
XRT84L38
318
OCTAL T1/E1/J1 FRAMER
REV. 1.0.1
In DS1 mode, different framing formats are distinguished by different patterns and functions of the framing
alignment bit (first bit of a DS1 frame). The XRT84L38 can generate the framing alignment bits internally
according to a particular framing format.
At the same time, the users can generate the framing alignment bits externally and insert them into the framer
through the Transmit Serial Data Input Interface block via the TxSer_n pin. It is the user's responsibility to
maintain the accuracy and integrity of the framing alignment bits. The user also has to make sure that the
framing alignment bits are inserted into the framer at right position and right timing. However, this option is only
available when the XRT84L38 is configured to run at a normal back-plane rate of 1.544Mbit/s.
The Framing Bit Source Select bit of the Synchronization MUX Register (SMR) controls source of the framing
alignment bit. The table below shows configurations of the Framing Bit Source Select bit of the Synchronization
MUX Register (SMR).
SYNCHRONIZATION MUX REGISTER (SMR) (INDIRECT ADDRESS = 0XN0H, 0X09H)
9.2.2
How to configure the framer to input CRC-6 bits from different sources
If the framer is configured to operate in Extended Super-frame Format, the framing bits of Frame number 2, 6,
10, 14, 18 and 22 of an ESF multi-frame are used as Cyclic Redundancy Check (CRC-6) code of the last ESF
multi-frame. The CRC-6 bits are an indicator of the link quality and could be monitored by the user to establish
error performance report.
The XRT84L38 can generate the CRC-6 bits internally by calculating the CRC check-sum of all the 4,632 bits
in DS1 multi-frame while assuming the framing bits to be one.
At the same time, the users can generate the CRC-6 bits externally and insert them into the framer through the
Transmit Serial Data Input Interface block via the TxSer_n pin. It is the user's responsibility to correctly
compute the CRC-6 bits according to DS1 algorithm. Also, the user has to make sure that the CRC-6 bits are
inserted into the framer at right position and right timing. However, this option is only available when the
XRT84L38 is configured to run at a normal back-plane rate of 1.544Mbit/s.
B
IT
N
UMBER
B
IT
N
AME
B
IT
T
YPE
B
IT
D
ESCRIPTION
0
Framing Bit Source
R/W
Framing Bit Source:
This READ/WRITE bit-field permits the user to determine where the fram-
ing alignment bits should be inserted.
0 - The framing alignment bits are generated and inserted by the framer
internally.
1 - If the framer is operating in normal 1.544Mbit/s mode, the framing align-
ment bits are passed through from the Transmit Serial Data Input Interface
block via the TxSer_n pin.