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CAN-FD



		

			

									
					    xiasigang
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Aug 18, 2024 
				
			
			
		
    

				
		
    
		    		    
		    
		    		      		            		        
    Category: Hardware
    
    		        		            		    
    Product Number:  ADM3055 
    
    		        		    		    	
			
    Hi
    

    My two devices using ADM3055 form CAN-FD communication, with one device's CAN-FD ground connected to RS232 ground. RS232 sends data in 1-second cycles.
    

    I used an oscilloscope to measure CAN-H and CAN-GND and obtained the following curves.
    

     
    

    

    

    

    

    

    

    

    Can this curve indicate that RS232 caused CAN communication failure？But when I measured CAN-H and CAN-L, I didn't see the impact of RS232. Can RS232 GND be connected to CAN-FD GND？
    

     
    
									
			        
		
    

				
						
        

    
    Tags: 
                                            
                 interface and isolation
                
                                                    
                 CANFD
                
                                                    
                 hardware
                
                                                    
                 rs232
                
                                                    
                 ADM3055
                
                                
            
    
    
    

		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    
















    
	
    
	
    
					



			


				
	









	
      
	

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													+1
							
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Aug 19, 2024 11:51 AM
            
            
					
      
	
      

		
		
      
					
      Hi Xiasigang,
      

        Unfortunately, I don't have enough details about your system to understand what is being shown in the oscilloscope plots or really make an informed guess about what might be the problem.  
      

        My understanding is that your system has both CAN and RS-232 ports, that at least the CAN port is isolated and you've connected the CAN port's isolated "GND"/reference to the GND reference for the RS-232 port.  Furthermore, it appears that there are issues with CAN communications following RS-232 data transmissions.
      

        Its possible that it is an electrical hardware issue or it could be software based (e.g. the RS-232 driver/ISR clobbers the CAN driver/ISR in some manner).
      

        Because RS-232 is single-ended, it is conceivable that when you connected the two port's references together the RS-232 signaling is inducing some common mode voltage onto the CAN bus which might exceed the common mode voltage range.  The ADM3055's common mode voltage range on the receiver is +/-25V which is larger that the RS-232 signaling max levels (+/-15), so I'd think it wouldn't be an issue, but...   Depending on the wiring layout there could also be some common mode to differential conversion (e.g. more coupling from RS-232 to CANH or CANL) which could then introduce interference in the CAN bus without reaching the common mode voltage limits.
      

        Normally, I'd caution against connecting the gnd/reference of these ports together, but how the references for interface ports are connected is a really a greater system level architecture question. Different systems can have different preferred connection schemes.
      

      Eric
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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