there is a black gap at the top of image

Question

Hi expert 
 There is a black gap at the top of image when using a external Signal Generator(NTSC-M) . 
 However,image produced by chips(adv7282m 480P) themselves is 720x480 size is normal. 
 Please refer to the attached file to get detailed description. 
 I hope to get your help,thanks!

ADIApproved · Accepted Answer

Hi Yuanyuan Guo, 
 Do you see this issue with NTSC inputs but not PAL inputs ? 
 If so the issue is probably due to the output format from the ADV728x. 
 By default the ADV728x will output in ITU BT656-3 timing format (this is true for MIPI CSI-2 output models too). 
 If the receiver chip is expecting ITU BT656-4 format then this can result in 10 dark lines appearing at the top of the screen in NTSC mode. This is because ITU BT656-3 format has 10 more lines of vertical blanking than ITU BT656-4 format. 
 
 You can program the ADV728x to output in ITU BT656-4 format. Set User Map, register 0x04 bit[7] to 1. This should solve your issue. 
 
 Regards, 
 Robert Hinchy 
 Senior Applications Engineer, 
 Digital Video Products Group, 
 Analog Devices Inc.)