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iMXRT I/O pad configuration is underdocumented

Question asked by Udo Eberhardt on Mar 25, 2019
Latest reply on Mar 31, 2019 by fangfang



I'm having difficulties to understand I/O pad configuration details. The reference manual (rev 2) is not clear on that. Documentation is spread across two chapters:  Chapter 10 - IOMUX Controller (IOMUXC), and  Chapter 11 - General Purpose Input/Output (GPIO).

Specific questions:


Q1: IOMUXC_SW_PAD_CTL_* register fields PUE, PKE and PUS. How do these bits correlate? Is the following interpretation correct?

PKE=0  PUE=*  PUS=*   - output is plain, no keeper, no pullup/pulldown

PKE=1  PUE=0  PUS=*  - keeper is active, no pullup/pulldown

PKE=1  PUE=1  PUS=*  - no keeper, pullup/pulldown active according to PUS


Q2: OMUXC_SW_PAD_CTL_* register fields SPEED and SRE. How do these settings correlate? According to Figure 11-3 both settings configure the output driver. The reference manual does not have more details. The data sheet refers to slew rate settings only.