Unlock flexible design with advanced PPS on PIC MCUs

In this tutorial, we will explore the Advanced Peripheral Pin Selections (PPS) feature available on various PIC microcontrollersIntroduction to PIC: Exploring the Basics of Microcontroller ArchitectureExplore the core principles of PIC microcontroller architecture, including Harvard design, RISC processing, and efficient memory organization.. PPS is a powerful capability that allows you to remap certain peripheral functions to different physical pins. By mastering PPS, you can significantly enhance flexibility in your project’s pin usage, making it simpler to customize your hardware layout.

Understanding What PPS Is🔗

• Peripheral Pin Select (PPS) is a configurable system that enables specific digital peripheral inputs and outputs (e.g., UART, SPI, PWM signals) to be linked to different pins than their default assignments. This flexibility can be particularly valuable when:

1. Specific pins are already reserved for other critical functions.

2. You want to optimize PCB layout by choosing more convenient pins.

3. The default pin mapping of a module does not match your design constraints.

Not all PIC devices incorporate PPS, so it’s essential to confirm whether your specific MCU supports it. Refer to your device datasheet for exact details and available remappable peripherals.

How PPS Works🔗

Modern PIC microcontrollersIntroduction to PIC: Exploring the Basics of Microcontroller ArchitectureExplore the core principles of PIC microcontroller architecture, including Harvard design, RISC processing, and efficient memory organization. that feature PPS typically include a set of Input Pin Select registers and Output Pin Select registers. These registers control the routing of peripheral inputs/outputs to the physical device pins. The general concept:

1. Input PPS: Maps a physical pin to the input of a peripheral (e.g., the RX line for a UART module).

2. Output PPS: Maps the output of a peripheral (e.g., a PWM or UART TX line) to a physical pin.

Each peripheral that supports PPS will have a unique identifier or code value. Similarly, each pin that can be remapped will have an identifier. By writing the appropriate code value to the respective PPS register, you complete the connection between a physical pin and the peripheral function.

Benefits of Using PPS🔗

1. Pin Optimization: Avoid unnecessary pin conflicts by flexibly assigning peripheral pins.

2. Simplified Hardware Layout: Position I/O lines in ways that minimize crossing on the PCB.

3. Easy Reusability: If a project demands a different arrangement, update the PPS configuration in code without redesigning the circuit.

4. Enhanced Feature Utilization: Freed-up default peripheral pins can be used as general-purpose I/O if needed.

General PPS Configuration Steps🔗

While the precise steps vary by device family and specific MCU, the typical procedure to configure PPS includes:

1. Unlock the PPS Registers: Many PIC MCUsMastering Digital I/O on PIC MCUs with Practical ExamplesLearn hands-on techniques for configuring and using digital I/O pins on PIC microcontrollers to control LEDs, sensors, and more in practical projects. protect critical registers with an unlock sequence. This ensures they are not inadvertently changed at runtime.

2. Write to the Output PPS Register: Assign a peripheral output (e.g., UART TX, PWM1, etc.) to a chosen remappable output pin.

3. Write to the Input PPS Register: Assign a peripheral input (e.g., UART RX, external interruptImplementing Interrupt-Driven Systems for Real-Time ApplicationsLearn to configure and optimize PIC microcontroller interrupts for real-time performance. Enhance responsiveness and efficiency using best practices.) to a chosen remappable input pin.

4. Lock the PPS Registers: Re-lock the PPS configuration to prevent accidental modifications.

5. Verify Configuration: Often you’ll test your setup by blinking an LED, sending test data over a serial port, or measuring a PWM output.

Below is a simplified illustration of a typical sequence in C using Microchip’s XC8 compilerGetting Started with MPLAB X and the XC8 CompilerSet up MPLAB X IDE and XC8 compiler for PIC programming with our comprehensive guide detailing installation, configuration, and debugging techniques.:

// Example for a hypothetical PIC device
// 1. Unlock PPS registers
PPSLOCK = 0x55;
PPSLOCK = 0xAA;
PPSLOCKbits.PPSLOCKED = 0;   // Now PPS registers are unlocked
// 2. Assign TX (a peripheral output) to a pin, e.g., RB6
RB6PPS = 0x14;  // Suppose '0x14' indicates TX function for your device
// 3. Assign RX (a peripheral input) to a pin, e.g., RB7
RXRXPPS = 0x0F; // Suppose '0x0F' indicates RB7 index for RX
// 4. Lock PPS registers
PPSLOCK = 0x55;
PPSLOCK = 0xAA;
PPSLOCKbits.PPSLOCKED = 1;   // PPS is now locked again

Note: The codes for the peripheral functions and pins vary by device. Always consult your MCU’s datasheet or reference manual for the correct values.

Common PPS Registers🔗

Below is a short sample table (fictitious codes shown as examples). In practice, your device datasheet will provide accurate values:

Advanced PPS Usage and Best Practices🔗

1. Check Datasheet Limits: Not all pins are remappable; some devices restrict which pins can handle certain signals.

2. Avoid Conflicts: Ensure you do not accidentally assign two different outputs to the same pin if it is not intended.

3. Plan Early: Integrate PPS assignments early in your design flow. This way, you can avoid multiple hardware revisions.

4. Use Clear Names: When writing code, rename registers or define constants to clearly indicate pin-function mappings.

5. Leverage Testing: Use development boards to experiment with different PPS arrangements before committing to a final design.

Example Use Case🔗

Imagine you need to free up a default UART TX pin for a high-current LED driver. PPS would allow you to:

1. Remap the UART’s TX line to a different, more convenient pin.

2. Preserve full UART functionality with your host PC interface.

3. Drive the LED from its original pin without re-engineering large parts of your circuit.

This type of reconfiguration can be performed quickly by changing a few lines in your embedded firmware, showcasing the convenience and flexibility offered by PPS.

Conclusion🔗

Peripheral Pin Select (PPS) is a powerful feature in various PIC microcontrollersIntroduction to PIC: Exploring the Basics of Microcontroller ArchitectureExplore the core principles of PIC microcontroller architecture, including Harvard design, RISC processing, and efficient memory organization. that elevates flexibility and customization in your embedded design. By enabling peripheral inputs and outputs to be remapped seamlessly, PPS simplifies hardware design and offers greater control over pin usage. Whether you are fine-tuning a design for an advanced project or simply optimizing your layout, understanding and leveraging PPS is an essential skill on the path from PIC beginner to PIC expert.

• With PPS in your toolkit, you can confidently design more efficient and adaptable PIC-based systems-achieving precisely the pin layout you envision.