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COM Express
COM Express
COM Express
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COM Express Type 6 Module VIA COMe-8X92 with VIA Nano X2
COM Express Carrier Board

COM Express is a form factor for computer-on-modules (COMs), which are highly integrated and compact computers that can be used in design applications much like integrated circuit components. Each module integrates core CPU and memory functionality, the common I/O of a PC/AT, USB, audio, graphics (PEG), and Ethernet. All I/O signals are mapped to two high density, low profile connectors on the bottom side of the module. COM Express employs a mezzanine-based approach. The COM modules plug into a baseboard that is typically customized to the application. Over time, the COM Express mezzanine modules can be upgraded to newer, backwards-compatible versions. COM Express is commonly used in Industrial, military, aerospace, gaming, medical, transportation, Internet of things, and general computing embedded applications.

History

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The COM Express standard was first released in 2005 by the PCI Industrial Computer Manufacturers Group (PICMG).[1] It defined five module types, each implementing different pinout configurations and feature sets on one or two 220-pin connectors. It also defined 2 module sizes (later expanded to 4) to serve more applications while maintaining compatibility within each module type.[2] COM Express is used in railway, industrial, and military applications. There are also efforts for a Rugged COM Express specification through VITA.

Types

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There are 8 different pin outs defined in the specification. The most commonly used pin outs are Type 6 and Type 10. The latest pin-out added in revision 3.0 of the COM Express specification (available from www.picmg.org) is Type 7. The Type 7 provides up to four 10 GbE interfaces and up to 32 PCIe lanes, making COM Express 3.0 appropriate for data center, server, and high-bandwidth video applications. COM Express Rev 3.0 removed legacy Type 1, Type 2, Type 3, Type 4, and Type 5, recommending that new designs should use Type 6, 7 or 10.[3]

Maximum available interfaces for the defined types:

Type Connectors PCI Express lanes PEG PCI IDE SATA LAN Video Serial Other features Note
1 AB (Single) 6 No No No 4 1 LVDS A & B, VGA Legacy
2 AB & CD (Double) 22 Yes Yes 1 4 1 LVDS A & B, VGA, PEG/SDVO Legacy
3 AB & CD (Double) 22 Yes Yes No 4 3 LVDS A & B, VGA, PEG/SDVO Legacy
4 AB & CD (Double) 32 Yes No 1 4 1 LVDS A & B, VGA, PEG/SDVO Legacy
5 AB & CD (Double) 32 Yes No No 4 3 LVDS A & B, VGA, PEG/SDVO Legacy
6 AB & CD (Double) 24 Yes No No 4 1 LVDS A & B, VGA, 3 x DDI (*2) 2 TX/RX serial pairs with option to overlay CAN interface on 1 port 4x USB 3.0

8x USB 2.0

7 AB & CD (Double) 32 Yes, for 16 lanes. Yes No 2 1 + 4x 10G KR None 2 TX/RX serial pairs with option to overlay CAN interface on 1 port 4x USB 3.0

4x USB 3.0

Added in Rev 3.0[3]
10 AB (Single) 4 No No No 2 1 LVDS A only (AB (Single) channel), DDI (*2) 2 Serial COM, 1 optional CAN USB 3.0 (*1)

(*1) Option on previously allocated SATA2 and SATA3 pins. Implementor specific. [4]

(*2) DDI can be adapted to DisplayPort, HDMI, DVI or SDVO (legacy, no longer supported for types 6, 7 and 10) in the carrier board. [5]

Legend: PEG - PCI Express Graphics. Legacy - not recommended for new designs.

Size

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The specification defines 4 module sizes:

COM Express has 4 form factors. See the PICMG COM Express specification for carrier board mounting positions.
  • Mini: 55 × 84 mm (2.2 × 3.3 in)
  • Compact: 95 × 95 mm (3.7 × 3.7 in)
  • Basic: 95 × 125 mm (3.7 × 4.9 in)
  • Extended: 110 × 155 mm (4.3 × 6.1 in)

Specification

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The COM Express specification is hosted by PICMG. It is not freely available but a paper copy may be purchased for $150USD from the PICMG website.[3] However, the COM Express Design Guide is free to download.

The original revision 1.0 was released July 10, 2005. Revision 3.0 (PICMG COM.0 R3.0) was released in March 2017.[6][3] COM Express also specifies an API to control embedded functionalities like watchdog timer or I2C. This is a separate document which is freely available (EAPI 1.0).

It also defines a carrier board eeprom to hold configuration information. This is also a separate and free available document (EeeP R1.0).

