topic Re: Can I verify external 50 MHz crystal with LPC540? in LPC Microcontrollers

Can I verify external 50 MHz crystal with LPC540?

jana_beck — Mon, 16 Mar 2020 18:15:17 GMT

Hi!
I am currently working on setting up a functional test for my application.
For one of the components I need a 50 MHz clock signal.
Is it possible to measure if this clock signal is correct using my MCU (LPC54016JBD100).

I am not very familiar with internal clocks, any help appreciated!

Re: Can I verify external 50 MHz crystal with LPC540?

ZhangJennie — Thu, 19 Mar 2020 10:23:20 GMT

HI Jana

We can measure CLKOUT pin to check internal clock.

Using CLKOUTSELA to set the clock source.

Below diagram, main_clk can be measured by CLKOUT pin.

Hope this helps,

Jun Zhang

Re: Can I verify external 50 MHz crystal with LPC540?

jana_beck — Fri, 20 Mar 2020 02:11:00 GMT

Hi Jun,
thank you for the reply.
I am actually trying to do it the other way around, having an external clock (which is only used by another component, to be precise by a PHY) and verifying if the clock signal is correct with the MCU.

I am trying to have a functional test for my electronic assembly with as much measurements done using the MCU.

Re: Can I verify external 50 MHz crystal with LPC540?

ZhangJennie — Mon, 23 Mar 2020 03:39:25 GMT

You want to use LPC to measure an external 50MHz clock.

The idea is to use input capture feature to measure 50M pin. each toggle trigger a capture_counter+1.

You need also have an accurate external low frequency clock (Don't use internal FRO, it has 1% error), for example 100KHz, it trigger interrupt for each clock. then you can calculate "capture_counter" value.

the measured clock = 100Khz * capture_counter value

Have a nice day

Jun Zhang