Application NoteNxp

Configuring and Using the Phantom Port Feature on the MPC5668

Application note for expanding the MPC5668 microcontroller's output pins by up to 116 using the Phantom Port feature and external shift registers via DSPI modules.

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Overview

This application note explains how to utilize the Phantom Port feature on the NXP MPC5668 microcontroller to add up to 116 extra General-Purpose Output (GPO) pins. By leveraging the Deserial-Serial Peripheral Interface (DSPI) modules and the System Integration Unit (SIU), the MCU can automatically transmit port values to external shift registers without CPU overhead. The document details hardware implementation using Fairchild MM74HC594 shift registers, including chaining multiple registers for 32-bit port expansion. Software configuration steps are provided for pin multiplexing, DSPI module initialization in DSI mode, and SIU logic setup to enable seamless port operation.

Use Cases

Expanding microcontroller output pin count for complex systems
Implementing low-cost GPIO expansion without CPU overhead
Interfacing MPC5668 with external shift registers for high-density signal control
Automotive or industrial control designs requiring high output pin counts

Topics

MPC5668

Phantom Port

DSPI

GPIO expansion

Shift Register

MM74HC594

SIU

Deserial-Serial Peripheral Interface

NXP

Freescale

Referenced Parts

MM74HC594

Fairchild

four Fairchild MM74HC594 ‘8-bit Shift Register with Output Registers’ were selected

MPC5668

Freescale Semiconductor

The Phantom Port feature on the MPC5668 microcontroller facilitates a low-cost solution

MM74HC594	Fairchild	four Fairchild MM74HC594 ‘8-bit Shift Register with Output Registers’ were selected
MPC5668	Freescale Semiconductor	The Phantom Port feature on the MPC5668 microcontroller facilitates a low-cost solution