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About SPI Clock timing for readback and write

		
	
				

			

									
					    kakashi
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Jul 12, 2024 
				
			
			
		
    
		
		                    	    
    
        	    
    Thread Summary
    
                The user inquires about the AD5781's SPI clock behavior during initialization and operations. The final answer clarifies that the starting clock speed is not predefined and is set by the controller, with a maximum of 35 MHz for writes and 16 MHz for reads. The clock speed must be adjusted accordingly for each operation.
                        	    
    
                
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    Category: Datasheet/Specs
    
    		        		            		    
    Product Number:  AD5781  
    
    		        		    		    
    
		    		    
		    			
    
			    
    I want to use AD5781 in very sophisticated, time-critical project and need your help to understand some things
    

    There is one line in the datasheet which states, "Maximum SCLK frequency is 35 MHz for write mode and 16 MHz for readback mode." on page 5
    

     
    

    Here are the queries i have about the SPI Clock,
    

    1. When the DAC is initialized, what will be the starting clock speed? 16Mhz or 35Mhz
    

    2. If the initial clock frequency is 35 MHz, will it only change to 16 MHz when I use the read command?
    

    3. Will the clock continue to run at 35 MHz while writing? unless the read operation is executed.
    

    Your help will be appreciated
    

    Thank you in advance.
    
			
    
			
									
		                             
                        

    
    
                                            
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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Jul 14, 2024 9:27 PM
            
            
						
			            		
      
		
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      Hi  ,
      

      1.) It does not specify a default or starting clock speed upon initialization in the datasheet but the device itself doesn't set a starting clock speed. The clock frequency is set by the controller device. The 35 MHz (write) and 16 MHz (read) are maximum limits.
      

      2.) The maximum SCLK frequency for the AD5781 is 35 MHz during write operations and 16 MHz during readback operations​. The clock speed should be adjusted to comply.
      

      3.)The clock can continuously run at 35 MHz (max) during write operations. Reduce to 16 MHz for read operations only. These figures mentioned in the datasheet are maximum limits for write/readback operations and are not starting speeds perse, but rather the upper limits that the device can reliably operate at for each type of operation.
      

      Br,
      

      Den
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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    • 
	
      



	
			
		
	



      
	
      
		
      
							
					
      
		
      
		    
		    		    
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Jul 14, 2024 9:27 PM
            
            
						
			            		
      
		
										0
					
	
      

		
		
      
		
      
                                
                                                            
      
					
      Hi  ,
      

      1.) It does not specify a default or starting clock speed upon initialization in the datasheet but the device itself doesn't set a starting clock speed. The clock frequency is set by the controller device. The 35 MHz (write) and 16 MHz (read) are maximum limits.
      

      2.) The maximum SCLK frequency for the AD5781 is 35 MHz during write operations and 16 MHz during readback operations​. The clock speed should be adjusted to comply.
      

      3.)The clock can continuously run at 35 MHz (max) during write operations. Reduce to 16 MHz for read operations only. These figures mentioned in the datasheet are maximum limits for write/readback operations and are not starting speeds perse, but rather the upper limits that the device can reliably operate at for each type of operation.
      

      Br,
      

      Den
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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