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ADG726 communication problem

Question asked by MTJones on Oct 24, 2013
Latest reply on Oct 31, 2013 by MTJones

I have two ADG726 multiplexers, both on separate pcb boards, that I am using to prototype on a bread board.  I only need one multiplexer for my project.  I mention that I have two, only to say that I am experiencing the same issue with each multiplexer, so I don't think I have a defective chip.


I have pins 13 and 14 (both VDD) connected to 5V (measured 4.939V) and pins 23 (GND) and 24 (VSS) connected to ground.  Pins 15-18 (A0-A3) and 21 (WR) are connected to digital I/O pins on my ATmega328 microprocessor.  Pins 18 and 19 (CSA,CSB) are tied together and connected to digital I/O.  Pin 22 (EN) is sometimes tied to ground and sometimes connected to a digital I/O line.  I have no external capacitors or resistors connected. 


My question starts here

I am simply trying to address the switches, but I have made no progress.  For whichever switches I am testing, I have the A switch connected to 5V (I want to test switching inputs near VDD) and the corresponding B switch connected to 3.3V. 


In my code I first write EN low (if it is not tied to ground), then WR low, and next CSA/CSB low (I have tried reversing the order of WR and CSA/CSB).  I then write to A0-A3 in the order A0-A3 (though I have tried reverse order).  I then bring CSA/CSB high and then WR high (I have also reversed the order here, and just left CSA/CSB and WR low). 


Then nothing happens.  I check the output pins 43 (DA) and 41 (DB) and get a ground reading.  This is true for all the switches that I have checked except S16A and S16B.  When I apply my test voltages to S16A/B the outputs will be the same as the corresponding inputs.  However, this is true no matter what I write to A0-A3.  If I have EN connected to an I/O line and I bring it high, the output from S16A/B will go to ground level; otherwise, whatever is connected to S16A/B will be the output no matter the state of WR, CSA/CSB, or A0-A3. 


I assume that I have a communication problem; I can't think of anything else that I am doing wrong.