What Video Output Standard does the ADV7182 Output in Free-Run Mode

Document created by Rob.Analog Employee on May 30, 2013Last modified by Rob.Analog Employee on Mar 24, 2016
Version 5Show Document
  • View in full screen mode

When an analog video source is disconnected from the ADV7182, the ADV7182 will enter free-run mode ( it will output a blue screen or a test pattern).

 

However what video output standard will the ADV7182 output in free-run mode?

 

0) When an analog video source is disconnected from the ADV7182, it will not enter free-run mode immediately. The ADV7182 was designed to be robust to video sources that may not insert sync information. When a source is disconnected ADV7182 will assume the source has forgotten to insert output sync information and the ADV7182 will enter a "coast mode". In "coast mode" the ADV7182 will continue to output noisy video with horizontal and vertical sync information with the same frequency as the last video source.

     The duration of "coast mode" lasts upto a second in normal mode and about 250 ms in fast switch mode.

     a) By setting DEF_VAL_AUTO_EN you can force the ADV7182 to remain in coast mode when a video source is disconnected.

     b) Alternatively you can force the ADV7182 to enter free-run mode immediately by setting the DEF_VAL_EN bit. See "free run" section of the           ADV7182 datasheet for more information.

 

1) When it enters free-run mode the ADV7182 will output in the format of the last valid video source. i.e. if an NTSC source is disconnected from the ADV7182, then the ADV7182 will output in a 480i ITU-656 format in free-run mode.

 

2) If no video source has been connected to the ADV7182, then the ADV7182 will default into outputting in a PAL 576i ITU-656 format in free-run mode.

 

3) This default free-run mode format can be changed by setting the VS_COAST_MODE[1:0] bits ( User Submap, register 0xF9, bits [3:2]). Note that if a video source has been connected to the ADV7182 then the VS_COAST_MODE bits will be ignored. The free-run mode will be the same as the last valid video source connected. (see free-run operation section of the ADV7182 datasheet)

 

4) The user can force the output format output in free-run mode by setting the VID_SEL[3:0] bits (see table 21 of the datasheet). In this case the format last valid video source connected is ignored.

 

5) If the ADV7182 is in free-run mode and a CVBS source is connected then the ADV7182 will try and lock to that source. Once it locks to the CVBS source it will immediately start outputting data from that source. The ADV7182 will not wait until the next field to start outputting data.

 

During this switch over from free-run mode to active video, the ADV7182 can output one field that is nearly twice as long as the standard frame length. This can cause a glitch in some back end processors.

     If deinterlacing is being performed by a frame buffer memory in the backend processor then an algorithm needs to be run to ensure that too long a frame does not cause a buffer overflow event.

Attachments

    Outcomes