topic LPC17xx ClkOut function as system clock in LPC Microcontrollers

LPC17xx ClkOut function as system clock

lpcware — Wed, 15 Jun 2016 17:33:14 GMT

Content originally posted in LPCWare by tech19 on Wed Aug 08 00:06:42 MST 2012
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

Re: LPC17xx ClkOut function as system clock

lpcware — Wed, 15 Jun 2016 17:33:15 GMT

Content originally posted in LPCWare by jdurand on Wed Aug 08 13:57:17 MST 2012
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.

Re: LPC17xx ClkOut function as system clock

lpcware — Wed, 15 Jun 2016 17:33:16 GMT

Content originally posted in LPCWare by tech19 on Thu Aug 09 23:20:34 MST 2012
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.