See also

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References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

COM Express

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from Grokipedia
COM Express is a modular specification for computer-on-module (COM) hardware, defining standardized, compact single-board computers that integrate core processing elements such as CPUs, , and I/O interfaces onto a swappable module that mounts onto a customizable carrier board. Developed by the PCI Industrial Computer Manufacturers Group (PICMG), it enables rapid design cycles and upgrades in embedded systems by separating the fixed compute module from application-specific peripherals on the carrier. Ratified in 2005 as PICMG COM.0, the standard has undergone three major revisions, with the latest—Revision 3.1 released in summer 2022—adding support for high-speed interfaces like PCIe Gen 4, USB 4.0, and MIPI-CSI for enhanced performance in modern applications. It defines eight module types (with Types 6, 10, and 7 being prominent in recent revisions) tailored to varying power and I/O needs, such as graphics-intensive (Type 6) or server-oriented (Type 10) configurations. Four form factor sizes accommodate diverse use cases: Mini (84 mm × 55 mm) for space-constrained devices, Compact (95 mm × 95 mm) for balanced performance, Basic (125 mm × 95 mm) for general embedded computing, and Extended (155 mm × 110 mm) for higher integration demands. Widely adopted in industries like industrial automation, medical devices, transportation, and , COM Express promotes interoperability among vendors by standardizing pinouts, electrical interfaces (including up to 440 pins), and protocols like SPI and GPIO, reducing development costs and time-to-market compared to fully custom designs. A forthcoming Revision 3.2 aims to further evolve the standard for emerging technologies, building on its legacy as the leading COM form factor in the embedded market.

Overview

Definition

COM Express is a standardized specification for computer-on-modules (COMs), developed and maintained by the PCI Industrial Computer Manufacturers Group (PICMG). It defines a family of modular, small form factor embedded computing modules designed primarily for mid-range edge processing and networking applications. These modules integrate core computing elements such as processors, memory, and essential logic onto a compact board that plugs into a custom carrier board, enabling flexible system design without requiring full custom motherboard development. The standard separates the compute-intensive components from application-specific peripherals, allowing designers to upgrade processing power independently while reusing carrier boards tailored to particular I/O requirements. This approach reduces engineering complexity, accelerates time-to-market, and supports scalability across performance levels, making COM Express a widely adopted solution in industrial, , transportation, and defense sectors. By standardizing the module's physical layout, electrical interfaces, and thermal management, it ensures among modules from different vendors. Key elements of COM Express include a high-speed edge connector supporting up to 440 pins across dual 220-pin interfaces, which facilitate data transfer rates suitable for modern embedded needs. The specification outlines four module sizes—Mini (84 mm × 55 mm), Compact (95 mm × 95 mm), Basic (125 mm × 95 mm), and Extended (155 mm × 110 mm)—to accommodate varying power and I/O demands while maintaining a consistent pinout for carrier compatibility. Thermal interfaces are also defined to ensure reliable operation in harsh environments, emphasizing passive cooling where possible.

Core Principles

COM Express operates on the fundamental principle of modularity, which separates the core computing functions—such as the processor, chipset, and main memory—onto a standardized computer-on-module (COM) that plugs into a customizable carrier board responsible for application-specific input/output (I/O) and connectivity. This architectural division allows system designers to develop and upgrade compute-intensive elements independently of peripheral interfaces, promoting flexibility in embedded and industrial applications. By encapsulating high-speed processing on the module, COM Express minimizes redesign efforts for evolving computational needs while enabling the carrier board to adapt to diverse end-user requirements, such as custom sensors or networking ports. A cornerstone of the specification is , ensuring and vendor independence through precisely defined pinouts, mechanical form factors, and electrical interfaces. The COM Express module connects to the carrier via a high-density 440-pin , supporting up to 220 differential pairs for serial signaling, which facilitates consistent integration across modules from different manufacturers. This extends to four module sizes— (84 mm × 55 mm), Compact (95 mm × 95 mm), Basic (125 mm × 95 mm), and Extended (155 mm × 110 mm)—and eight types. While eight types are defined, Types 1–5 are considered legacy; Types 6, 7, and 10 are prominent for new designs (e.g., Type 6 for graphics-intensive applications, Type 7 for , Type 10 for low-power server-oriented configurations), allowing selection based on performance and space constraints without altering carrier designs for compatible types. Electrical characteristics adhere to industry norms like and USB, with power delivery standardized at 5V or 12V to support efficient power states from S0 (full on) to S5 (soft off). The design philosophy emphasizes scalability and future-proofing by prioritizing high-bandwidth, serial-oriented interfaces over legacy parallel buses, aligning with modern embedded computing trends. For instance, Revision 3.1 (ratified in 2022) incorporates support for PCIe Gen 4 (up to x16 lanes), USB 4.0, and emerging standards like MIPI-CSI for , enabling modules to handle mid-range edge processing demands in sectors like medical devices and rugged networking. This approach reduces development time-to-market by up to 50% through component reuse and plug-and-play compatibility, as validated in PICMG guidelines, while thermal and mechanical standards—such as requirements and ESD protection—ensure reliability in harsh environments. Overall, these principles foster a where innovation focuses on application layers rather than reinventing core hardware.

