2 Replies Latest reply on Oct 24, 2013 6:32 PM by DaKn_263916

    Noisy read

      Hi everyone,


      I'm a last year student with a question about an issue with CY62148EV30LL-55SXI. On my test card, I can write without problem, but the read operation induces much noise in the circuit.


      First I thought it was a problem with the circuit, so I checked without the memory and circuit works fine, no shorts or wire issues. I'm also following official Cypress guidelines on bypass capacitors.




      Since I'm working on stripboard with adapters, I thought it would be a track length/impedence issue, but since the write and read operation works similarly, I don't really know what's going on.




      My only guess left is that the memory has trouble driving the data line for reading operation (?), whereas the microcontroller has no trouble driving the data line for writing operation.




      What surprises me is that I don't really write/read fast (Instruction clock is at 4MHz => Write at 3,33 kHz, that would be rather slow), the noise induces some errors but with a software verification system, I managed to eliminate most of them. I eliminated all (I need to see with extended test to be sure) errors with lowering alimentation from 3.3V to 3V.




      Speed is not my objective, but this issue (even if I found almost-shamanic workarounds) is still puzzling me and I would like, if possible, advice from a much more experienced person, that would be very nice.




      Another question that may be dumb, but I want to be sure: If I want to use several memories sharing data line and address line, can I keep the others memories in Chip Select enabled, Output/Write disabled while the other one is operating? (I think that yes, but I want confirmation)




      Sorry for the long post, I hope that it makes sense (since English is not my main language)


      Thanks in advance



        • 1. Re: Noisy read

          Would your signal having too slow rising and falling edge?


          What CPU/MCU is your memory connected to?

          • 2. Re: Noisy read

            A scope has a number of capabilities to help -




            1) Ability to look for runt pulses.


            2) Infinite persistance for supply lines to look at worst case pk-pk noise


            and effectiveness of bypassing.


            3) Trigger level to also discriminate a track with excessive L in it.




            When you use caps, look at their ESR vs f curves, not all caps are equal. Also


            polymer tantalums are an order of magnitude better ESR vs f performance vs


            traditional tants. Also consider MLC ceramics along with the tants.




            Regards, Dana.