MCU Boot Mode Selection Using One GPIO Pin and Resistor States

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Solution Overview

Problem

Microcontroller units (MCUs) face limitations in selecting boot modes due to a limited number of General Purpose Input/Output (GPIO) pins, which restricts the number of available commands and contradicts the need for minimizing pin usage.

Innovation Solution

A system and method that utilize external pull-up and pull-down resistors, along with a control logic, to configure a single input pin to provide multiple boot options by setting logic levels, including a floating state, allowing for increased command selection without increasing the number of input pins.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the number of input pins is increased to provide more boot options, then the number of selectable commands increases, but the number of GPIO pins required increases

Engineering Contradiction:

Improvenumber of boot optionsVSAvoidnumber of GPIO pins

Core Design Contradiction:

Adaptability or versatilityVSQuantity of substance

Solution Approach 1:

The patent changes the electrical state parameters of a single pin by using external pull-up and pull-down resistors to create multiple stable states (high impedance, pulled high, pulled low). This allows one pin to represent multiple boot options (0, 1, 2, 3) by detecting which resistor configuration is active, thereby increasing adaptability without increasing pin quantity

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

External pull-up and pull-down resistors are introduced as intermediary components between the single input pin and the boot mode selection logic. These resistors mediate the relationship between the pin's electrical state and the desired boot mode, enabling multiple selectable commands through a single pin by creating distinct voltage states that the MCU can detect

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of manufacture

If the number of GPIO pins is minimized to reduce space occupation and costs, then space occupation and costs decrease, but the number of available boot options decreases

Engineering Contradiction:

Improvespace occupation and costsVSAvoidnumber of boot options

Core Design Contradiction:

Ease of manufactureVSAdaptability or versatility

Solution Approach 1:

A single input pin is made multi-functional by combining it with external pull-up and pull-down resistors. The pin can serve multiple boot selection functions (representing 4 different boot modes) instead of being limited to a single binary state, thereby maintaining ease of manufacture with minimal pins while preserving adaptability through multiple boot options

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS11705904B2System and method for selecting an operating mode, such as a boot mode, of a micro-controller unit

Publication Date: 2023.07.18 STMICROELECTRONICS SRL

AI summary

A microcontroller includes an input pin and internal pull-up and pull-down circuits. External pull-up and pull-down circuits are also coupled to the input pin. The microcontroller is operable according to different configuration modes which include configuring the input pin in a floating state. A control logic then configures the internal pull-up and pull-down circuits according to an internal pull-up mode to acquire a first input voltage signal (at a first logic value) from the input pin, and further configure the internal pull-up and pull-down circuits according to an internal pull-down mode to acquire a second input voltage signal (at a second logic value) from the input pin. A selection of the operating mode of the MCU is then made based on the acquired first and second logic values.