History and Evolution

Development Timeline

The development of COM Express began in the early 2000s as part of efforts by the PCI Industrial Computer Manufacturers Group (PICMG) to standardize modular for embedded systems. The standard was initially ratified in 2005, with Revision 1.0 (PICMG COM.0 R1.0) released on July 10, establishing the core form factor for Computer-on-Modules (COMs) with a focus on x86-based processors and peripheral interfaces like Gen 1, , and USB 2.0. Building on initial adoption in industrial applications, PICMG formed a subcommittee in 2009 to address evolving peripheral needs, leading to Revision 2.0 (PICMG COM.0 R2.0), which was publicly released on August 30, 2010. This update introduced enhanced display support via LVDS and SDVO, faster Gen 2 lanes, and additional pinouts (Types 6 and 10) to accommodate graphics-intensive and server-oriented designs, while maintaining with earlier modules. A minor update followed with Revision 2.1 in 2012, refining electrical characteristics and carrier board design guidelines without major architectural changes, ensuring stability for ongoing implementations. The standard evolved further to support modern , culminating in Revision 3.0 (PICMG COM.0 R3.0), released on March 31, 2017. This version expanded to eight pinout types, including the new Type 7 for data-centric applications with 32 lanes, and introduced support for PCIe Gen 3, , and enhanced thermal management to meet demands in edge and IoT systems. Most recently, Revision 3.1 was ratified in summer 2022, updating Types 6, 7, and 10 to incorporate PCIe Gen 4, Gen 3, USB 4.0, MIPI-CSI 2, and SoundWire interfaces, enabling higher bandwidth for AI, , and applications while preserving the modular ecosystem's longevity. Revision 3.2 remains in development as of 2025, focusing on further peripheral updates for emerging server and client needs.

Major Revisions

The COM Express specification, developed by the PCI Industrial Computer Manufacturers Group (PICMG), was first ratified as Revision 1.0 in July 2005. This initial version established the foundational modular architecture for computer-on-modules (COMs), defining two module sizes—Basic (95 mm × 125 mm) and Extended (110 mm × 155 mm)—along with five pinout types (Types 1 through 5) tailored to x86-based embedded designs. It emphasized standardized interfaces such as PCI, LPC bus, IDE, USB 2.0, and legacy graphics outputs like LVDS and TV-Out, enabling rapid prototyping and customization in industrial applications while separating core compute from application-specific I/O on carrier boards. Revision , released in 2010, introduced significant enhancements to address evolving and storage needs. Key updates included a new Compact form factor for smaller footprints, the addition of pinout Types 6 (optimized for advanced with SDVO, LVDS, and support) and Type 10 (a reduced-pin variant of Type 1 for cost-sensitive designs). The specification removed TV-Out support, added SPI flash interfaces for firmware updates, and improved mechanical tolerances for better thermal management and connector reliability, while maintaining with Revision 1.0 modules. These changes expanded applicability to and -intensive embedded systems. In March 2017, PICMG ratified Revision 3.0, which extended COM Express into server-grade applications by introducing pinout Type 7. This type prioritized high-bandwidth server interfaces, such as up to 32 PCIe lanes (Gen 3), multiple 10 GbE ports, and , while omitting integrated graphics to support external GPUs or network-focused designs. The revision also formalized a Mini size (55 mm × 84 mm) for ultra-compact applications and enhanced power delivery up to 120 W, enabling "server-on-module" solutions for data centers and without hardware. It built on prior types for legacy support but emphasized for multi-core processors. Revision 3.1, ratified in summer 2022, further modernized the standard with support for emerging high-speed interfaces while ensuring with Revision 3.0 hardware. Notable additions included PCIe Gen 4 (up to 16 lanes with a second clock for lanes 16-31), USB 4.0 (up to 40 Gbps), Gen 3, MIPI-CSI 2 for camera integration, SoundWire audio, and upgraded 16 Gbps connectors for Types 6, 10, and 7. These updates targeted AI, , and edge AI workloads, with Type 7 gaining enhanced Ethernet side-band signaling for up to 4× 10 GbE. As of 2025, Revision 3.1 remains the active version, with PICMG's COM Express subcommittee developing Revision 3.2 to incorporate additional peripheral interfaces.

