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SN74LV815AN counter problem

Oto Meran
Prodigy 20 points

Hello,

we are using counter SN74LV815AN with 25Mhz input  as 32bit  counter.

 

when i read with frequency for example 4khz, and clear counter after each reading, everything is OK

i receive numbers from couter: 0x184D; 0x184C; 0x184B; 0x184C etc. which match 25000000 : 4000 = 6250 = 0x186A

 

but when i read with frequency 6060Hz

i receive numbers from counter: 0x0FFF; 0x1001; 0x0FFE; 0x1002 and sometimes 0x0000

this hapenned, only on frequncies 6060Hz or 3040Hz, maybe on others. around counter values 0x1000(6060Hz) and 0x2000(6060Hz)

 

Does anybody knows, what does it means?

Thank you for your suggestions.

 

Oto Meran

 

 

 

 

 

 

  • 0
    Prodigy 20 points

    Hello,

    do you disable the count frequency when you read out the counter? I've made the experience, that I have to stop the count clock (with an external gate i.e.), then transfer the counting result in the output register, then you can clear the counter and read out the result. I use the same counter but in the way of 2 16 bit counter. In the beginning I have had a similar problem.

    Perhaps this is a hint for you.

    Amelie Prinz 

  • 0 in reply to Amelie Prinz
    Prodigy 20 points

    Hello,

     

    thank you for your reply.

     

    You are right. I read datasheet again and I probably broke the condition CLKA 10ns before RCLK

    Unfortunately, i havent ext. gate on counter input, so i must choose another solution.

     

    Thanks again.

     

    Oto Meran