TG > VCO > SDI IP block issue

[Altera_Forum]

I have a simple test design that consist of only three IP blocks. Using Quartus 9.1, and here is the problem I can't figure out what causing it. 

 test1: TG (720x486, 10bit sequence, interlace) >> VCO (preset to ntsc) >> SD SDI = No picture on the sdi monitor !!     test2: TG (1920x1080, 10bit pararell, interlace ) >> VCO (preset to sdi 1080i60) >> HD SDI = Good picture !!     Could somebody in the forum tell me what I did wrong on the TEST1 above? or may be there is bug on the TG for SD SDI?   In fact, on the Test1 above, I have tried to set the TG resolution to 720x480 as well but no luck.    Thanks in advance,   Jimmy

[Altera_Forum]

Test1 does not work because the CVO is expecting F0=244 lines and F1=243 lines in this case. The Test Pattern Generator cannot produce this sequence. You can work around this issue as follows: 

 TG (720x487, 10bit sequence, PROGRESSIVE) >> Interlacer >> VCO (preset to ntsc)

[Altera_Forum]

can you tell me what is VCO?