Understanding different communication/storage interfaces of an MCU

MIPI (Mobile Industry Processor Interface)

is a set of standards developed by the MIPI Alliance for interfaces in mobile devices and other hardware components. These standards are widely used to ensure interoperability and to streamline the design and development process of various components such as cameras, displays, sensors, and processors. 

https://mixel.com/ip-cores/mipi-cores/

Some of the key MIPI specifications include: (Ref: https://mixel.com/mipi-m-phy-takes-center-stage/)

• MIPI CSI-2 (Camera Serial Interface 2): Used for interfacing cameras with host processors. It enables high-speed image data transfer from camera sensors to processors.

• MIPI DSI (Display Serial Interface): Used for connecting displays to host processors, allowing for efficient and high-speed data transfer to display panels.

• MIPI I3C (Improved Inter Integrated Circuit): A communication interface that combines the best features of I2C and SPI, designed for connecting sensors and other peripherals.

• MIPI C-PHY and D-PHY: Physical layer standards that provide high-speed data transfer capabilities. C-PHY uses a three-phase encoding scheme, while D-PHY uses a differential signaling scheme. MIPI C-PHY and MIPI D-PHY are physical layer (PHY) standards defined by the MIPI Alliance. These specify how bits are physically transmitted over wires, especially for MIPI CSI-2 (camera interface) and MIPI DSI-2 (display interface). They differ in signaling method, performance, and pin efficiency.

  

  https://mixel.com/mipi-c-phy-d-phy-overview-jp/

• MIPI D-PHY 
• Type: High-speed differential signaling (similar to LVDS) 
• Wires per lane: 2 wires (differential pair) per data lane + 2 wires for clock (1 pair)
• Data Rate: Up to ~4.5 Gbps per lane (latest spec, version-dependent)
• Structure:
• 1 clock lane (mandatory)
• 1 to 4 (or more) data lanes
• Voltage signaling: Differential (low swing, high speed)
• Advantages:
• Mature, widely adopted (used in most current smartphones)
• Simpler to design/test than C-PHY 
• Used in both CSI (Camera) and DSI (Display) interfaces

• MIPI C-PHY
• Type: Three-wire (trio) encoding with multi-level signaling
• Wires per lane: 3 wires (called a trio) encode 3 bits per symbol
• Data Rate:Up to 6.0 Gsps per trio
• Effective throughput is up to 2.28 Gbps per wire (because 3 bits are encoded per 3 wires)
• Structure:
• Uses trios instead of differential pairs
• More efficient in terms of data rate per wire.

• MIPI RFFE (RF Front-End Control Interface): A standard for controlling RF front-end components such as power amplifiers, antenna tuners, and filters in mobile devices.

• MIPI UniPro (Unified Protocol): A transport layer protocol designed for high-speed data communication between integrated circuits within a device.

• MIPI SLIMbus (Serial Low-power Inter-chip Media Bus): A standard for transporting audio and control data between components.

MIPI (Mobile Industry Processor Interface) standards are designed to meet the specific needs of mobile and other low-power, high-performance applications. 

Comparing MIPI with existing protocols like USB and UART highlights its unique advantages and use cases.

Advantages of MIPI

1. Low Power Consumption: MIPI interfaces are designed to be power-efficient, which is essential for mobile and battery-powered devices.
2. High Performance: MIPI standards support high data transfer rates, making them suitable for high-resolution cameras, high-definition displays, and fast sensors.
3. Scalability: MIPI standards are scalable, supporting a wide range of data rates and configurations to meet the needs of different devices and applications.
4. Interoperability: MIPI standards ensure interoperability between components from different manufacturers, simplifying the design and integration process.
5. Compact Design: MIPI interfaces use fewer pins and smaller connectors, allowing for more compact and streamlined device designs.

For a detailed explanation on this topic, you can watch the video on YouTube.

MIPI vs. USB

USB (Universal Serial Bus) is a standard designed for connecting peripherals to a host computer. It is widely used for its simplicity and versatility.

