Pros and Cons of using IRC for BASE_M4_CLK input

[cpchen]

Dear All, 

LPC4370 user manual sec. 13.2.1.1 detail steps of using crystal osciilator to change BASE_M4_CLK to higher than 110MHz,  my questions is following  

1. Can we use IRC osciilator for the same  purpose ? 

2. What are the pros and cons of using IRC vs crystal ocs for above putpose ? 

Appreciate anyone can help me clarify above questions.  

CP 

[bernhardfink]

There is no need to change over from IRC source to the crystal source when running above 110MHz.

But normally there is a crystal, because of the higher accuracy, required for USB 2.0, for audio, etc. That's why there is this example in the user manual.

The IRC and the crystal are just 12MHz sources, that's the important information here. When the user manual says "run from the IRC" or "run from crystal" then this just means that the chip runs on a 12MHz clock. If you put the PLL in place, then the PLL is sourced from the 12MHz, but the chip (or part of the chip) runs on the PLL output clock.

Regards,

Bernhard.

[cpchen]

Hi Bernhard,  thanks for the clarification !

Regards,

CP