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Altera_Forum
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15 years ago

Problems on Cyclone's reset value

Problems on Cyclone's reset valueHi all,I'm currently using Cyclone EP1C6T144C8 in my design and having some problems with the usage of reset, hope someone may help me out with it:)The problem occurs when I implemented a simple counter in FPGA. It's just a typical working on clock and reset, but the "reset" may or may not put the counter to the expected value.Case 1, if I reset the counter to all-0s://--reg [3:0] cnt;always@(posedge rst or posedeg clk)if(rst) cnt

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  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    It's a very basic logic design rather than a Cylone problem.

    Consult the Quartus software manual about the methods to release an asynchronous reset synchronously. Generally, applying an asynchronous reset while the clock is yet running often results in unxpected behaviour due to timing violations on reset realease.
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Thanks for replying~~~ :)

    But in my design I did pass the reset signal through a series of Dffs, and then "or"ed the original "reset" and synchronized "reset" to make a safe reset signal for internal use. As far as I know, this approach can reliably remove metastability and unexpectancy on reset release, and this is how I did reset for ASIC designs. I think it should also work for FPGA designs, am I right?

    Also, note that if I use "integer cnt" instead of "reg [3:0] cnt", the counter can be correctly reset to expected value upon reset, on the same PCB board using the same reset. Can anyone tell me what makes the difference between "reg"s and "integer"s?

    btw, which chapter in Quartus software manual talked about the Altera methods to release an asynchronous reset synchronously? I don't remember reading about this in the manual -_-

    Thanks & Danke!