ARM controller with integrated DAC

On Aug 17, 9:37=A0am, "RockyG" <RobertGush@n_o_s_p_a_m.gmail.com> wrote:
> >Comes the analog part: If the software can provide data every 100 ns
> >which hardware will turn it into analog values?
>
> You are only looking for 5 bit accuracy, about 3%.
> 5 resistors on a port could give this to you.
>
> BIT0 81k accurate enough
> BIT1 39k accurate enough
> BIT2 20k available 1%
> BIT3 10k available 1%
> BIT4 5k0 2* 10k in parallel
>
> You may need lower values to get the desired frequency response, but ther=
e
> is a tradeoff with the port drive capability. =A0 =A0 =A0

Feed them into an op-amp.  You can use much lower values.

> The idea is to produce short bursts of a duration of appr. 3 - 5 �s
> every 100 �s using _pre-defined_ values (this is for testing external
> equipment). So I started to look at it from the software side:
> - Can we store the data we need in memory? No question, 5 �s will need
> only 50 values (if providing data @ 100 ns intervalls).
> - Can we provide the data fast enough (a new value every 100 ns)? This
> shouldn't be a problem either: DMA is a possibility or we might even
> just loop inside an ISR for those 5 �s writng out new values when
> needed (the processor won't be doing much else during that time).


Michael,

If it was me I'd use a small FPGA to drive the data, pre-loading it from the
uC.

How many bursts do you need during a test?


Nial. 

On Wed, 18 Aug 2010 10:52:39 +0100, "Nial Stewart"
<nial*REMOVE_THIS*@nialstewartdevelopments.co.uk> wrote:

>> The idea is to produce short bursts of a duration of appr. 3 - 5 &#4294967295;s
>> every 100 &#4294967295;s using _pre-defined_ values (this is for testing external
>> equipment). So I started to look at it from the software side:
>> - Can we store the data we need in memory? No question, 5 &#4294967295;s will need
>> only 50 values (if providing data @ 100 ns intervalls).
>> - Can we provide the data fast enough (a new value every 100 ns)? This
>> shouldn't be a problem either: DMA is a possibility or we might even
>> just loop inside an ISR for those 5 &#4294967295;s writng out new values when
>> needed (the processor won't be doing much else during that time).

Hi Nial,
>If it was me I'd use a small FPGA to drive the data, pre-loading it from the
>uC.
we don't know much about FPGAs around here but get along with MVUs
rather well.

>How many bursts do you need during a test?
During one test the same burst (consisting of ~50 values) is repeated
over and over every 100 &#4294967295;s as often as desired, the actual number
shouldn't matter.

Thanks for your feedback
M'

On 16 Aug, 14:51, Michael Keith <mjke...@gmx.de> wrote:
> Hi David,
> thanks for your comments.>Why do you want an integrated DAC?
>
> well, as a first idea it seemed like a nice feature.
> Meanwhile I found that the (rather new) LPC1765/66/68 come with a DAC.
>
> Don't laugh - I am a software guy, not an EE and was just tasked to
> evaluate a new idea of my boss. Turns out the DAC in the ARM is too
> slow: It has a maximal conversion rate of 1 =B5s.> What
> >are your requirements for the DAC - channels, resolution, speed, etc.?
>
> Bad news: We will produce data at the rate of 200 ns (and maybe even
> down to 100 ns).
> (Hopefully) good news: We only need a very low resolution, 5 bit will
> be sufficient (and we need only one channel).
>
> My knowledge of analog conversion is limited to
> - DACs exist and
> - (from very long ago) a faint memory of R-2R-networks.
> Any link to information on how to perform D/A conversion at the rate
> mentioned above would be welcome. I could hand it over to an EE
> colleage to understand the technical details.
>
> Thanks
> M'

If you need a really fast DAC, simply interface one to an XMOS chip:

http://www.xmos.com

Development will be much easier than if you used an FPGA. You could
buy one of these Sparkfun boards and XTAG2 for $100 and add a DAC to
it:

http://www.sparkfun.com/commerce/product_info.php?products_id=3D9428

Hi Leon,
>If you need a really fast DAC, simply interface one to an XMOS chip:
>
>http://www.xmos.com
>
>Development will be much easier than if you used an FPGA. You could
we didn't consider an FPGA. Our intention was to use an ARM (or a
similar processor).
Reason 1: familiarity
Reason 2: price tag $1 - $2
While we could waive reason 1 it would only make sense if it offers a
significant advantage for reason 2: arrive at a price tag below $2 at
1k units. I would be surprised if there are any chips (FPGAs or XMOS
or ???) which meet this requirement, but then this domain is a foreign
one for me.