Form Factors

Sizes

COM Express modules are available in four standardized form factors, designed to balance performance, integration density, and physical constraints in embedded systems. These sizes—Mini, Compact, Basic, and Extended—provide for applications ranging from ultra-compact mobile devices to high-end industrial computing. Each form factor specifies precise PCB dimensions and connector configurations to ensure with carrier boards. The Mini form factor measures 84 mm × 55 mm and uses a single 220-pin Golden Finger connector, making it ideal for space-limited environments such as portable medical devices or rugged handhelds. It typically features soldered memory and storage to minimize footprint, with power input ranging from 4.75 V to 20 V. This size prioritizes low power and mobility while supporting essential interfaces like PCIe and USB. In contrast, the Compact form factor is square at 95 mm × 95 mm and employs dual 220-pin connectors (totaling 440 pins), enabling greater I/O expansion. It supports horizontal SO-DIMM sockets with stack heights of 5 mm or 8 mm, suitable for applications needing moderate compute power without excessive board space, such as automation controllers. The Basic form factor, at 125 mm × 95 mm, also uses dual 220-pin connectors and offers additional for enhanced and peripheral integration compared to the Compact size. It accommodates horizontal SO-DIMMs and is commonly used in embedded systems like or transportation controls, where a balance of size and capability is required. The largest Extended form factor measures 155 mm × 110 mm with dual 220-pin connectors, supporting up to two full-size or mini DIMMs, or SO-DIMMs, for high-performance processors and extensive . This size targets demanding applications in or graphics-intensive environments but is less prevalent in modern designs due to the rise of smaller, more efficient alternatives.
Form FactorDimensions (mm)ConnectorsKey Features
Mini84 × 55Single 220-pinSoldered memory/SSD, low power for mobile use
Compact95 × 95Dual 220-pinHorizontal SO-DIMM support, moderate I/O
Basic125 × 95Dual 220-pinEnhanced integration space, mid-range applications
Extended155 × 110Dual 220-pinDual DIMM support, high-performance focus

Types

COM Express modules are categorized by pinout types, which define the specific arrangement and availability of interfaces on the module's edge connectors. These types enable customization for diverse applications by balancing features like support, storage, networking, and expansion capabilities while maintaining standardized mechanical footprints. The specification, governed by PICMG, has evolved to focus on three primary active types in Revision 3.1: Type 6, Type 7, and , with earlier Types 1 through 5 deprecated as of Revision 3.0 to streamline development and reduce redundancy. Revision 3.1 introduces enhancements for these types, including support for PCIe Gen 4 (up to 16 GT/s per lane) across all, USB 4.0 (Type 6 only), optional MIPI-CSI 2 camera interfaces and SoundWire for audio (Types 6 and 10), along with an updated 16 Gbps connector for higher signaling rates, while ensuring with prior carrier boards. The following table summarizes the key interface allocations for the active types, based on the base configurations in Revision 3.0 with noted updates in 3.1:
TypeConnectorsPCIe Lanes (Gen 4 in Rev 3.1)SATA PortsEthernetUSB PortsDisplay InterfacesPrimary Focus
6Dual (440 pins)Up to 24Up to 4 (Gen 3)1x 1 GbE8x USB 2.0 / 4x USB 3.2 Gen 2 (USB 4.0 in Rev 3.1)1x VGA, 2x LVDS, 3x DDI (eDP/HDMI/DP)General-purpose embedded systems with graphics and I/O
7Dual (440 pins)Up to 322 (Gen 3)1x 1 GbE + 4x 10 GbE (KR with NC-SI)4x USB 2.0 / 4x USB 3.2 Gen 2NoneHigh-bandwidth networking and compute-intensive applications
10Single (220 pins)Up to 42 (Gen 3)1x 1 GbE8x USB 2.0 / 2x USB 3.2 Gen 21x LVDS/eDP, 1x DDICompact, low-power systems with basic graphics
Type 6 modules use dual 220-pin connectors (A-B and C-D rows) to provide a versatile pinout suitable for broad embedded applications, including industrial automation, , and test equipment. They support up to 24 PCIe lanes for expansion, four ports for storage, and comprehensive display options like VGA, dual-channel LVDS, and three Digital Display Interfaces (DDI) for resolutions up to 4K via eDP, HDMI, or . Additional interfaces include HD Audio, LPC/eSPI bus, SPI, two serial ports (with optional CAN), eight general-purpose I/O pins, and IEEE 1588 precision timing. In Revision 3.1, enhancements like PCIe Gen 4 and USB 4.0 enable higher throughput for AIoT and , while optional MIPI-CSI replaces some legacy camera support and SoundWire modernizes audio handling. This type is available in Compact and Basic sizes, targeting systems requiring integrated graphics from processors like or . Type 7 modules, also employing dual connectors, prioritize networking and by reallocating pins away from graphics and audio toward expansion and connectivity. They offer up to 32 PCIe lanes (including 16 from the PEG interface), two ports, four 10 GbE interfaces (using 10GBASE-KR with management), and reduced USB to four ports, alongside LPC/eSPI, SPI, serial ports, GPIO, and IEEE 1588. Lacking dedicated display pins, this type suits server-like edge nodes, telecom equipment, and defense systems where raw bandwidth is critical. Revision 3.1 updates include PCIe Gen 4 for faster peripherals and USB 3.2 Gen 2, with full to Revision 3.0 carrier boards. Type 7 is suited for Basic and Extended sizes, often paired with server-grade processors. Type 10 modules feature a single 220-pin connector (A-B rows only), making them ideal for space-constrained, low-power designs such as rugged mobile devices or mini systems. They provide four PCIe lanes, two ports, eight USB 2.0 ports (with two USB 3.2 Gen 2), one LVDS/eDP channel, one DDI for display, plus HD Audio, LPC/eSPI, SPI, serial ports, GPIO, and 1 GbE. This configuration supports basic graphics without the full I/O expanse of Type 6, emphasizing compactness over density. Revision 3.1 adds PCIe Gen 4, optional MIPI-CSI, and SoundWire options, maintaining with Revision 3.0 hardware. Exclusively for the size (84 mm x 55 mm), Type 10 accommodates wide input voltage (4.75-20 V) for battery-powered applications. Legacy Types 1-5, defined in earlier revisions, offered variations like single-connector setups with limited PCIe (e.g., Type 1 with six lanes) or graphics-focused pinouts (e.g., Type 2 with 22 lanes and SDVO), but were phased out to consolidate on modern serial interfaces and reduce carrier board complexity.

