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ADV7842 Recommended for New Designs
The ADV7842 is a dual HDMI 1.4 fast switching rReceiver with 12-Bit, 170 MHz video and graphics digitizer and 3D comb filter decoder. It is a highly flexible...
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ADV7842 on Analog.com

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ADV7842 HPA Operation

		
	
				

			

									
					    MatthewDSE
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Sep 25, 2012 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
		    			
    
			    
    Hello,
    
 
    I am using the port A HDMI input of the ADV7842 and have been unsuccessful in getting the HPA_A (Hot Plug Assert) pin to output a high when 5V is supplied to RXA_5V.  I have been looked through the 5V Cable Detection section and Hot Plug Assert section in the UG-214 guide to help troubleshoot but, can't find the cause of the problem.
    
 

    Here are things I have tested:
    
 
    - I verified the registers mentioned in the Hot Plug Assert section actually matched the default values in the guide. HPA_TRISTATE_A was 0 (pin is active), HPA_AUTO_INT_EDID[1:0] was 01'b, HPA_MAN_VALUE_A was 0'b, etc.
    
 
    - CABLE_DET_A_RAW accurately detects +5V on RXA_5V when a HDMI video source in connected and disconnected.
    
 
    - HPA_STATUS_PORT_A status bit was 1, indicating the chip should have asserted 5V to the pin.  This bit also changed when the video source was connected and disconnected.
    
 
    - The HPA_A pin could not be forced on by setting HPA _MANUAL to 1 and HPA_MAN_VALUE to 1.
    
 
    - Our design has the recommended 1-KOhm resistance between the +5V and HPA.
    
 
    Any suggestions on getting the HPA_A working would be greatly appreciated.
    
 
    Sincerely,
    
 
    Matthew
    
			
    
			
									
		                             
                        

    
    
                                            
                 HDMI/DVI Receivers
                
                                                    
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							FormerMember
					
      
		
      
		    
		    		    
			
				
									FormerMember
							        
			
			
			
    
            
						
                            
            
            				
            
                on Sep 26, 2012 12:47 PM
            
            
						
			            		
    
		
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    Hi Matthew,
    
 
    Some general comments:
    
 
    1) it sounds like you have good I2C access to the part and are reading/writing the registers correctly
    
 
    2) You appear to setting the registers correctly
    
 
    3) Do you have the same problem with port B
    
 
    4) Do you have the same problem with another board
    
 
    5) Have tried to get the pin to work by applying +5V to RXA_5V without the cable connected.  Might lead to cable problems.
    
 
    Other suggestion to look at:
    
 
    1) Manufacturing issues, is the HPA_A pin really connected to the board, i.e. no cold solder joint?
    
 
    2) Is it possible the pin got damaged?  Again try another board or Port B
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
				
						
						
				
				
		
		
    
			
		
    
	
    

    


	

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                on Sep 26, 2012 5:58 PM
            
            
						
			            		
      
		
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      GuenterL,
      
 
      Thank you for the prompt response.  You bring up a good point about trying a different port or board, which I had not done.  So this morning I tried HPA_B but could not get it to output high either however, I may have a lead why. The UG-214 states "the HPA_X pins (where X = A or B) are open drain. An external pull-up resistor is required to pull them high."  Our board does not have a pull-ups on the HPA_X pins.  Are they required for normal operation if +5V is applied to RXA_5V or RXB_5V respectively?  
      
 
      Edit:
      HPA_A has the recommend 1KOhm pull up resistor to RXA_5V, but HPA_B does not.  RXB_5V is tied to 5V because port B is not used on our board.
      
 
      Matthew
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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							FormerMember
					
      
		
      
		    
		    		    
			
				
									FormerMember
							        
			
			
			
            
						
                            
            
            				
            
                on Sep 26, 2012 6:11 PM
            
            
						
			            		
      
		
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      I thought you said you had the 1K resistor between +5 to HPA.
      
 
      The RXA_5V has to have +5V (usually form the source) with a 1k pull up resistor to HPA_A.  The source supplies the voltage to drive the HPA pins through the pull up.
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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                on Sep 26, 2012 6:16 PM
            
            
						
			            		
        
		
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        Sorry, did not edit my message fast enough.  Port A has the pull up, but Port B does not because it is not used in our board.  I may need to try another board as you suggested.
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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                on Oct 3, 2012 6:18 PM
            
            
						
			            		
          
		
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          I believe we found the problem and it was in our design.  We have a front end switch that routes different TMDS video sources (as well as DDC data) to the ADV7842 chip.  The mistake we made was to place the 1KOhm pull-up  in front of the switch instead of the ADV7842.  This would not have been an issue, except the switch pulls the HPA return signal low on the video source side when the HPA signal on the sink side to the ADV is low.
          
 
          Thank you again GuenterL, and I hope this might help others in their design.
          
 

          Matthew
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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							FormerMember
					
          
		
          
		    
		    		    
			
				
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                on Oct 3, 2012 6:32 PM
            
            
						
			            		
          
		
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          Glad you found the problem.  Let me know if you need anymore help.
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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