detect video Signal

[Altera_Forum]

hello, could someone explain me this following code? i have found it in a demo application but with no Comments. thank you 

 module sigdetect(  oTD_Stable,  iTD_VS,  iTD_HS,  iRST_N );  input iTD_VS; input iTD_HS; input iRST_N; output oTD_Stable;   reg TD_Stable; reg Pre_VS; reg [7:0] Stable_Cont;   assign oTD_Stable = TD_Stable;   always@(posedge iTD_HS or negedge iRST_N) begin  if(!iRST_N)  begin  TD_Stable <= 1'b0;  Stable_Cont <= 4'h0;  Pre_VS <= 1'b0;  end  else  begin  Pre_VS <= iTD_VS;  if(!iTD_VS)  Stable_Cont <= Stable_Cont+1'b1;  else  Stable_Cont <= 0;    if({Pre_VS,iTD_VS}==2'b01)  begin  if(Stable_Cont==9)  TD_Stable <= 1'b1;  else  TD_Stable <= 1'b0;  end  end end

[Altera_Forum]

--- Quote Start ---  hello, could someone explain me this following code? i have found it in a demo application but with no Comments. thank you   module sigdetect(  oTD_Stable,  iTD_VS,  iTD_HS,  iRST_N );  input iTD_VS; input iTD_HS; input iRST_N; output oTD_Stable;   reg TD_Stable; reg Pre_VS; reg [7:0] Stable_Cont;   assign oTD_Stable = TD_Stable;   always@(posedge iTD_HS or negedge iRST_N) begin  if(!iRST_N)  begin  TD_Stable <= 1'b0;  Stable_Cont <= 4'h0;  Pre_VS <= 1'b0;  end  else  begin  Pre_VS <= iTD_VS;  if(!iTD_VS)  Stable_Cont <= Stable_Cont+1'b1;  else  Stable_Cont <= 0;    if({Pre_VS,iTD_VS}==2'b01)  begin  if(Stable_Cont==9)  TD_Stable <= 1'b1;  else  TD_Stable <= 1'b0;  end  end end  --- Quote End ---   module sigdetect (oTD_Stable, iTD_VS, iTD_HS, iRST_N); input iTD_VS; input iTD_HS; input iRST_N; output oTD_Stable; reg TD_Stable; reg Pre_VS; reg Stable_Cont; assign oTD_Stable = TD_Stable; always @ (posedge iTD_HS or negedge iRST_N) begin if (!iRST_N) begin //all reset TD_Stable <= 1 'b0; Stable_Cont <= 4' h0; Pre_VS <= 1 'b0; end else begin //this is for each horisontal syno impulse Pre_VS <= iTD_VS; if(!iTD_VS)Stable_Cont <= Stable_Cont+1' b1; // blank time. Old frame is finish. But new frame is not begun. count HS singal pulses during blank time. else Stable_Cont <= 0;// draw frame. do nothing if ({Pre_VS, iTD_VS} == 2 'b01)// new frame is begin. begin if(Stable_Cont==9) TD_Stable <= 1' b1; // if during blank time been 9 pulses HS the signal is stable. else TD_Stable <= 1 'b0; // signal not stable. end end end   blank time os "back moving beam". I don't know how to in english.

[Altera_Forum]

blank time is http://en.wikipedia.org/wiki/vertical_blanking_interval 

 Sorry for my English.

[Altera_Forum]

--- Quote Start ---  blank time is http://en.wikipedia.org/wiki/vertical_blanking_interval   Sorry for my English.  --- Quote End ---     thank you for your Answer, aber i can't understand why 9 pulse is using

[Altera_Forum]

--- Quote Start ---  thank you for your Answer, aber i can't understand why 9 pulse is using  --- Quote End ---   It's you video signal parameter. You V-blank duration is 9 horizontal sync pulses.

[Altera_Forum]

--- Quote Start ---  It's you video signal parameter. You V-blank duration is 9 horizontal sync pulses.  --- Quote End ---       i cannot find this info that the V-blank is 9 horizontal sync pulses, can you give me more details...thanks

[Altera_Forum]

--- Quote Start ---  i cannot find this info that the V-blank is 9 horizontal sync pulses, can you give me more details...thanks  --- Quote End ---   It's depend on video signal. Different video signal have different parameter. The exactly 9 pulses looks very strange. Usually for video signal specified duration of V-blank, H-blank. And not exactly. You can find parameters for PAL or SECAM or VGA.