DS33R11 Ethernet Mapper with Integrated T1/E1/J1 Transceiver

10.13 G.706 Intermediate CRC-4 Updating (E1 Mode Only)

The device can implement the G.706 CRC-4 recalculation at intermediate path points. When this mode is enabled, the data stream presented at TSERI already has the FAS/NFAS, CRC multiframe alignment word, and CRC-4 checksum in time slot 0. The user can modify the Sa bit positions. This change in data content is used to modify the CRC-4 checksum. This modification, however, does not corrupt any error information the original CRC-4 checksum may contain. In this mode of operation, TSYNC must be configured to multiframe mode. The data at TSERI must be aligned to the TSYNC signal. If TSYNC is an input, then the user must assert TSYNC aligned at the beginning of the multiframe relative to TSERI. If TSYNC is an output, the user must multiframe-align the data presented to TSERI.

Figure 10-4. CRC-4 Recalculate Method

TPOSO/TNEGO

INSERT

EXTRACT

 

 

 

NEW CRC-4

OLD CRC-4

 

 

 

CODE

CODE

 

 

 

 

+

 

 

TSER

 

CRC-4

XOR

MODIFY

 

CALCULATOR

 

Sa BIT

 

 

 

 

 

 

POSITIONS

NEW Sa BIT

DATA

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Maxim DS33R11 specifications 10.13 G.706 Intermediate CRC-4 Updating E1 Mode Only, CRC-4 Recalculate Method