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Hot!reading serial flash SST25VF040B at 50MHz frequency

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san123
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2019/07/19 04:28:31 (permalink)
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reading serial flash SST25VF040B at 50MHz frequency

Hello,
I am using SST25VF040B serial flash as memory for Digital to analog converter on an PCB designed. I have written into serial flash at 8MHz clock rate successfully. Next I tried to read same flash at 50MHz clock rate to provide flash's output as input data to Digital to analog converter. But getting unexpected signals when observed on mixed signal oscilloscope.
Once it read out correct data but after that it started to give some one zero kind of pulse at SO(serial output), even before the command to read flash completes. (though the one zero pattern is observed on flash'SO line i think its not the actual output of flash as when read same address location at much lower rate like 6MHz got corect output).
Also different signals captured on MSO are very noisy.
Not able to understand the behaviour. Please suggest what can be the possible reasons and how to solve it.
 
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    Jim Nickerson
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    Re: reading serial flash SST25VF040B at 50MHz frequency 2019/07/19 11:53:51 (permalink)
    5 (1)
    Maybe this part has problems at the speed you want

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    san123
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    Re: reading serial flash SST25VF040B at 50MHz frequency 2019/07/21 23:55:29 (permalink)
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    Thanks for that information but its datasheet says it support Clock Frequency up to 50MHz(snapshot is attached). And I dont think that its status as "Not Recommended For New Designs" means that it will not support what is being promised in datasheet. 
     
    Also it worked once or twice at that rate. 

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    NKurzman
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    Re: reading serial flash SST25VF040B at 50MHz frequency 2019/07/22 05:54:33 (permalink)
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    Are you sure it is the flash chip and not the cpu? With an SST26 and a PIC32MZ the SPI port need special settings to reach top bus speed.
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    san123
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    Re: reading serial flash SST25VF040B at 50MHz frequency 2019/07/22 22:52:00 (permalink)
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    NKurzman
    Are you sure it is the flash chip and not the cpu? With an SST26 and a PIC32MZ the SPI port need special settings to reach top bus speed.



    Actually I am not using microcontroller SPI port for providing signals to flash. And what kind of setting are required to reach top bus speed??Is it from Microcontroller side that we have to do those setting? because as much I understood from datasheet of the serial flash SST25 is only required to use a different read command for higher(>25MHz) speed operation.
     
     
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