LPC55xx ADC external trigger

[_Ferrari_]

Dear all,

I read in the LPC5526JBD100_User_Manual_11126 UM11126 manual that AD conversion can be trigger using external pins

I'm sorry but, since I'm new in NXP world, I can't understand if there are two dedicated pins or any GPIO pin can be used.

could you help me to solve the question ?

Thank you very much for your help and cooperation

regards

[_Ferrari_]

Ok, thank you

regards

[frank_m]

I suppose you will need to read the user manual in detail, especially the ADC section.
I don't use a LPC55xx, but assume it is not different than on other LPC MCUs.

An external trigger requires physical connection from the GPIO to the ADC peripheral on the silicon, thus there are usually only one or two pins to select from. Which one's can usually be found in the description of trigger source config register for the ADC peripheral.

By the way, I never really had the need to run the ADC using an external trigger.
Unless you require a very low jitter and delay, you could use a timer as trigger, and "gate" the results with the external trigger. Which means, either use or discard the ADC values depending on the gate input.
The advantage would be a more consistent timing (assuming interrupts).

[_Ferrari_]

Dear Frank,

thank you very much for your reply.

You wrote:

>I suppose you will need to read the user manual in detail, especially the ADC section.

I read the ADC setction but I noticed only the table that you chan see in the attached file.

So I suppose that, since the LPC55xx can handle up to 8 externa interrupt, only the first two (0 and 1) can be used as external ADC trigger. Of course they can routed to several phisical external pin.

Could you confirm if I'm rigth ?

you also wrote:

>By the way, I never really had the need to run the ADC using an external trigger.
>Unless you require a very low jitter and delay, you could use a timer as trigger, and "gate" the results >with the external trigger. Which means, either use or discard the ADC values depending on the gate i>nput.
>The advantage would be a more consistent timing (assuming interrupts).

Yes you are right. Unfortunately I have external asynchronous event

Thank you for very much for your help and cooperation

regards

[frank_m · Accepted solution]

> So I suppose that, since the LPC55xx can handle up to 8 externa interrupt, only the first two (0 and 1) can be used as external ADC trigger. Of course they can routed to several phisical external pin.

Here is the respective section in the LPC546xx user manual, a MCU I am using:

and:

I expect the LPC55 family to be very similiar in this regard.

> Yes you are right. Unfortunately I have external asynchronous event

Unless a jitter/delay of not more than a couple of nanoseconds is essential, I would go for a timer-triggered ADC conversion. Especially if it is not a single-shot conversion.
For the external asynchronous event, I would use ext. pin interrupt, and set a flag in the handler routine that enables the ADC conversion/storage.

But that depends on the exact project requirements that are unknown to me.