Key Features of USB:

• Plug and Play: Easy to connect and disconnect devices.
• Data Transfer Rates: Supports multiple versions with varying speeds (e.g., USB 2.0 up to 480 Mbps, USB 3.0 up to 5 Gbps, USB 3.1 up to 10 Gbps).
• Power Supply: Can provide power to connected devices (e.g., USB 2.0 provides up to 500 mA, USB 3.0 up to 900 mA).
• Universal Compatibility: Supports a wide range of devices and operating systems.

Advantages of MIPI over USB:

• Optimized for Mobile Devices: MIPI standards are specifically designed for mobile devices, focusing on low power consumption and high performance, which are crucial for battery-powered devices.
• High Efficiency: MIPI interfaces, such as MIPI CSI-2 and DSI, are highly efficient in terms of data transfer rates and power consumption, making them ideal for camera and display interfaces in mobile devices.
• Compact and Flexible: MIPI standards support high-speed data transfer with fewer pins and smaller connectors, which is beneficial for the compact and space-constrained designs of mobile devices.

MIPI vs. UART

UART (Universal Asynchronous Receiver/Transmitter) is a protocol used for asynchronous serial communication between devices.

Key Features of UART:

• Simple Interface: Uses only a few wires (typically TX, RX, and ground) for communication.
• Low Data Rates: Typically used for lower-speed communication (e.g., 9600 to 115200 bps).
• Asynchronous Communication: Does not require a shared clock signal, making it simple to implement.

Advantages of MIPI over UART:

• High Data Rates: MIPI interfaces can handle much higher data rates compared to UART. For example, MIPI CSI-2 can transfer data at rates up to several Gbps, while UART is limited to much lower speeds.
• Targeted Use Cases: MIPI standards are designed for specific use cases such as camera, display, and sensor interfaces, offering optimized performance for these applications.
• Synchronous Communication: MIPI protocols typically use synchronous communication, which allows for more reliable and higher-speed data transfer.

DVP Interface

DVP (Digital Video Port) is an interface primarily used for transmitting video data from camera modules to processing units like microcontrollers or processors. It is a parallel interface, which means it transmits multiple bits of data simultaneously across multiple lines.

Key Features of DVP:

1. Parallel Data Transmission: Typically 8 to 12 data lines are used for transmitting video data, along with additional lines for control signals (e.g., VSYNC, HSYNC, PCLK).
2. Simplicity: Easier to implement compared to high-speed serial interfaces; often used in simpler or low-cost designs.
3. Lower Data Rates: Generally supports lower data rates compared to MIPI interfaces.
4. Less Power Efficient: Higher power consumption compared to serial interfaces like MIPI due to the parallel nature of data transmission.
5. Shorter Transmission Distance: More suitable for short-distance communication within a device due to signal integrity issues over longer distances.

Comparison: DVP vs. MIPI

1. Data Transmission Method

• DVP: Parallel interface with multiple data lines transmitting simultaneously. Simpler but less efficient.
• MIPI CSI-2: High-speed serial interface with fewer lines transmitting data serially. More efficient and supports higher data rates.

2. Data Rates

• DVP: Typically supports lower data rates. Suitable for lower resolution or frame rate requirements.
• MIPI CSI-2: Supports much higher data rates, making it ideal for high-resolution and high-frame-rate applications.

3. Power Consumption

• DVP: Generally higher power consumption due to more signal lines switching simultaneously.
• MIPI CSI-2: Lower power consumption, which is crucial for battery-powered devices like smartphones and tablets.

4. Complexity

• DVP: Simpler and easier to implement. Often used in lower-cost or less complex designs.
• MIPI CSI-2: More complex due to high-speed signaling and differential pairs but offers better performance.

5. Transmission Distance

• DVP: Suitable for short-distance communication within a device. Signal integrity degrades over longer distances.
• MIPI CSI-2: Better suited for longer distances within a device due to differential signaling and reduced susceptibility to noise.

1. LVDS – Low-Voltage Differential Signaling

LVDS is a high-speed, low-power digital signaling standard that transmits data over differential pairs.

• Type: Differential digital signaling

• Voltage: ~350 mV swing

• Speed: Up to 3 Gbps (varies)

• Use Case: LCD panels, camera modules, internal chip-to-chip links

• Advantages:

  • Low power consumption

  • High noise immunity

  • Minimal electromagnetic interference (EMI)

Typical Applications:
FPD-Link (Flat Panel Display Link), Camera Serial Interface (CSI), Display Serial Interface (DSI)

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2. SLVS – Scalable Low-Voltage Signaling

SLVS is a more advanced differential interface used for very high-speed applications, particularly where LVDS falls short.

