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The right crystal for 70Mhz LPC2103

Started by Gus December 26, 2005
What would be the closest crystal to 70 Mhz while keeping the
standard UART baud rates?

It would be nice if it would work with x6 pll multiplier so we an
stop the pll to go in lower power mode

Gus


An Engineer's Guide to the LPC2100 Series

Gus,

The PC210x has the fractional division register so I think you'll find
there are a number of crystals that are candidates.

-- Paul.

> -----Original Message-----
> From: Gus [mailto:gus_is_working@gus_...]
> Sent: 26 December 2005 18:30
> To: lpc2000@lpc2...
> Subject: [lpc2000] The right crystal for 70Mhz LPC2103 > What would be the closest crystal to 70 Mhz while keeping the
> standard UART baud rates?
>
> It would be nice if it would work with x6 pll multiplier so we an
> stop the pll to go in lower power mode
>
> Gus >
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Gus,

the LPC2103 has a fractional BR-Generator. So you could e.g. take 10
MHz and multiply it with 7 and still get 115200 Baud fairly excactly.
If I remember it right, the actual bausrate difference is less than 1%

Bob

--- In lpc2000@lpc2..., "Gus" <gus_is_working@y...> wrote:
>
> What would be the closest crystal to 70 Mhz while keeping the
> standard UART baud rates?
>
> It would be nice if it would work with x6 pll multiplier so we an
> stop the pll to go in lower power mode
>
> Gus
>




---- Original Message ----
From: "Gus" <gus_is_working@gus_...>
To: <lpc2000@lpc2...>
Sent: Monday, December 26, 2005 7:30 PM
Subject: [lpc2000] The right crystal for 70Mhz LPC2103

> What would be the closest crystal to 70 Mhz while keeping the
> standard UART baud rates?
>
> It would be nice if it would work with x6 pll multiplier so we an
> stop the pll to go in lower power mode

The LPC2101/02/03 have the fractional baudrate generator, so you can get
almost any baudrates with any crystal. 10 MHz lets you hit 70 MHz exactly,
and pclk = 70 MHz also gets almost exact baud rates without the fractional
divider.

10 MHz only lets you do ISP with 38400 bps, but it is less important with
the limited amount of flash to program.

Karl Olsen


> What would be the closest crystal to 70 Mhz while keeping the
> standard UART baud rates?
>
> It would be nice if it would work with x6 pll multiplier so we an
> stop the pll to go in lowe

Hi Gus,

I posted this tool a while back, it's used to determine the optimal
fractional divider values for any given PCLK and baud rate. It applies to
all LPC devices with fractional divider enabled UARTs, which are currently
the LPC214x and the LPC2101/LPC2101/LPC2103.

http://groups.yahoo.com/group/lpc2000/files/Tools/lpc2fdcalc.exe Joel