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AD5421 SPI communication issues

		
	
				

			

									
					    rafael
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Sep 23, 2016 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
		    			
    
			    
    Hello,
    
 
    I am having trouble communicating with the AD5421 through SPI.  It seems like I am receiving back the exact same instruction I send to the slave device on every transmission (regardless of whether I am trying to read a register or give a write command) and it happens all in one command (as opposed to happening on the subsequent write command).
    
 
    I am sending 32 bits of data with CRC as the last 8 bits.  My first command is to the control register: 0x02F820EC in which I disable the automatic feedback of the fault register.  When I send this, I receive the exact same message I just sent: 0x02F820EC.
    
 
    I then send a command to read back the control register: 0x8200009C, to which I receive the reply: 0x8200009C.
    
 
    Next, I send a command to the DAC register to output 16mA by sending: 0x01C0005B, and I just receive the exact same message back: 0x01C0005B.  If I measure the current it is held low at the fault value of 3.2mA.
    
 
    Here is a picture of the scope
    
 
    Thanks,
    
 
    Rafael
    
			
    
			
									
		                             
                        

    
    
                                            
                 4-20mA Current Loop D/A Converters
                
                                                    
                 spi
                
                                                    
                 ad5421
                
                                                    
                 Precision D/A Converters
                
                                
            
    
    
    
		
    

							
    
				
				
			
    
					
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                        
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Oct 2, 2016 3:15 PM
            
            
						
			            		
      
		
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      Hi Rafael,
      
 
      Apologies for the delay.
      
 
      Is this only happening when PEC is enabled? Is this also happening when PEC is disabled? What is your working digital supply level? Have you checked if the FAULT pin is asserted? I believe you are using logic analyzer for your digital communications. Could you share the scope shots of the digital lines from an oscilloscope?
      
 
      Regards,
      
 
      Mark
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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                on Oct 6, 2016 5:53 PM
            
            
						
			            		
        
		
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        Hi Mark,
        
 
        Thank you for your reply.  Yes, it happens when the PEC is enabled or disabled.  I am supplying 24VDC from loop+ to loop- and the fault pin does not seem to be high.  Here are the pictures of the scope showing the SIMO and CLK lines, and another showing the SOMI and CS lines.
        
 
        
 
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
						
						
				
				
		
		
        
			
		
        
	
        

        

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