R8075

The R8075 has the following features including CRC-4 transmit and receive as per CCIIT Recommendation 6.704;Insertion and extraction of Spare Bits (SP1 and SP2);Independent error detection and reporting of CRC-4 and multiframe alignment errors;CRC-4 enable/disable capability;Enhanced HDB3 encode/decode section, includes reporting of bipolar violations;Read/Write access to International Bits in CRC-4 disable mode (through 88070).

The Rockwell 88075 CRC-4 Encoder/Decoder is a support device to the R8070/R8070A T-1/CEPT PCM Transceiver and the 88069 Line Interface Unit. Used with the 88070 and the 88069, the 88075 implements transmit and receive functions in accordance with CCITT Recommendation 6.704 for PCM30 using CRC-4. Operation of the 88075 is entirely transparent other than error detection/reporting and handling of the Spare Bits. The 88075 can be set in either enable or disable mode, for systems which handle both data encoded with CRC-4 and without CRC-4.Transmit functions compute the CRC-4 polynomial and insert the proper alignment timing and Spare Bits (SP1,SP2) into the transmit data stream. HDB3 encoding is also handled by the 88075.Receive functions are independent error detection of CRC-4 and multiframe alignment, extraction of the spare bits, and HDB3 decoding (including reporting of bipolar violations).The Bit, Channel and Frame timing signals are available to the system for both the transmit and receive sections.The 88075 can support ISDN applications using the 88070 256N mode and PCM30 signalling modes using the 256S mode.

The 88075 is used with the 88070 Transceiver and the 88069 Line Interface Unit to provide CRC-4 capability for PCM30 systems. There are two basic sections to the 88075: the Transmit section and the Receive section Signals connected to either the 88069 or 88070 are described in the pin definitions (Table 2). For more information, please refer to the functional and interface descriptions of the data sheets for the 88069 and 88070.The transmit section computes the CRC-4 polynomial,inserts alignment timing signals and spare bits into the transmit data stream, and encodes the bipolar transmit data using HDB3.