Specifications

Pinouts and Interfaces

The COM Express specification employs a standardized connector system to interface the module with a carrier board, featuring up to two 220-pin gold-finger connectors (A-B and C-D rows) for larger form factors, providing a total of 440 pins, while the form factor uses a single 220-pin connector. Rev 3.1 specifies updated connectors rated for 16 Gbps signaling to accommodate higher-speed interfaces. These connectors support differential signaling for high-speed interfaces and single-ended signals for legacy I/O, with pin assignments designed to minimize and ensure reliable data transmission at speeds up to 16 Gbps per lane in Revision 3.1. The pinout is divided into functional groups, including power rails (+5V standby, +3.3V, +12V main, and RTC), ground planes, and signal categories such as PCIe, USB, display, and serial buses, with dedicated pins for module-type detection (TYPE[0:2]#) to allow carrier boards to auto-configure for compatibility. To address diverse application requirements, the specification defines multiple pinout types, each reassigning pins to prioritize certain interfaces while maintaining where possible. Type 2 and Type 3 are legacy-oriented, supporting PCI buses and alongside PCIe, but have largely been superseded. Type 6 focuses on and multimedia, allocating pins for multiple display outputs, /4.0, and a dedicated PCIe (PEG) port. Type 7 is optimized for high-performance, headless computing, dedicating pins to up to 32 PCIe lanes and multiple 10 GbE ports. Type 10 targets low-power Mini modules with integrated support. Revision 3.1 introduces enhancements like USB 4.0 and PCIe Gen 4 support across types, with updated connector options for higher bandwidth. Rev 3.1 introduces optional MIPI-CSI for camera interfaces (via extra 22-pin connector) and SoundWire as an alternative to HDA for audio/sensor applications.
Pinout TypeForm Factors SupportedKey Pin Reallocations and FocusPCIe LanesUSB PortsDisplay InterfacesOther Notable Interfaces
Type 6Compact, Basic, ExtendedGraphics/multimedia emphasis; pins for 3x DDI, dedicated PEGUp to 24 (Gen 4 in Rev 3.1)8x USB 2.0 + 4x (USB 4.0 in Rev 3.1)3x DDI (/TMDS), 2x LVDS/eDP, 1x VGA4x , HDA audio (or SoundWire), 1x GbE, SDIO, 8x GPIO
Type 7Basic, ExtendedHeadless server/high-compute; pins for Ethernet and PCIeUp to 32 (Gen 4 in Rev 3.1)4x USB 2.0 + 4x (USB 4.0 in Rev 3.1)None2x , 4x 10 GbE + 1x GbE, management, 8x GPIO
Type 10MiniLow-power with graphics; single connector limits expansionUp to 4 (Gen 4 in Rev 3.1)8x USB 2.0 + 2x (USB 4.0 in Rev 3.1)1x DDI, 1x LVDS/eDP2x , HDA audio (or SoundWire), 1x GbE, 8x GPIO
The interfaces exposed via these pinouts enable flexible system integration, with PCIe serving as the primary high-speed backbone for peripherals and networking—up to 32 lanes configurable as x16, x8, or x4 links, compliant with Base Specification Revision 4.0 in newer implementations. USB interfaces provide up to 12 ports total, combining USB 2.0 for legacy devices and USB 3.2/4.0 for high-bandwidth applications like cameras and storage, with pins supporting SuperSpeed differential pairs. Display capabilities in graphics-enabled types include Digital Display Interfaces (DDI) for multi-monitor setups via or , alongside embedded DisplayPort (eDP) and (LVDS) for panel-direct connections, while Type 7 omits these for compute density. Storage and serial interfaces are robustly supported, with up to four ports (Gen 3 speeds) on pins shared with PCIe for AHCI or NVMe flexibility, and optional SDIO for card-based expansion. Audio is handled via High Definition Audio (HDA) links on 12 pins for Type 6 and 10, though absent in Type 7; alternatives like SoundWire are added in Revision 3.1 for efficient integration. Management and control pins include /SMBus for system monitoring, SPI/LPC/eSPI buses for flashing and legacy peripherals, two UART pairs (with optional CAN on one), and eight general-purpose I/O pins for custom signaling. Ethernet support ranges from 1 GbE (all types) to four 10 GbE ports in Type 7, with for remote management, ensuring COM Express modules suit both and industrial control environments. Power sequencing and thermal pins, such as SDP (System Design Pins) for clocking and reset coordination, further enhance reliability.

