DS3161/DS3162/DS3163/DS3164
detecting bytes that mimic flag and escape sequence bytes (7Eh and 7Dh), and replacing the mimic bytes with an
escape sequence (7Dh) followed by the mimic byte exclusive 'OR'ed with 20h. If packet processing is disabled,
stuffing is not performed.
Inter-frame padding inserts start flags, end flags and inter-frame fill between packets. There will be at least one flag
plus a programmable number of additional flags between packets. In octet-aligned mode, the inter-frame fill is
flags. In bit synchronous mode, the inter-frame fill can be flags or all '1's followed by a start flag. If the inter-frame
fill is all '1's, the number of '1's between the end and start flags may not be an integer number of bytes, however,
there will be at least 15 consecutive '1's between the end and start flags. The bit synchronous mode inter-frame
padding type is programmable. If packet processing is disabled, inter-frame padding is not performed.
Packet abort insertion inserts a packet abort sequences as necessary. If a packet abort indication is detected, a
packet abort sequence is inserted and inter-frame padding is done until a packet start flag is detected. In bit
synchronous mode, the abort sequence is FFh. In octet-aligned mode, the abort sequence is 7D7Eh. If packet
processing is disabled, packet abort insertion is not performed.
The packet scrambler is a x
43 + 1 selfsynchronous scrambler that scrambles the entire packet data stream. Packet
scrambling is programmable.
Once all packet processing has been completed, in bit synchronous mode, the 8-bit parallel data stream is
multiplexed into a serial data stream and passed on. In octet-aligned mode, the 8-bit parallel data stream is passed
on.
10.7.6.2 Receive Packet Processor
The Receive Packet Processor performs packet de-scrambling, packet delineation, inter-frame fill filtering, packet
abort detection, destuffing, packet size checking, FCS error monitoring, FCS byte extraction, and bit reordering.
The data coming in can be either a serial data stream or an 8-bit parallel data stream, depending on the framing
mode (see
Table 10-30 for configuration information). The type of data stream received affects packet de-
scrambling, packet delineation, inter-frame fill filtering, packet abort detection, and destuffing, however, it does not
affect packet size checking, FCS error monitoring, FCS byte extraction, or bit reordering. Packet processing can be
disabled (clear-channel enable). Disabling packet processing disables packet delineation, inter-frame fill filtering,
packet abort detection, destuffing, packet size checking, FCS error monitoring, and FCS byte extraction. Only
packet de-scrambling and bit reordering are not disabled.
The packet descrambler is a self-synchronous x
43 + 1 descrambler that descrambles the entire packet data stream.
Packet de-scrambling is programmable. If packet processing is disabled in bit synchronous mode, the serial data
stream is demultiplexed in to an 8-bit data stream before being passed on.
If packet processing is disabled, a packet boundary is arbitrarily chosen, and the data is divided into "packets"
whose size is programmable (maximum packet size setting). These packets are then passed on to bit reordering
bypassing packet delineation, inter-frame fill filtering, packet abort detection, destuffing, packet size checking, FCS
error monitoring, and FCS byte extraction.
Packet delineation determines the packet boundary by identifying a packet start or end flag. Each time slot is
checked for a flag sequence (7Eh). Once a flag is found, it is identified as a start or end flag, and the packet
boundary is set. If packet processing is disabled, packet delineation is not performed.
Inter-frame fill filtering removes the inter-frame fill between packets. When a packet end flag is detected, all data is
discarded until a packet start flag is detected. In bit synchronous mode, the inter-frame fill can be flags or all '1's.
When the interframe fill is all ‘1’s, the number of '1's between the start and end flags does not need to be an integer
number of bytes. In bit synchronous mode when inter-frame fill is flags, there may be only one flag between
packets, or the flags may have a shared zero (011111101111110). In octet-aligned mode, the inter-frame fill can
only be flags, and there may be only one flag between packets. If packet processing is disabled, inter-frame fill
filtering is not performed.
Packet abort detection searches for a packet abort sequence. Between a packet start flag and a packet end flag, if
an abort sequence is detected, the packet is marked with an abort indication, the aborted packet count is
incremented, and all subsequent data is discarded until a packet start flag is detected. In bit synchronous mode,
the abort sequence is seven consecutive ones. In octet-aligned mode, the abort sequence is 7D7Eh. If packet
processing is disabled, packet abort detection is not performed.