>> I've been to the Xilinx website and looked at the various "development 
>> boards" they offer, and most of them seem to be around $2,000. Obviously 
>> I don't have that kind of money. I'll have to hunt around further to see 
>> if they offer anything at more sane prices.
> 
> Try Sparkfun:
> 
>   http://www.sparkfun.com/commerce/product_info.php?products_id=8458
>   http://www.sparkfun.com/commerce/product_info.php?products_id=8460
>   http://www.sparkfun.com/commerce/product_info.php?products_id=8595

That sounds more like it...

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> 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.

Atmel makes CPLDs and FPGAs, too.

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>> 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.

An EPROM usually works by having a little lense over the die surface, 
through which you fire UV radiation to cause chemical changes in the 
chip material which either 'connects' or 'disconnects' circuit pathways, 
thus forming a ROM.

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.

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

> Atmel makes CPLDs and FPGAs, too.

Right, OK.

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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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Aydan wrote:

>> 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

Interesting. I was under the impression that you use UV to program it 
too - much the same way that you use a laser to burn a CD. (Obviously 
you don't actually "burn" anything; you induce a chemical change in the 
ink.)

>> Of course, flash RAM uses chemical changes to permanently store data
>> too;
> 
> Wrong. Works the same as in eeprom with electricity and trapped electrons

Again, I was under the impression that you use a large current to 
chemically change the components such that they now respond to 
electricity differently, and that's how you store information.

>> 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.

Mmm, OK.

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Invisible <voi### [at] devnull> wrote:
> Again, I was under the impression that you use a large current to
> chemically change the components such that they now respond to
> electricity differently, and that's how you store information.

PROMs work this way. Either by fuse and current or antifuse and voltage.
The change is more physical than chemical though.

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Invisible 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.

nope. FPGA == Field Programmable Gate Array, with the emphasis on 'Field'.
i.e. it has to be re-configured each time it powers on. typically used in
applications where the FPGA (for obvious reasons) is not needed to get the
system booted. (Actually you can attach serial EEPROM's to them to auto-
configure them at startup if you wish). Some newer FPGA's incorporate this
device into the FPGA itself. Configuration is done serially (basically just
a bitstream).

Here's a write-up on them anyhow:

  http://en.wikipedia.org/wiki/Field-programmable_gate_array

-- Chris

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Chris Cason wrote:

> nope. FPGA == Field Programmable Gate Array, with the emphasis on 'Field'.
> i.e. it has to be re-configured each time it powers on.

Field-programmable just means it can be reprogrammed "in the field". 
Doesn't say how often. ;-) But yeah, OK...

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http://blog.orphi.me.uk/
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Invisible wrote:
> So I know there's a fairly diverse set of people in here so... Anybody 
> have any experience with using FPGAs? It's something I've often thought 
> of playing with, but I have no idea (1) how much it costs, and (2) how 
> difficult it is to make something that works.

NB at it appears you are interested in getting into hardware, you might be
interested in looking at the Hammer board:

  http://www.tincantools.com/

Particularly their hammer kit, which comes with a very nice prototyping
board. I have one of these and it's easily the best of the various embedded
development kits I've had over the years. My previous platform for personal
projects (up until a few months ago) was the gumstix (gumstix.com) but
while it's OK for plug-and-play, I found doing custom hardware work with it
to be a bit of a pain (particularly due to its small connectors and overall
mechanical setup).

The nice thing about the hammer (apart from the dev board) is the fact it's
got a standard 40-pin DIP form-factor, meaning it's very easy to wire into
custom projects. Of course you lose some flexibility in that you have very
few I/O pins to play with, but currently it's got all I need.

-- Chris

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Chris Cason wrote:

> NB at it appears you are interested in getting into hardware, you might be
> interested in looking at the Hammer board:
> 
>   http://www.tincantools.com/
> 
> Particularly their hammer kit, which comes with a very nice prototyping
> board. I have one of these and it's easily the best of the various embedded
> development kits I've had over the years. My previous platform for personal
> projects (up until a few months ago) was the gumstix (gumstix.com) but
> while it's OK for plug-and-play, I found doing custom hardware work with it
> to be a bit of a pain (particularly due to its small connectors and overall
> mechanical setup).
> 
> The nice thing about the hammer (apart from the dev board) is the fact it's
> got a standard 40-pin DIP form-factor, meaning it's very easy to wire into
> custom projects. Of course you lose some flexibility in that you have very
> few I/O pins to play with, but currently it's got all I need.

Mmm, interesting...

I seem to have misplaced it, but *somewhere* I have a box of 7400s and 
some breadboard. If you chop up lots of wire and hot A LOT of patience, 
you can wire up arbitrary logic devices with it. Latches, counters, 
mutiplexers, etc. I always wanted to sit down and wire up an actual 
processor. I mean, it's one thing thinking you know roughly how to do 
it. But the proof is in DOING it. ;-)

I just thought an FPGA sounds easier than plugging in millions of wires 
and then trying to figure out why nothing is working. :-}

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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