Products Mentioned

MAX13488E Production
The MAX13487E/MAX13488E +5V, half-duplex, ±15kV ESD-protected RS-485/RS-422-compatible transceivers feature one driver and one receiver. The MAX13487E...
Datasheet
MAX13488E on Analog.com

MAX13448E Production
The MAX13448E full-duplex RS-485 transceiver features inputs and outputs fault protected up to ±80V (with respect to ground). The device operates from...
Datasheet
MAX13448E on Analog.com

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How to remove received garbage data after sending a packet command.

		            
		

			

									
					    ydiit
					
							


			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Mar 26, 2024 
				
			
			
		
    
		
     
				
		
    
		    		    
		    
		    		      		            		        
    Category: Hardware
    
    		        		            		    
    Product Number:  MAX13488E  
    
    		        		    		    	
			
    i use MAX13488E for connection RS485 temperature sensor.
    

    After sending the data packet, but before receiving the data from the temperature sensor, garbage data is received.
    

    In the circuit, as shown in the attached figure, the MCU and MAX13448E chip are signal-separated.
    

    Is there a circuit problem? Or, I would like to know if there is a way to solve this with software.
    

    Thanks.
    

    

     
    
									
			        
		
    

				
						
        

    
    Tags: 
                                            
                 interface and isolation
                
                                                    
                 hardware
                
                                                    
                 MAX13488E
                
                                                    
                 RS-232 / RS-422 / RS-485 / RS-562
                
                                                    
                 MAX13448E
                
                                        
                                            
                
                
                                        
                                            
                
                
                                
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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Mar 27, 2024 10:30 AM
            
                                    
					
      
	
      

		
		
      
					
      Hello,
      

      I would be happy to help with this.  I have a few questions:
      

      (1) What is the data rate for communication?
      

      (2) You mentioned that junk is received before the reply from the sensor - roughly how much junk data do you read and how long before the sensor reply is received?  If you could, a scope shot of the A, B, ISO_RO and RX2 signals would be really helpful.
      

      (3) I don't see a differential termination in your schematic - is there one?  If so, what is the value?
      

      Overall, your circuit looks OK, but I do have some suggestions: while the pull-up/-down resistor values for this part are not specified, higher value impedances will take longer to pull the lines high or low.  If it is possible in your circuit, I would recommend reducing these values to something like 1kohm or less.  Additionally, there is a condition where the RO output on the MAX13488E can go high impedance during switching (see the Function Tables on page 11 of the datasheet).  I don't see a pull-up on the RO output on your schematic, but here I would recommend a weak pull-up (something like 10k) to ensure the RO state for conditions where the part could take an extended time switching between a driver enable and receive enable state.
      

      Thanks,
      

      Shasta
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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