1. This forum section is a read-only archive which contains old newsgroup posts. If you wish to post a query, please do so in one of our main forum sections (here). This way you will get a faster, better response from the members on Motherboard Point.

AT91SAM7S XTAL Selection

Discussion in 'Embedded' started by Ian Mcbride, Oct 3, 2005.

  1. Ian Mcbride

    Ian Mcbride Guest

    Is there a "standard" crystal value for AT91SAM7S designs?

    It seems that the boot program would expect something specific for proper
    configuration of the PLL, serial, and USB devices. However, I can't find
    any guidance in the documentation.
    Ian Mcbride, Oct 3, 2005
    #1
    1. Advertising

  2. "Ian Mcbride" <> skrev i meddelandet
    news:Dv90f.7842$...
    > Is there a "standard" crystal value for AT91SAM7S designs?
    >
    > It seems that the boot program would expect something specific for proper
    > configuration of the PLL, serial, and USB devices. However, I can't find
    > any guidance in the documentation.
    >
    >


    If you use an 18.432 Mhz crystal, then the USB can be used to flash the part
    at production.
    If you use anything else, then the USB will not work, but the UART will.


    --
    Best Regards,
    Ulf Samuelsson
    This is intended to be my personal opinion which may,
    or may bot be shared by my employer Atmel Nordic AB
    Ulf Samuelsson, Oct 3, 2005
    #2
    1. Advertising

  3. Ian Mcbride

    Ian Mcbride Guest

    "Ulf Samuelsson" <> wrote in message
    news:ksg0f.40152$...
    >
    > If you use an 18.432 Mhz crystal, then the USB can be used to flash the

    part
    > at production.
    > If you use anything else, then the USB will not work, but the UART will.


    Thanks, Ulf.

    The 18.432/48 ratio seems a bit wide for this PLL -- divide by 48, multiply
    by 125? This works OK with this part?
    Ian Mcbride, Oct 4, 2005
    #3
  4. >> If you use an 18.432 Mhz crystal, then the USB can be used to flash the
    > part
    >> at production.
    >> If you use anything else, then the USB will not work, but the UART will.

    >
    > Thanks, Ulf.
    >
    > The 18.432/48 ratio seems a bit wide for this PLL -- divide by 48,
    > multiply
    > by 125? This works OK with this part?
    >



    Download one of the USB examples...

    --
    Best Regards,
    Ulf Samuelsson
    This is intended to be my personal opinion which may,
    or may bot be shared by my employer Atmel Nordic AB
    Ulf Samuelsson, Oct 4, 2005
    #4
  5. Ian Mcbride

    Guest

    Ulf Samuelsson wrote:
    > "Ian Mcbride" <> skrev i meddelandet
    > news:Dv90f.7842$...
    > > Is there a "standard" crystal value for AT91SAM7S designs?
    > >
    > > It seems that the boot program would expect something specific for proper
    > > configuration of the PLL, serial, and USB devices. However, I can't find
    > > any guidance in the documentation.
    > >
    > >

    >
    > If you use an 18.432 Mhz crystal, then the USB can be used to flash the part
    > at production.
    > If you use anything else, then the USB will not work, but the UART will.


    If I use a 18.432 MHz crystal, then what values do I use for
    the caps and resistors connected to PLLRC?

    The datasheet contains very little information, but hints that
    there is a "tool" available to calculate the values. I searched
    Atmel's website, and all I could find was an Excel spreadsheet
    application. I downloaded it, and selected the part I am using,
    AT91SAM7256. The first inputs it asked for was the "Input
    Divider Ratio" and the "Loop Divider Ratio" with no explaination
    for what these numbers mean, or what criteria I should use to
    select them. Furthermore, it appears to be impossible to use
    the spreadsheet to select any values that result in an output
    frequency lower than 88MHz. Yet, according to the datasheet,
    the max frequency for the chip is 55MHz.

    The next number it asks for is the "PLL Frequency Bandwidth",
    with no explaination of what that means. The phrase "PLL
    Frequency Bandwidth" occurs nowhere in the 519 page datasheet.
    If I Google for "PLL Frequency Bandwidth" I get only one hit,
    for a non-relevant webpage on a server in Argentina.

    Sorry if I sound a little frustrated.

    -bob
    , Oct 5, 2005
    #5
  6. Ian Mcbride

    Guest

    Ulf Samuelsson wrote:
    > "Ian Mcbride" <> skrev i meddelandet
    > news:Dv90f.7842$...
    > > Is there a "standard" crystal value for AT91SAM7S designs?
    > >
    > > It seems that the boot program would expect something specific for proper
    > > configuration of the PLL, serial, and USB devices. However, I can't find
    > > any guidance in the documentation.
    > >
    > >

    >
    > If you use an 18.432 Mhz crystal, then the USB can be used to flash the part
    > at production.
    > If you use anything else, then the USB will not work, but the UART will.


    Why not use a 20Mhz xtal instead of a 18.432Mhz one?
    18.432Mhz divided by 5 and multiplied by 26 gives 95.846MHz, whereas
    20MHz divided by 5 multiplied by 24 gives exactly 96MHz, a better value
    for USB

    Is it just because 18.432xtals are cheaper than 20Mhz ones?

    ted
    , Oct 5, 2005
    #6
  7. Ian Mcbride

    Ian Mcbride Guest

    > Why not use a 20Mhz xtal instead of a 18.432Mhz one?
    > 18.432Mhz divided by 5 and multiplied by 26 gives 95.846MHz, whereas
    > 20MHz divided by 5 multiplied by 24 gives exactly 96MHz, a better value
    > for USB


    18.432MHz divided by 48, multiplied by 125 gives 48MHz.

