In the DS90UB638-Q1, the FPD-Link III receiver transfers incoming video frames to internal video buffers for forwarding to the CSI-2 Transmit ports. When the DS90UB638-Q1 detects an error condition, the standard operation would be to flag this error condition and truncate sending the CSI-2 frame to avoid sending corrupted data downstream. When the DS90UB638-Q1 recovers from an error condition, it will provide Start of Frame and resume sending valid data. Consequently, when the downstream CSI-2 input receives a repeated Start of Frame condition, this will indicate that the data received in between the prior start of frame is suspect, and the signal processor can then discard the suspected data. The settings in registers PORT_CONFIG2 (0x7C) and PORT_PASS_CTL (0x7D) can be used to change how the DS90UB638-Q1 handles errors when passing video frames. The receive port may be configured to qualify the incoming video, providing a status indication and preventing the forward of video frames until certain error-free conditions are met. The Pass indication may be used to prevent forwarding packets to the internal video buffers by setting the PASS_DISCARD_EN bit in the PORT_PASS_CTL register. When this bit is set, video input will be discarded until the Pass signal indicates valid receive data. The receive port will indicate Pass status once specific conditions are met, including a number of valid frames received. Valid frames may include requiring no FPD-Link III parity errors and consistent frame size including video line length and/or number of video lines.

In addition, the receive port may be programmed to truncate video frames containing errors or prevent the forwarding of video until the Pass conditions are met. Register settings in PORT_CONFIG2 register 0x7C can be used to truncate frames on different line/frame sizes or a CSI-2 parity error is detected. When the deserializer truncates frames in cases of different line/frame sizes different line/frame sizes, the video frame will stop immediately with no frame end packet. Often the condition will not be cleared until the next valid frame is received.

The Rx port PASS indication may be used to prevent forwarding packets to the internal video buffers by setting the PASS_DISCARD_EN bit in the PORT_PASS_CTL register 0x7D. When this bit is set, video input will be discarded until the Pass signal indicates valid receive data. The incoming video frames may be truncated based on error conditions or change in video line size or number of lines. These functions are controlled by bits in the PORT_CONFIG2 register. When truncating video frames, the video frame may be truncated after sending any number of video lines. A truncated frame will not send a Frame End packet to the CSI-2 transmit port.