At 15:44 21/08/99 -0700, you wrote:
>   Andy, again the problem is implementing the FIFO. The ISA interface and
>FIFO control is trivial. Since you already have the design in 2 FIFO's and a
>22V10, moving the FIFO to a CPLD would dramatically raise the cost and it
>would require a large device due to the number of internal registers needed.
>Lattice and others have devices with internal FIFO's but they are very
>expensive and large, typically over 200 pins in xQFP packages. When
>designing custom chips there is always a `battle' between internal resources
>and available I/O. In the above case, you would be using a large portion of
>the internal resources and a small fraction of the I/O but you will be
>paying for it...
>
>   Without knowing the details of the design, I would take a hard look at
>how large a FIFO you really need. For example 16 Bytes could easily fit in a
>smaller CPLD.
>
>   I'll admit I haven't thought this through but I was thinking of using
>external logic to control a dual-port SRAM. In this case, you are just
>implementing a dual FIFO with the advantage of using one chip for data
>storage. There is a suitable Lattice CPLD that comes in a 68-pin PLCC or
>100-pin TQFP (14mm x 14mm) package. This would cut board `real-estate' by
>more than half but it might increase the cost...
>
>   Believe me, I could use the work right now but unless board space is
>`mission critical' compared to cost, I think the existing design is more
>cost-effective depending on how much you are paying for the 7201s.
>
>   - Tom

I could not agree more. The problem with the high end FPGAs is size, it
seems that the manufactures in order to keep things as generic as possible
make the thing quite large with lotsa IO, CLBS and that sort of stuff.
Fortunatly they have seen the light and are now offering a bit more of
fixed type stuff in the FPGAs (See paper delivered to the Custom
intergrated circut conference in San Diego this year by the University of
London and Averio) This basicaly requests that some special functions be
placed into these etc.



Dennis



>
>At 10:43 AM 8/20/99 -0400, Andy Kunz wrote:
>>Board space is the problem.  We have two IDT 7201 FIFOs and a GAL22V10 on
>>it now, and it would sure be nice to get the whole mess into one small
>>package.  Also simplify the snot out of routing it.
>>
>>I don't care whose parts get used, so long as it works.  Lattice is a good
>>choice by me, since they have good local support from the vendor here.
>>
>>What would it take to convince you to write the logic (I have the 22V20
>>source I can send you).
>>
>>Andy
>
>
>------------------------------------------------------------------------
>Tom Handley
>New Age Communications
>Since '75 before "New Age" and no one around here is waiting for UFOs ;-)
>
>