    However, this would drive 384 KHz into the PLL, which is lower than the 1MHz
    specified minimum in the datasheet.

    BUT, the minimum output of the PLL is 80MHz and the data sheet talks about
    the PLL generating a 48MHz clock in quite a few places.. so I'm wondering if
    the PLL is a little wider than is specified.
    Ian Mcbride, Oct 6, 2005
    #7
  8. <> skrev i meddelandet
    news:...
    > Ulf Samuelsson wrote:
    >> "Ian Mcbride" <> skrev i meddelandet
    >> news:Dv90f.7842$...
    >> > Is there a "standard" crystal value for AT91SAM7S designs?
    >> >
    >> > It seems that the boot program would expect something specific for
    >> > proper
    >> > configuration of the PLL, serial, and USB devices. However, I can't
    >> > find
    >> > any guidance in the documentation.
    >> >
    >> >

    >>
    >> If you use an 18.432 Mhz crystal, then the USB can be used to flash the
    >> part
    >> at production.
    >> If you use anything else, then the USB will not work, but the UART will.

    >
    > If I use a 18.432 MHz crystal, then what values do I use for
    > the caps and resistors connected to PLLRC?
    >
    > The datasheet contains very little information, but hints that
    > there is a "tool" available to calculate the values. I searched
    > Atmel's website, and all I could find was an Excel spreadsheet
    > application. I downloaded it, and selected the part I am using,
    > AT91SAM7256. The first inputs it asked for was the "Input
    > Divider Ratio" and the "Loop Divider Ratio" with no explaination
    > for what these numbers mean, or what criteria I should use to
    > select them. Furthermore, it appears to be impossible to use
    > the spreadsheet to select any values that result in an output
    > frequency lower than 88MHz. Yet, according to the datasheet,
    > the max frequency for the chip is 55MHz.
    >
    > The next number it asks for is the "PLL Frequency Bandwidth",
    > with no explaination of what that means. The phrase "PLL
    > Frequency Bandwidth" occurs nowhere in the 519 page datasheet.
    > If I Google for "PLL Frequency Bandwidth" I get only one hit,
    > for a non-relevant webpage on a server in Argentina.


    Download the schematics from the atmel web page.
    Cut
    Paste
    Done ;-)



    --
    Best Regards,
    Ulf Samuelsson
    This is intended to be my personal opinion which may,
    or may bot be shared by my employer Atmel Nordic AB
    >
    > Sorry if I sound a little frustrated.
    >
    > -bob
    >
    Ulf Samuelsson, Oct 6, 2005
    #8
  9. <> skrev i meddelandet
    news:...
    >
    > Ulf Samuelsson wrote:
    >> "Ian Mcbride" <> skrev i meddelandet
    >> news:Dv90f.7842$...
    >> > Is there a "standard" crystal value for AT91SAM7S designs?
    >> >
    >> > It seems that the boot program would expect something specific for
    >> > proper
    >> > configuration of the PLL, serial, and USB devices. However, I can't
    >> > find
    >> > any guidance in the documentation.
    >> >
    >> >

    >>
    >> If you use an 18.432 Mhz crystal, then the USB can be used to flash the
    >> part
    >> at production.
    >> If you use anything else, then the USB will not work, but the UART will.

    >
    > Why not use a 20Mhz xtal instead of a 18.432Mhz one?
    > 18.432Mhz divided by 5 and multiplied by 26 gives 95.846MHz, whereas
    > 20MHz divided by 5 multiplied by 24 gives exactly 96MHz, a better value
    > for USB
    >
    > Is it just because 18.432xtals are cheaper than 20Mhz ones?
    >



    No, because the BootROM assumes 18,432 Mhz.
    The SAM-BA USB flashing wont work without it, and you have to use the UART.
    --
    Best Regards,
    Ulf Samuelsson
    This is intended to be my personal opinion which may,
    or may bot be shared by my employer Atmel Nordic AB
    Ulf Samuelsson, Oct 6, 2005
    #9
  10. Ian Mcbride

    Guest

    Ulf Samuelsson wrote:
    > <> skrev i meddelandet
    > > If I use a 18.432 MHz crystal, then what values do I use for
    > > the caps and resistors connected to PLLRC?

    >
    > Download the schematics from the atmel web page.


    Hi Ulf,
    Can you please provide a URL? I went to www.atmel.com
    and searched for "schematic AT91SAM7S", and some other
    combinations, but didn't find anything useful.

    Thanks,

    -bob
    , Oct 6, 2005
    #10
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. Guest
    Replies:
    26
    Views:
    839
    Larry Brasfield
    Feb 27, 2005
  2. orc

    AT91SAM7S oscillator?

    orc, Apr 13, 2005, in forum: Embedded
    Replies:
    2
    Views:
    442
  3. Bob

    Smallest Xtal

    Bob, Dec 16, 2005, in forum: Embedded
    Replies:
    14
    Views:
    499
    Jim Stewart
    Dec 20, 2005
  4. StanV
    Replies:
    2
    Views:
    917
    An Schwob in the USA
    Feb 1, 2006
  5. Xtal choice for Pic16f88

    , Mar 4, 2008, in forum: Embedded
    Replies:
    1
    Views:
    346
    Tim Wescott
    Mar 4, 2008
Loading...

Share This Page