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'[PIC] dsPIC SPI speed'
2007\07\20@170540 by Andre Abelian

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Hi to all,

At work I am working on a project that uses floating point co processor
witch is dsPIC30F3012 and it uses internal clock. I am working
on this project over a month now and I am having terrible time to make it work.
floating point co processor lets call it FPU.
Since I do not see any external crystal it means it uses internal RC
maybe with PLL. My question is how fast SPI clock is possible to generate
using internal clock. At this moment fastest I was able to use to talk to
FPU was 24 us (microseconds). main schematic looks like this I am using
my own pic thru SPI is connected to FPU spi interface. As soon as I increase
the speed of SPI it quits working and one of our other engineer blames me
that it is my problem. I already know that dsPIC is using hardware SPI
as far as PLL I have no idea how it is setup in dsPIC.

any idea will appreciate.

Andre

2007\07\20@171800 by Xiaofan Chen

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On 7/20/07, Andre Abelian <spam_OUTaabelianTakeThisOuTspammason-electric.com> wrote:
> Hi to all,
>
> At work I am working on a project that uses floating point co processor
> witch is dsPIC30F3012 and it uses internal clock. I am working
> on this project over a month now and I am having terrible time to make it work.
> floating point co processor lets call it FPU.
> Since I do not see any external crystal it means it uses internal RC
> maybe with PLL. My question is how fast SPI clock is possible to generate
> using internal clock. At this moment fastest I was able to use to talk to
> FPU was 24 us (microseconds). main schematic looks like this I am using
> my own pic thru SPI is connected to FPU spi interface. As soon as I increase
> the speed of SPI it quits working and one of our other engineer blames me
> that it is my problem. I already know that dsPIC is using hardware SPI
> as far as PLL I have no idea how it is setup in dsPIC.
>

Try to use a crystal and see if it helps.

2007\07\20@190744 by Andre Abelian

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What I mean is the part I am using is dsPIC it is some one else's part
here is the link
http://www.micromegacorp.com/

my board uses 18F4550 to talk to that chip which happed to be dsPIC.

Andre



{Original Message removed}

2007\07\20@194753 by Dave Mumert

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Hi

Here is what the manual says about clock speed.  It defaults to 1.8432 MHz
so your clock speed may be too slow to support the SPI speed to are using.
You could switch to an external crystal or perhaps you have selected an
external crystal and it is not there forcing it to return to default.


Manual Quote follows:
Clock - select clock source
The Clock command allows you to change the clock source. The clock source is
stored in Flash memory as part of the device configuration bits. The clock
selection indicates the clock source to use at power-up. If the selected
clock source can't be validated at power-up, the uM-FPU V3.1 chip will
default to an internal clock of 1.8425 MHz. The available clock speeds and
clock sources are selected by entering one of the following values:

Value Clock Speed Clock Source
20 1.8425 MHz internal oscillator
E1 7.37 MHz internal oscillator
EA 14.74 MHz internal oscillator
E3 29.48 MHz internal oscillator
E5 10.0 MHz external 10.0 MHz crystal
E6 20.0 MHz external 10.0 MHz crystal
E7 29.4912 MHz external 7.3728 MHz crystal

Good Luck

Dave

>
> What I mean is the part I am using is dsPIC it is some one else's part
> here is the link
> http://www.micromegacorp.com/
>
> my board uses 18F4550 to talk to that chip which happed to be dsPIC.
>
> Andre
>

2007\07\20@205344 by Jinx

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> dsPIC is using hardware SPI as far as PLL I have no idea how
> it is setup in dsPIC

AFAIK, the FRC option (8MHz internal) doesn't work with PLL.
PLL can be applied only to the primary oscillator

So, maybe you can assume that the 3012 is running at 8MHz. You'd
think that would be the fastest simplest configuration. If so, then you
could work out what the highest SPI rate would be. Don't uM give
any information like that ? What speed do you get up to before the
SPI fails ?


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