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Old 11-09-2007, 03:54 AM
Gabor
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Default Re: FIFO interface design

On Nov 8, 8:25 pm, Readon <[email protected]> wrote:
> On Nov 9, 8:07 am, Dave Pollum <[email protected]> wrote:
>
>
>
> > On Nov 8, 8:15 am, Readon <[email protected]> wrote:

>
> > > i want to read & write data to/from a fifo placed in fpga. MCU's
> > > external bus is connected to the chip. I am using the sync-fifo ip of
> > > Altera CycloneII. The data bus and control signal are connected to
> > > fifo directly. it's unfortune that when i read once from bus, data
> > > would be read twice from fifo because there are two clock rising edges
> > > during read signal(low active) is resetted. I think it will read more
> > > datas from fifo if the read signal is resetted long enough.
> > > Is there any good design for fifo interface connecting on the
> > > exteranl bus?

>
> > Using a Synchronous FIFO implies that the read clock and the write
> > clock are in the same clock domain. Is your MCU supplying the FIFO's
> > clock or is the FPGA supplying the MCU's clock? If the clock sources
> > are different, then you either need an Asynchronous FIFO, or you need
> > to run the MCU and FPGA from the same clock.
> > HTH
> > -Dave Pollum

>
> It is in different clock, i tried altera's asynchronous FIFO which
> need two extra clock for reading.
> is there any better solution?



If your MCU is running much slower than the FPGA, you can use the
FPGA's internal clock to run the synchronous FIFO, and a little
state logic to generate the necessary (single cycle) pulses for
read and write from the MCU interface signals.

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