CX28344 Conexant, CX28344 Datasheet - Page 98

• Manufacturer Part Number: CX28344
• Description: (CX2834x) Dual / Triple / Quad / Hex / Octal - Enhanced DS3 / E3 Framer
• Manufacturer: Conexant

Functional Description
2.2.7.2
2-52
Normal Message
Writing Messages into the FIFO
Data arriving on the data link channel is automatically written into the FIFO buffer by
the RDL. Type (a1, a2, and b) block description references found below are explained
in
A new data block starts filling up when the RDL detects a transition from flag
sequence (01111110) to stuffed-zero data ( 5 consecutive 1s). Each octet of message
data (i.e., between flag sequences), following stuffed-zero removal (i.e., discarding a
0 directly following five contiguous 1s), is stored in a FIFO byte. A transition from
zero-stuffed data back to flag sequence marks the end of the message and results in an
interrupt with the indication message received.
If the number of data bits collected is not divisible by eight, or if FCS checking is
enabled and the FCS is incorrect, a type (b) block is marked in the block type field of
the data block’s status byte (the first byte of the block), the error type is noted in the
same byte, all the data bytes are discarded, and a new block is started on the byte
following the current status byte. Otherwise, a type (a1) block is marked, the block
length in the status byte is set to the number of data octets stored, and a new block is
started on the byte following the last data byte stored.
Since consecutive messages can share the flag between them, the next message can
start as soon as new zero-stuffed data is detected, regardless of the number of flags
between the messages.
A sequence of five 1s not followed by 0 (i.e., 01111101111110) is faulty and
produces a type (b) block (with alignment error-type).
Aborted Message
A transition from zero-stuffed data to abort sequence ( 7 consecutive 1s) marks an
aborted message and results in an interrupt with the indication message received. A
type (b) block is marked in the block type field, the error type is noted in the same
byte, all the data bytes are discarded, and a new block is started on the byte following
the current status byte. The next message starts only after at least one flag sequence is
located and new zero-stuffed data follows.
NOTE:
NOTE:
Table
2-8.
Mindspeed Technologies™
For each message, all the octets between the initial and terminal flags—not including
the flags but including the FCS—are placed in the FIFO buffer.
Two flags with a shared zero between them are treated as two valid flags.
CX28342/3/4/6/8 Data Sheet
28348-DSH-001-B