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Discussion Groups | LPC2000 | Re: LPC2458 USB/Ethernet w/IRC clock?
Discussion group dedicated to the Philips LPC2000 family of ARM MCUs
LPC2458 USB/Ethernet w/IRC clock? - "David L. Miller" - Jun 17 13:34:53 2008
I have an application where I cannot use a crystal oscillator, but
still need a high speed serial interface. Does anyone know if the USB
or Ethernet can be used reliably with only the IRC? I don't see
anything definitive in the datasheet...
Thanks!
--DLM
------------------------------------
(You need to be a member of lpc2000 -- send a blank email to lpc2000-subscribe@yahoogroups.com )
still need a high speed serial interface. Does anyone know if the USB
or Ethernet can be used reliably with only the IRC? I don't see
anything definitive in the datasheet...
Thanks!
--DLM
------------------------------------
(You need to be a member of lpc2000 -- send a blank email to lpc2000-subscribe@yahoogroups.com )
Re: LPC2458 USB/Ethernet w/IRC clock? - lpc2100_fan - Jun 17 15:03:07 2008
--- In l...@yahoogroups.com, "David L. Miller" wrote:
>
> I have an application where I cannot use a crystal oscillator, but
> still need a high speed serial interface. Does anyone know if the USB
> or Ethernet can be used reliably with only the IRC? I don't see
> anything definitive in the datasheet...
>
> Thanks!
>
> --DLM
>
Hi Dave,
the specification is the accuracy of the IRC which is typically 1% but
worst case IIRC better than 2%. While the Ethernet is a synchronous
interface that gets an external clock and can absolutely be used with
the IRC, USB has a spec afaik from required clock accuracy of less
than 0.1% deviation.
So, IMHO Ethernet no problem, USB not really. It might still work but
your system is out of specification
Bob
------------------------------------
(You need to be a member of lpc2000 -- send a blank email to lpc2000-subscribe@yahoogroups.com )
>
> I have an application where I cannot use a crystal oscillator, but
> still need a high speed serial interface. Does anyone know if the USB
> or Ethernet can be used reliably with only the IRC? I don't see
> anything definitive in the datasheet...
>
> Thanks!
>
> --DLM
>
Hi Dave,
the specification is the accuracy of the IRC which is typically 1% but
worst case IIRC better than 2%. While the Ethernet is a synchronous
interface that gets an external clock and can absolutely be used with
the IRC, USB has a spec afaik from required clock accuracy of less
than 0.1% deviation.
So, IMHO Ethernet no problem, USB not really. It might still work but
your system is out of specification
Bob
------------------------------------
(You need to be a member of lpc2000 -- send a blank email to lpc2000-subscribe@yahoogroups.com )
Re: LPC2458 USB/Ethernet w/IRC clock? - "David L. Miller" - Jun 17 18:29:18 2008
--- In l...@yahoogroups.com, "lpc2100_fan"
wrote:
>
> --- In l...@yahoogroups.com, "David L. Miller"
wrote:
> >
> > I have an application where I cannot use a crystal oscillator,
but
> > still need a high speed serial interface. Does anyone know if
the USB
> > or Ethernet can be used reliably with only the IRC? I don't see
> > anything definitive in the datasheet...
> >
> Hi Dave,
>
> the specification is the accuracy of the IRC which is typically 1%
but
> worst case IIRC better than 2%. While the Ethernet is a synchronous
> interface that gets an external clock and can absolutely be used
with
> the IRC, USB has a spec afaik from required clock accuracy of less
> than 0.1% deviation.
>
> So, IMHO Ethernet no problem, USB not really. It might still work
but
> your system is out of specification
>
> Bob
>
OK, USB is out. I could do Ethernet, but that requires an external
PHY. How about the SSP? According to the datasheet the maximum bit
rate for SSP master is 1/2 of the input clock rate. When using the
IRC, would that mean 4MHz/2 = 2Mbps, or does it mean CCLK?
Thanks!
--DLM
------------------------------------
(You need to be a member of lpc2000 -- send a blank email to lpc2000-subscribe@yahoogroups.com )
wrote:
>
> --- In l...@yahoogroups.com, "David L. Miller"
wrote:
> >
> > I have an application where I cannot use a crystal oscillator,
but
> > still need a high speed serial interface. Does anyone know if
the USB
> > or Ethernet can be used reliably with only the IRC? I don't see
> > anything definitive in the datasheet...
> >
> Hi Dave,
>
> the specification is the accuracy of the IRC which is typically 1%
but
> worst case IIRC better than 2%. While the Ethernet is a synchronous
> interface that gets an external clock and can absolutely be used
with
> the IRC, USB has a spec afaik from required clock accuracy of less
> than 0.1% deviation.
>
> So, IMHO Ethernet no problem, USB not really. It might still work
but
> your system is out of specification
>
> Bob
>
OK, USB is out. I could do Ethernet, but that requires an external
PHY. How about the SSP? According to the datasheet the maximum bit
rate for SSP master is 1/2 of the input clock rate. When using the
IRC, would that mean 4MHz/2 = 2Mbps, or does it mean CCLK?
Thanks!
--DLM
------------------------------------
(You need to be a member of lpc2000 -- send a blank email to lpc2000-subscribe@yahoogroups.com )