Pullup Voltage on Wakeup Pin

[ASN7]

I am using an S32K314 on a custom board and would like to use the wakeup (WKPU) functionality. My requirement is for the MCU to wake up on a falling edge on pin PTA25. To achieve this, in the MEX configuration, I configured PTA25 as WKPU34 (with the offset applied; the corresponding hardware channel is 38). The pin is enabled and configured with an internal pull-up.

On the hardware side, only a multimeter is connected to PTA25—there are no other external components on this pin.

So I initially wanted to measure the voltage on this pin, so after Clock_Ip_Init and Siul2_Port_Ip_Init, the voltage measured on PTA25 is approximately 2.227 V. If I initialize SIUL2 only (without clock initialization), the voltage on the same pin measures about 5.102 V.

WKPU0_CLK is sourced from AIPS_SLOW_CLK, AIPS_SLOW_CLK is 40 MHz, SCS_CLK is set to PLL PHI0 which is at 160 MHz.
RTD Version:3.0.0 (S32K3_RTD_3_0_0_D2303_ASR_REL_4_7_REV_0000_20230331)
S32KDS Version:S32 Design Studio for S32 Platform, Version: 3.5, Build id: 240924 (Update 14)

How is the clock initialization affecting the pull-up voltage on PTA25? What could be causing this issue ?

[Julián_AragónM]

Hi @ASN7,

The pin PTA25 shares functionality with the OSC32K, as shown in the S32K314_IOMUX excel file:

PTA25	SIUL_MSCR25	0000_0000	GPI[25]	SIUL
	-	-	OSC32K_EXTAL	OSC32K	External Oscillator Input
	-	-	WKPU[34]	WKPU	Wakeup Input
	SIUL_IMCR533	0000_0010	EIRQ[5]	SIUL	External Interrupt
	SIUL_IMCR600	0000_0010	eMIOS_1_CH[8]_X	eMIOS_1	eMIOS Channel
	SIUL_IMCR632	0000_0010	eMIOS_2_CH[8]_X	eMIOS_2	eMIOS Channel
	SIUL_IMCR666	0000_0110	FXIO_D2	FXIO	FlexIO Bi-directional Shift/timer I/O

I have not tested the functionality, but this is most likely the root cause. Make sure to disable the oscillator, this can be checked in the OSCON bitfield in the SXOSC control register. It can also be reset manually with the following code line:

IP_SXOSC->SXOSC_CTRL &= ~SXOSC_SXOSC_CTRL_OSCON_MASK;

I think that when using the RTDs, SXOSC is enabled by default, so it has to be disabled.

Best regards,
Julián