the E(6:1) bit positions is done according to ITU-T
G.706. The CRC6 checking algorithm is enabled by bit FMR1.CRC. If not enabled, all check bits in the transmit
direction are set. In the synchronous state received CRC6 errors are accumulated in a 16-bit error counter and
are additionally indicated by an interrupt status.
CRC6 inversion
If enabled by bit RC0.CRCI, all CRC bits of one outgoing extended multiframe are automatically inverted in case
a CRC error is flagged for the previous received multiframe. Setting the bit RC0.XCRCI inverts the CRC bits before
transmitted to the distant end. This function is logically ored with RC0.CRCI.
CRC6 generation/checking according to JT G.706
Setting of RC0.SJR the QuadFALC
TM generates and checks the CRC6 bits according to JT G.706. The CRC6
checksum is calculated including the FS/DL-bits. In synchronous state CRC6 errors increment an error counter.
5.4.7
72-Frame Multiframe (SLC96 Format, T1/J1)
The 72-multiframe is an alternate use of the FS-bit pattern and is used for carrying data link information. This is
done by stealing some of redundant multiframing bits after the transmission of the 12-bit framing header, see
Table 57. The position of A and B signaling channels (robbed bit signaling) is defined by zero-to-one and one-to-
zero transitions of the FS-bits and is continued when the FS-bits are replaced by the data link bits.
Remote alarm (yellow alarm) is indicated by setting bit 2 to zero in each time slot. An additional use of the D-bits
for alarm indication is user defined and must be done externally.