Electrical Characteristics

The COM Express specification defines electrical characteristics centered around a primary of +12 V DC, delivered through dedicated VCC pins on the module's connectors to support the processor, , and peripherals. This voltage rail must maintain a tolerance of ±5% (11.4 V to 12.6 V) under load, with a maximum ripple of 100 mV peak-to-peak across 0-20 MHz to ensure stable operation and compliance with standards. is provided via a +5 V SB (standby) rail at ±5% tolerance (4.75 V to 5.25 V), enabling low-power states and wake events, while an optional +3.3 V auxiliary rail supports (RTC) functionality and is sourced from a lithium battery or the carrier board. Power distribution varies by pin-out type and module size, with Type 6 and 7 modules featuring 24 VCC_12V pins for up to 137 maximum input power, Type 10 modules limited to 12 VCC_12V pins and 68 , and modules supporting a wider input range of 4.75 V to 20 V optimized for 5 V systems. Current draw on the +12 V rail can reach 11.4 A for high-performance configurations, necessitating robust carrier board power delivery networks with low-impedance traces and decoupling capacitors to minimize voltage droop. Power management signals such as PWR_OK (asserted high when voltages are stable), SUS_S3#/S4#/S5# for sleep states, and SYS_RESET# (3.3 V levels) facilitate ACPI-compliant power sequencing. High-speed interfaces adhere to standardized electrical parameters for signal integrity. For PCI Express lanes (up to Gen 4 in Rev 3.1), differential signaling uses 100 Ω ±20% impedance with AC-coupled transmitters, ensuring eye diagram compliance for data rates up to 16 GT/s. USB 2.0/3.0 ports operate at 3.3 V signaling levels, with V_IL max of 0.8 V and V_IH min of 2.0 V for full-speed/half-speed modes, and differential impedance of 90 Ω ±20% for USB 3.0 SuperSpeed pairs. Display interfaces like LVDS employ 100 Ω ±15% differential pairs with V_OD of 350 mV typical, while SATA/SAS links follow 100 Ω differential impedance and 0.6-1.2 V swing for reliable 6 Gb/s operation.
InterfaceKey Electrical ParametersTypical Values
Differential impedance, coupling100 Ω ±20%, AC-coupled
USB 2.0/3.0Input levels, impedanceV_IL: -0.8 V max, V_IH: 2.0 V min; 90 Ω ±20% (USB 3.0)
LVDSOutput differential voltage, impedanceV_OD: 350 mV; 100 Ω ±15%
Swing, impedance0.6-1.2 V; 100 Ω differential
Levels (3.3 V), impedanceV_IL: 0-0.9 V, V_IH: 1.7-3.6 V; 100 Ω differential
These specifications ensure interoperability across carrier boards, with ESD protection recommended at 1 kV for exposed I/O to safeguard against transients.