Anybody knows if there are chips in this price range? Our requirements
wrt gate count are probably rather low, given what is possible in
modern hardware. (I know that 'rather low' is vague, but as I said we
originally didn't consider it and it is foreign territory.)

Thanks for your feedback
M'

On 18 Aug, 16:18, Michael Keith <mjke...@gmx.de> wrote:
> Hi Leon,>If you need a really fast DAC, simply interface one to an XMOS chip:
>
> >http://www.xmos.com
>
> >Development will be much easier than if you used an FPGA. You could
>
> we didn't consider an FPGA. Our intention was to use an ARM (or a
> similar processor).
> Reason 1: familiarity
> Reason 2: price tag $1 - $2
> While we could waive reason 1 it would only make sense if it offers a
> significant advantage for reason 2: arrive at a price tag below $2 at
> 1k units. I would be surprised if there are any chips (FPGAs or XMOS
> or ???) which meet this requirement, but then this domain is a foreign
> one for me.
>
> Anybody knows if there are chips in this price range? Our requirements
> wrt gate count are probably rather low, given what is possible in
> modern hardware. (I know that 'rather low' is vague, but as I said we
> originally didn't consider it and it is foreign territory.)
>
> Thanks for your feedback
> M'

The cheapest XMOS chip is $4.92 for 5000+. You might not be able to
find anything that will do what you want for the price you quoted.

On Aug 18, 8:18=A0am, Michael Keith <mjke...@gmx.de> wrote:
> Hi Leon,>If you need a really fast DAC, simply interface one to an XMOS c=
hip:
>
> >http://www.xmos.com
>
> >Development will be much easier than if you used an FPGA. You could
>
> we didn't consider an FPGA. Our intention was to use an ARM (or a
> similar processor).
> Reason 1: familiarity
> Reason 2: price tag $1 - $2
> While we could waive reason 1 it would only make sense if it offers a
> significant advantage for reason 2: arrive at a price tag below $2 at
> 1k units. I would be surprised if there are any chips (FPGAs or XMOS
> or ???) which meet this requirement, but then this domain is a foreign
> one for me.
>
> Anybody knows if there are chips in this price range? Our requirements
> wrt gate count are probably rather low, given what is possible in
> modern hardware. (I know that 'rather low' is vague, but as I said we
> originally didn't consider it and it is foreign territory.)

You can get a small CPLD (need milk^H^H^Hemory) for $1, couple with an
external sram (free).  You can pull sram chip out of any old
motherboard (or module).  Add an op-amp for 50 cents and you can build
the whole thing below $2.

> On Aug 18, 8:18 am, Michael Keith<mjke...@gmx.de>  wrote:
>>
>> we didn't consider an FPGA. Our intention was to use an ARM (or a
>> similar processor).
>> Reason 1: familiarity
>> Reason 2: price tag $1 - $2


The OPs goals are not possible.

As a professed software guy, he does not understand the hardware 
requirements to do the task.

Or he has wishful thinking as most software people do.

My $.02

hamilton

On Aug 18, 9:43=A0am, hamilton <hamil...@nothere.com> wrote:
> > On Aug 18, 8:18 am, Michael Keith<mjke...@gmx.de> =A0wrote:
>
> >> we didn't consider an FPGA. Our intention was to use an ARM (or a
> >> similar processor).
> >> Reason 1: familiarity
> >> Reason 2: price tag $1 - $2
>
> The OPs goals are not possible.

Part only for CPLD is reasonable, FPGA is not.

>> Hi Leon,>If you need a really fast DAC, simply interface one to an XMOS chip:
>>
>> >http://www.xmos.com
>>
>> >Development will be much easier than if you used an FPGA. You could
>>
>> we didn't consider an FPGA. Our intention was to use an ARM (or a
>> similar processor).
>> Reason 1: familiarity
>> Reason 2: price tag $1 - $2
>> While we could waive reason 1 it would only make sense if it offers a
>> significant advantage for reason 2: arrive at a price tag below $2 at
>> 1k units. I would be surprised if there are any chips (FPGAs or XMOS
>> or ???) which meet this requirement, but then this domain is a foreign
>> one for me.
>>
>> Anybody knows if there are chips in this price range? Our requirements
>> wrt gate count are probably rather low, given what is possible in
>> modern hardware. (I know that 'rather low' is vague, but as I said we
>> originally didn't consider it and it is foreign territory.)
>>
>> Thanks for your feedback
>> M'
>
>The cheapest XMOS chip is $4.92 for 5000+. You might not be able to
>find anything that will do what you want for the price you quoted.
Well, looks like there is no reason to not use an ARM.
Thanks
M'