LPC17xx ClkOut function as system clock

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Wed, 2012-08-08 00:06
tech19
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Joined: 2012-08-07

Hello,

In LPC17xx User manual (Section 4.10) it has been stated that :

"For system test and development purposes, any one of several internal clocks may be
brought out on the CLKOUT function available on the P1.27 pin, as shown in Figure 12."

Is there any problem if the CLKOUT function remains permanently ON to feed other parts as system clock ? I mean why manual has emphasized "For system test and development purposes" ?
Should I reconsider using CLKOUT @48MHZ as system clock ?

Sincerely,
Tech19

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Wed, 2012-08-08 13:57
#1
jdurand
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Joined: 2011-12-15

I've used CLKOUT on other processors to run other chips, but note that a 48MHz signal doesn't like to travel very far unless it's buffered and terminated.

It's not THAT high, but it's fast enough I'd worry about running more than one or two other chips and they should be physically close.

--
Jerry Durand, Durand Interstellar, Inc. www.interstellar.com
tel: +1 408 356-3886, USA toll free: 1 866 356-3886
Skype: jerrydurand

--
Jerry Durand, Durand Interstellar, Inc. www.interstellar.com
tel: +1 408 356-3886, USA toll free: 1 866 356-3886
Skype: jerrydurand

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Thu, 2012-08-09 23:20
#2
tech19
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Joined: 2012-08-07

Thanks for the feedback.

I can take care of the layout issues if I can use it. Actually I want to feed it to a CPLD which in turn will feed other components. The main issue is that I want a Sync clock with LPC. It is very convenient if I can use CLKOUT function as CPLD clock. My main worry is that maybe turning this function On may introduce unspecified problems.

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