Invisible <voi### [at] devnull> wrote:
> >> OK, that's news. I was under the impression that an FPGA works something
> >> like an EPROM - you use UV to erase it and then program in all the
> >> circuit connections, and thereafter it just works.
> >
> > Some are OTP (one time programmable) but most are flash based today.
>
> A PROM is OTP; an EPROM (Erasable PROM) can be reused.

True
>
> An EPROM usually works by having a little lense over the die surface,
> through which you fire UV radiation
Correct

> to cause chemical changes in the
> chip material which either 'connects' or 'disconnects' circuit pathways,
> thus forming a ROM.

Partly right. You erase with UV-radiation and program with a higher than usual
voltage
The programming works by trapping electrons inside an insulated gate of the
field effect transistors used to form the logic gates thus enabling the
connection. The erasing via UV gives the trapped electrons enough energy to
leave the gate and thus disabling the transistor

>
> I was under the impression that FPGAs work in the same way, except
> instead of opening and closing contacts between data lines and the power
> rails to make bit patterns, you actually connect and disconnect blocks
> of circuitry to make a custom circuit configuration.

THat's how it works. You have switch matrices which connect logic blocks and I/O
pins with each other and also configure the logic blocks.

>
> Of course, flash RAM uses chemical changes to permanently store data
> too;

Wrong. Works the same as in eeprom with electricity and trapped electrons

> you just don't need the lense and the UV radiation. But I didn't
> think you could use that technology to physically change connections...
>

you don't physically change connections but control switches in the connections.

> > Atmel makes CPLDs and FPGAs, too.
>
> Right, OK.
>
> --
> http://blog.orphi.me.uk/
> http://www.zazzle.com/MathematicalOrchid*

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