• Type: High-speed serial differential signaling

• Voltage: ~200 mV

• Speed: >5 Gbps per lane

• Use Case: CMOS image sensors, high-resolution cameras, industrial vision

• Advantages:

  • Higher speed than LVDS

  • Lower power per bit

  • Excellent signal integrity

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3. FPD – Flat Panel Display Interface

FPD, particularly FPD-Link, refers to a family of interfaces designed for connecting display controllers to panels.

• Type: LVDS-based (often)

• Variants:

  • FPD-Link I/II: Legacy LVDS connections

  • FPD-Link III: High-speed video/audio/control over single coax or STP

• Use Case: Automotive infotainment systems, industrial monitors

• Advantages:

  • Supports video, audio, and control in one cable

  • Highly robust against interference

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4. CVBS – Composite Video Baseband Signal

CVBS is an analog video signal that combines all image components into a single line — a standard for legacy video systems.

• Type: Analog, single-ended

• Resolution: Standard Definition (480i / 576i)

• Use Case: CCTV, analog TVs, VCRs

• Signal: Combines luminance, chrominance, and sync

• Advantages:

  • Simple wiring

  • Broad compatibility

• Disadvantages:

  • Susceptible to noise

  • Poor image quality compared to digital standards

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5. SSI – Synchronous Serial Interface

SSI is a digital interface used in industrial control systems, particularly for absolute encoders.

• Type: Synchronous, half-duplex

• Signals: Clock (CLK), Data (DATA)

• Use Case: Motion control, servo drives, encoders in automation

• Advantages:

  • Noise-immune (often RS-422 differential)

  • Deterministic communication (critical for control loops)

• Speed: Moderate (~100 kHz–1 MHz), not meant for high-throughput

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6. SPI – Serial Peripheral Interface

SPI is a widely used full-duplex synchronous protocol used to communicate between microcontrollers and peripherals.

• Type: Full-duplex serial communication

• Signals: SCLK, MOSI, MISO, SS

• Use Case: Flash memory, sensors, ADC/DAC, displays

• Advantages:

  • Fast and simple

  • Multi-slave support with chip-select lines

• Disadvantages:

• No built-in error checking

• Point-to-point; limited bus length

What is SD?

SD (Secure Digital) is a memory-specific interface designed for data storage.

• Purpose: Mass storage (memory cards)

• Bus Type: Serial (1-bit or 4-bit modes)

• Voltage: 3.3V (standard), 1.8V (UHS modes)

• Speed Classes:

  • Standard SD: Up to 25 MB/s

  • SDHC, SDXC: Up to 104 MB/s (UHS-I), >300 MB/s (UHS-II/III)

• Use Cases:

  • Cameras, smartphones, embedded Linux boards

  • File-based storage (FAT32, exFAT)

✅ Typical Feature: Supports only memory devices

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📗 What is SDIO?

SDIO (Secure Digital Input Output) extends the SD interface to support non-storage devices, effectively acting as a high-speed serial bus for peripherals.

• Purpose: Interface for I/O peripherals (not storage)

• Examples:

  • Wi-Fi / Bluetooth modules

  • GPS receivers

  • Barcode scanners

• Bus Type: Same as SD (1-bit or 4-bit serial)

• Speed: Same as SD (depends on mode), up to 50–100 Mbps typical

• Mode: Can support Interrupts, Direct Memory Access (DMA)

✅ Bonus: Some SDIO devices support memory + I/O combo (e.g., Wi-Fi with onboard flash)

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Interface : NFC – Near Field Communication

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Type      : Short-range wireless communication (RF, 13.56 MHz)

Signals   : No direct signals; operates via magnetic field coupling

Use Case  : Contactless payments, access control, pairing, asset tagging

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Advantages:

  • Very low power (supports passive tags)

  • Secure short-range operation

  • Peer-to-peer and card emulation modes

Disadvantages:

  • Very short range (<10 cm)

  • Low data rates (max ~424 kbps)

  • Limited to small data transfers

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