MISO pin internal pullup in SPI configuration

Question

Hi, 
 I would like to activate internal pullup of MISO pin in SPI configuration. 
 I used below before configuring SPI function as: 
 
 mxc_gpio_cfg_t miso_pin22 ; 
 miso_pin22 . port = MXC_GPIO0 ; // PORT0 
 miso_pin22 . mask = MXC_GPIO_PIN_22 ; // PIN0_22 (MISO) 
 miso_pin22 . func = MXC_GPIO_FUNC_ IN, ALT1 to ALT4 ; // Changed here as IN, ALT1, ALT2, ALT3 and ALT4 
 miso_pin22 . pad = MXC_GPIO_PAD_PULL_UP ; // 
 miso_pin22 . vssel = MXC_GPIO_VSSEL_VDDIOH ; // 3.3V I/O 
 miso_pin22 . drvstr = MXC_GPIO_DRVSTR_0 ; // 
 MXC_GPIO_Config ( & miso_pin22 ); // 
 
 After of this, I configured the MCU as SPI function but pullup can not be activated. 
 How can I activate an internal pullup of MISO pin? 
 
 Please advise.

HalukKirkgoz · Accepted Answer

Hi Satoru, 
 On MAX32xxx devices, the weak and strong pull-ups are controlled within the GPIO pad block. Many of the SPI initialization helpers internally invoke MXC_GPIO_Config() for their pin mapping, which typically resets the pad configuration to its default state (i.e., no pull-up or pull-down). As a result, if a pull-up is configured prior to calling MXC_SPI_Init() , the driver will overwrite those pad settings. 
 To address this, please proceed as follows:

Retain the MXC_SPI_Init() call as is.

Immediately after invoking it, apply a one-pin override for MISO in its SPI alternate function. Specifically, use MXC_GPIO_FUNC_ALT1 for SPI1_MISO on P0.22 .

// 1) Bring up SPI first
MXC_SPI_Init(MXC_SPI0, 1, 0, 0, 0, /*... your args ...*/);

// 2) Re-apply pad config for MISO in its ALT function
mxc_gpio_cfg_t miso = {
 .port = MXC_GPIO0,
 .mask = MXC_GPIO_PIN_22, // P0.22 = SPI1 MISO pin
 .func = MXC_GPIO_FUNC_ALT1, // the exact ALT for SPI1 MISO on P0.22
 .pad = MXC_GPIO_PAD_PULL_UP, // weak pull-up enabled
 .vssel = MXC_GPIO_VSSEL_VDDIOH, // if that pad is on the 3.3V bank
 .drvstr = MXC_GPIO_DRVSTR_0,
};
MXC_GPIO_Config(&miso); 
 This approach remains robust even if you re-initialize SPI at a later point&mdash;simply re-apply the one-line override after each initialization. 
 Kind regards, 
 Haluk)

Popular Forums

Product Forums

Application Forums

Design Center Forums

Highlighted Webinar

Places

Libraries

Upcoming Learning & Events

Challenge Yourself!

What's Brewing

Places

Resources

Visit ContentZone

The Latest Read

New Release

Recent Technical Insights

Forums

Learn

Community Hub

ContentZone

Products Mentioned

Associated Drivers

Thread Details

MISO pin internal pullup in SPI configuration

Thread Summary

Before You Switch