behavior of 'write to input register' on AD56xx series

Hi Michael,

To answer your question, the command "Write to Input Register n" writes the data to the input register while the "Update DAC Register n" updates the DAC register n from their respective input registers.

What you have thought of regarding the process is correct. I think that you just overlooked on one function of the part and that is the /LDAC function. Looking back at the part's functional block diagram, the input register comes before the DAC register. The LDAC controls when you are to load the data from the input register to the DAC register.

The command "Write to Input Register n" will write the data on the input register. Depending on the setting of your /LDAC the data will/won't be loaded to the DAC register. I'm guessing your /LDAC pin is tied to low. This would make the command "Write to Input Register n" to immediately load the data to the DAC register without having to execute the command "Update DAC Register n".

You may control the behavior of the /LDAC thru the /LDAC pin or by registers. You may want to take a look at the "/LDAC FUNCTION" sections on page 26 of the Rev.H of the data sheet for details.

I hope I have explained clearly. Please let me know if you have any further questions.

Regards,

Mark

I suspect you are correct. LDAC's pin description is:

"Pulsing this pin low allows any or all DAC registers to be updated if the input registers have new data. This allows all DAC outputs to simultaneously update. Alternatively, this pin can be tied permanently low"

My interpretation was that an edge (ie transition) is needed to initiate the update and not simply a low sig level.  (The other option being the pin could be tied low in which case the use of the LDAC to update the DAC would in effect be disabled.)  Apparently, my interpretation is incorrect.

Thanks for the response and helpful information.