Possible to use K64F XTAL0 as GPIO

[aberger]

Is it possible to use the XTAL0 pin on the K64F as a GPIO? The pinout table found on the K64F Sub-Family Data Sheet suggests that configuring the pin as ALT1 should allow for this, by configuring it as PTA19. However in the footnotes under Table 19 (pg 29) of the same document it states:

The EXTAL and XTAL pins should only be connected to required oscillator components and must not be connected to any other device.

And then in the K64 Reference Manual, under 26.6 External Clock Connections it states:

XTAL can be used as a GPIO when the GPIO alternate function is configured for it.

So which am I to believe?

When providing an external clock input to EXTAL0, should XTAL0 be grounded (that is, as opposed to using EXTAL0 and XTAL0 to drive a crystal oscillator)? It appears there is an inverter between EXTAL0 and XTAL0 that would draw large currents if XTAL0 is shorted to ground. Or is this inverter disabled when some Oscillator Register is disabled?

[jingpan]

Hi Andy,

The footnote in datasheet is talk about test condition. If this pin is used as XTAL, nobody will connect it to other function. If you use internal clock source, you can use it as a normal gpio.

When PTA18 is work as external clock input, you can still use PTA19. They are different path.

Regards,

Jing