How to output 32768Hz external crystal LFCLK at a GPIO pin?

RE: How to output 32768Hz external crystal LFCLK at a GPIO pin?

Yashur — Thu, 28 Sep 2017 06:24:33 GMT

what if i need a software solution to this?

RE: How to output 32768Hz external crystal LFCLK at a GPIO pin?

Jay Tyzzer — Thu, 23 Jan 2014 01:01:05 GMT

Yes,

You may connect an External 32khz Osc to the device.

Pin #46 XL1 Connection for 32.768 kHz crystal or external 32.768 kHz

RE: How to output 32768Hz external crystal LFCLK at a GPIO pin?

Hung Bui — Wed, 15 Jan 2014 13:08:55 GMT

Hi Buergervrm,

As Syntroniks already suggested, you can tap the XL2 and get the crystal signal from there. If your sensor need a crystal clock signal, you should be fine. If your sensor expect to have full swing clock signal then you may need to buffer the signal.

The other solution is good also. You can feed the XL1 with external 32768kHz from external oscillator and leave XL2 open. This has been described at section 12.1.1 in the nRF51 Series Reference.

RE: How to output 32768Hz external crystal LFCLK at a GPIO pin?

bvrm — Wed, 15 Jan 2014 10:54:54 GMT

So no more reply on this means it is not possible?

Further question: Could i feed in a 32768Hz square wave clock signal (from an oscillator) and use this as clock source for LFCLK (bypassing the nrf internal oscillator). The square wave clock signal from the external oscillator and drive both the nrf and sensor in sync.

RE: How to output 32768Hz external crystal LFCLK at a GPIO pin?

bvrm — Mon, 13 Jan 2014 10:49:50 GMT

XL1 and XL2 pins are designed to connect an external crystal which is the case in my hardware (nRF51822 EK atm). I think this pins should not be touched when there is a external crystal connected to not affect the internal oscillator loop.

Otherwise my sensor needs a square wave clock signal.

This is the first time i'm using an ARM, but i know from other MCU they could easily output the CPU system clock and/or RTC clock signal at a pin, which is very useful.

RE: How to output 32768Hz external crystal LFCLK at a GPIO pin?

syntroniks — Fri, 10 Jan 2014 19:31:14 GMT

XL2 which is pin 45 of the QFN48 package is designated as an analog output which is one of the connections to a low frequency crystal.

I do not know how much loading you can place on this pin (I assume very little) but perhaps a buffer could be attached to that pin. Alternatively, build the feedback circuit yourself and feed the nrf chip via its XL1 pin as an external reference.

Of course prototype before committing since with too much loading, the xtal might not start up.