Mechanical and Thermal Design

The mechanical design of COM Express modules is standardized to ensure compatibility with carrier boards across various applications, defining four distinct form factors to balance performance, space, and integration needs. These include the Mini module at 84 mm × 55 mm, Compact at 95 mm × 95 mm, Basic at 125 mm × 95 mm, and Extended at 155 mm × 110 mm, all with a uniform PCB thickness of 2 mm to facilitate consistent stacking and assembly. The modules employ gold-finger edge connectors with a 0.5 mm pitch: a single 220-pin connector for the Mini size and Type 10 modules, or dual 220-pin connectors forming a 440-pin interface for Compact, Basic, and Extended sizes in Types 1 through 7, enabling high-density signal and power routing without cables. Mounting is achieved via standardized holes positioned to align across all sizes, allowing secure attachment to carrier boards using M2.5 screws and standoffs, with options for top-side (non-threaded) or bottom-side (threaded) fixation at a torque of 0.5 Nm to prevent damage while ensuring mechanical stability.
Module SizeDimensions (mm)Connector ConfigurationTypical Applications
84 × 55Single 220-pinSpace-constrained embedded systems
Compact95 × 95Dual 220-pin (440-pin total)Balanced I/O and needs
Basic125 × 95Dual 220-pin (440-pin total)Standard industrial
Extended155 × 110Dual 220-pin (440-pin total)High-performance with expanded
This table illustrates the form factor progression, where larger sizes support more components like additional slots while maintaining pin compatibility for seamless upgrades. Carrier board design must incorporate matching receptacle connectors (e.g., from vendors like or ) with stack heights of 5 mm or 8 mm from the module underside to the carrier top, resulting in overall assembly heights of 18 mm or 21 mm, respectively, to accommodate heat management components. Thermal design in COM Express emphasizes efficient heat dissipation from high-performance processors and peripherals, mandating a heatspreader as the primary interface between the module and external cooling solutions. The heatspreader, typically a 3 mm thick aluminum plate, is thermally coupled to the module's CPU and other heat-generating components via a gap filler material, serving not as a standalone heatsink but as a uniform surface for conduction to carrier-level or system-wide cooling. Specifications define precise dimensions for the heatspreader across sizes—for instance, the Extended module's version measures 155 × 110 mm with mounting holes offset from the module's to avoid interference—ensuring attachment via implementation-specific spacers or screws without compromising electrical . Cooling strategies are flexible yet standardized, supporting passive and active methods to handle power budgets up to 137 , with thermal monitoring signals like THRMTRIP# (for critical overheating shutdown to S5 state) and THRM# (for over-temperature alerts) integrated into the connector pinout to enable proactive management. Fan control is facilitated by dedicated pins such as FAN_PWMOUT for speed adjustment and FAN_TACHIN for feedback, typically connected to 4-wire fans powered by reclaimed 12 V pins, while advanced options include heat pipes, chassis-integrated dissipation, or liquid cooling for demanding environments. For graphics-intensive modules (e.g., those with MXM slots), additional provisions like TH_OVERT# ensure shutdown within 500 ms of overtemperature detection, underscoring the design's focus on reliability in industrial and rugged deployments.

Applications

Industrial and Embedded Systems

COM Express has become a cornerstone in industrial and embedded systems, enabling modular, solutions for demanding environments. Defined by the PCI Industrial Computer Manufacturers Group (PICMG), the standard supports applications such as industrial automation, , , and control systems, where reliability and scalability are paramount. Its mezzanine-based architecture allows compute modules to plug into customizable carrier boards, facilitating and deployment in space-constrained or rugged settings. In industrial automation, COM Express modules excel due to their support for real-time communication protocols like (TSN) and Time-Coordinated Computing (TCC), which ensure deterministic performance for tasks such as programmable logic controllers (PLCs) and human-machine interfaces (HMIs). Modules often feature extensive I/O options, including MIPI-CSI for camera integration in vision systems and high-speed Ethernet for GigE Vision, enabling efficient at the edge. Ruggedized variants operate in extended temperature ranges (-40°C to +85°C) and withstand high shock and vibration, making them suitable for harsh industrial conditions like floors or transportation equipment. For instance, Advantech's COM Express implementations are designed for robust machinery and high-end systems in automation, providing flexible I/O for mission-critical reliability. A key advantage in embedded systems is the ability to consolidate workloads, reducing hardware complexity and (TCO). Congatec's COM Express modules, for example, have enabled companies like Ono Sokki to streamline systems from seven separate units to a single integrated design. These modules support AI capabilities up to 99 for enhanced efficiency in industrial testing. This modularity also supports future-proofing, as processors and interfaces (e.g., PCIe Gen 4, USB 4.0) can be upgraded without redesigning the carrier board, accelerating time-to-market in embedded projects. Overall, COM Express's standardized pinouts promote across vendors, fostering widespread adoption in sectors requiring long-term stability and .

