Using a Karnaugh map I need to

Oct 23, 2005 29 Replies

I like them because they're easy to understand, friendly to comment, usually are bug-free, and keep fanout down, which helps speed. It's easy to duplicate state flops off-to-the-side (two-hot design?) to reduce fanout with no speed penalty. I should note that I do most logic design as schematics and pretty much expect the FPGA software to plop down a flipflop where I tell it to.

I don't mind trusting a compiler to reduce combinatorial logic for me, but I still design the logic with the FPGA cell architecture in the back of my head, so I pretty much know what's going to happen and how deep the logic will have to be.

John

Curious, why do you like one-hots? I agree that they're generally preferable with FPGA state machines but explicitly coding them seems to go against the grain. I always use enumerated types for state variables and either let the software decide on the encoding or override it (if software chooses poorly) with an attribute.

Keith

Again. one-hots are generally better in FPGAs, but "binary" or "gray" encodings are sometimes better. Since I use VHDL for control logic (I would prefer to use schematics for data-flow, but haven't mixed them) the encoding isn't really all that important to

*me*. VHDL pretty well documents the state transitions.

State transition logic is no more than combinatorial logic. ;-)

Sure, I do the same, though in VHDL. Since synthesizers use templates, I know pretty much what logic is going to come out of what VHDL coding style. Of course there are FPGA-specific features (e.g. fast-carry chains) that may not drop out of behavioral style code and structural coding is needed for maximum speed. This sort of thing also limits portability, which is important to some.

Keith

If the power switch #1 is off do you have another source of power to run the logic?

DarkPath wrote: [snip garbage]

Try this logic:

ENGINEERING= HARD_WORK AND APTITUDE

DARKPATH= NOT HARD_WORKER AND NOT APTITUDE

ACTION=DARKPATH_GO_DO_SOMETHING_ELSE

Is that you, Yoda?

-- Paul Hovnanian mailto: snipped-for-privacy@Hovnanian.com

------------------------------------------------------------------ "Si hoc legere scis nimium eruditionis habes." (If you can read this, you're overeducated.)

I can still remember some of that stuff, more than 50 years after having 4 years of Latin in high/junior-high school ;-)

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

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| 1962 | I love to cook with wine. Sometimes I even put it in the food.

Well a design with 10% fewer packages, 1% lower manufacturing cost, and twice the sales is a better deal for the involved parties. Application engineers did a lot of that also.

JosephKK

Just the same 5 inputs and 4 outputs is subgrade even for the venerable

22V10. Interacting state machines can also make tractable things that are otherwise not so (like PCI bus).
JosephKK

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