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Altera_Forum's avatar
Altera_Forum
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13 years ago

detecting rising and falling edge

Hello.

I have an Enitiy that have in siraial input ,clk and output bus.

i need to count time between falling edge of my input until rising edge of the same input but all this needs to be synchronize to main cl k.

Thx

1 Reply

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    13 years ago

    Here's what you need to do;

    1) Route your serial clock through a dual-DFF synchronizer that is clocked by your main clock. Lets say the input is called sclk, and the output is called sclk_sync.

    2) Route sclk_sync through another DFF, and call that sclk_dly.

    3) Draw yourself a timing diagram of sclk_sync and sclk_dly. What logic operation do you need to detect the rising edge and falling edge? Hint, what does 'sclk_sync and sclk_dly' look like, how about 'sclk_sync and not sclk_dly'? One combination will give you the rising-edge, while another will give you the falling-edge.

    4) Create logic to enable/disable a counter clocked by clk, where the enable/disable logic is based on the rising-edge/falling-edge logic.

    Try to figure the logic out. If you get stuck, ask for help.

    Cheers,

    Dave