Other Sectors

COM Express modules find application in the medical sector for tasks requiring high reliability and processing, such as in MRI machines, systems, and surgical . These modules support customizable carrier boards that accelerate AI-driven workflows, including automated measurements in , while adhering to stringent safety standards essential for patient care. For instance, implementations with 11th-generation processors deliver up to 70% graphics performance gains, facilitating high-resolution displays up to 8K for diagnostic visualization. In and defense, COM Express provides rugged, modular solutions optimized for harsh environments, including shock, vibration, and extreme temperatures. Type 6 and Type 7 modules integrate with MIL-STD power supplies and carrier cards to support mission-critical systems in unmanned aerial vehicles and naval , enabling scalable performance without frequent redesigns. The architecture's fanless operation and low-power processors enhance reliability in space-constrained, high-stakes operations like and . Transportation applications leverage COM Express for robust , , and diagnostic systems in railways, subways, automobiles, and . Modules with or Core processors handle real-time data for safety features, tracking, and passenger entertainment, benefiting from the standard's long lifecycle and vibration-resistant design to ensure operational continuity in mobile settings. In automotive contexts, they optimize size, weight, power, and cost (SWaP-C) for autonomous . Within gaming and multimedia, COM Express Type 6 pinouts emphasize multiple display outputs and PCIe lanes to drive graphics-intensive applications like arcade machines, lottery terminals, and high-end gaming centers. These configurations support video streaming and point-of-information kiosks with scalable processing from Celeron to Core i7, providing flexibility for immersive user experiences without excessive power draw.

References

  1. https://www.picmg.org/openstandards/com-express/
  2. https://www.nexcom.com/Support/ComputerOnModule/com-technology/com-express
  3. https://www2.advantech.com/embcore/promotions/COM_2.0/images/com_express_specification_2.0.pdf
  4. https://www.kontron.com/downloads/white_papers/whitepaper_com-express-com-0-rev--2-0_en.pdf?product=88621
  5. https://www.adlinktech.com/eDM/201306_COM_seminar_tks/JP/Next_Generation_COM_Express.pdf
  6. https://www.congatec.com/fileadmin/user_upload/Images/Others/type6_ref_design/congatec_COM_Express_Type_6_Whitepaper.pdf
  7. https://www.scribd.com/document/827102083/PICMG-COM-0R3-0
  8. https://www.picmg.org/resources/news/member-press-releases/congatec-welcomes-official-release-of-the-com-express-3-0-specification/
  9. https://www.eenewseurope.com/en/picmg-com-express-3-1-specification-adds-high-speed-interfaces/
  10. https://picture.iczhiku.com/resource/eetop/WHKEsekhEKzWkBmC.pdf
  11. https://www.congatec.com/fileadmin/user_upload/Documents/Manual/BM45.pdf
  12. https://www.congatec.com/us/technologies/com-express/
  13. https://atlantis.com.ua/media2/uploads/2020/10/22/PICMG_COM_0_R3_0-SHORT_FORM_SPEC_2018.PDF
  14. https://www.picmg.org/picmg-ratifies-com-hpc-fusa-extensions-com-express-pcie-4-usb-4-updates-to-meet-edge-workload-demands/
  15. https://www.prweb.com/releases/picmg_releases_its_newest_com_0_r3_1_spec_for_com_express_to_include_pcie_gen_4_and_usb_4_0_support/prweb18930021.htm
  16. https://www.eenewseurope.com/en/com-express-adds-high-speed-serial-support-for-usb4-pcie4-0/
  17. https://downloadt.advantech.com.cn/ProductFile/Downloadfile4/1-Y9VOBB/SOM_Express_DESIGN_GUIDE_Ed2.1-FINAL.pdf
  18. https://www.fastwel.com/upload/uf/629/PICMG_COMDG_2.0-RELEASED-2013-12-061.pdf
  19. https://www.congatec.com/us/industries/industrial-automation/
  20. https://www.advantech.com/en-us/solutions/embedded-modules-and-design-in-services
  21. https://www.mpo-mag.com/exclusives/medical-computing-com-express-processes-real-time-data-at-the-edge/
  22. https://embeddedcomputing.com/application/healthcare/medical-imaging/leveraging-com-express-for-medical-equipment-design
  23. https://www.elma.com/en/capabilities/com-express
  24. https://www.bcmcom.com/Computer_on_Module_Technology.html
  25. https://www.unmannedsystemstechnology.com/feature/benefits-of-a-com-express-custom-carrier-board-solution/
  26. https://www.adlinktech.com/en/computer_on_modules_com_express_type6
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