7.3.20.2 Forward Channel and Back Channel Error Checking

While in BIST mode, the serializer stops sampling the FPD-Link input pins and switches over to an internal all-zeroes pattern. The internal all-zeroes pattern goes through the scrambler, DC-balancing, and so forth and is transmitted over the serial link to the deserializer. The deserializer, on locking to the serial stream, compares the recovered serial stream with all-zeroes and records any errors in status registers. Errors are also dynamically reported on the PASS pin of the deserializer.

The back-channel data is checked for CRC errors once the serializer locks onto the back-channel serial stream, as indicated by link detect status (register bit 0x0C[0] - Table 10). CRC errors are recorded in an 8-bit register in the deserializer. The register is cleared when the serializer enters BIST mode. As soon as the serializer enters BIST mode, the functional mode CRC register starts recording any back channel CRC errors. The BIST mode CRC error register is active in BIST mode only, and the register keeps a record of the last BIST run until the register is cleared or the serializer enters BIST mode again.

Figure 19. BIST Waveforms, in Conjunction With Deserializer Signals