Over the last five years, the COM Express* has become a popular standard for modular system design. Now the PCI Industrial Computer Manufacturers Group (PICMG*) has released the second revision of the standard to support new graphics and displays technologies, eliminate older interfaces, and better match the features of today’s processors. The new standard, officially known as PICMG COM.0 R2.0, also introduces a new 95 x 95 mm COM Express compact form factor.
Before looking at the new pin-outs, let’s briefly review the existing pin-outs, which are carried over in the new standard. Pin-out type 1 uses a single A-B connector, which has 220 pins. It supports up to eight USB 2.0 ports, up to four SATA or SAS ports, and up to six PCI Express* Gen1/ Gen2 lanes. It also supports dual 24-bit LVDS, Intel® High Definition Audio, Gigabyte Ethernet, and eight GPIO pins. Pin-out type 2 uses the same A-B connector as type 1, but adds a second C-D connector for a total of 440 pins. The second connector adds support for PCI Express Graphics (PEG), a 32-bit PCI interface, and IDE ports for legacy PATA devices. Figure 1 illustrates the type 1 and type 2 pin-outs.
Figure 1 (click to enlarge). The type 1 pin-out uses the A-B connector shown here, while the type 2 pin-out uses both the A-B connector and the C-D connector. (Source: PICMG)
Pin-out types 3 through 5 offer variations on the type 2 I/O. Specifically, type 3 reassigns the IDE pins to create additional Gigabit Ethernet ports, while type 4 reassigns the PCI pins for use as PCI Express lanes. Type 5 combines the changes in type 3 and type 4, so that the IDE and PCI pins are both reassigned. Figure 3 summarizes the legacy pin-outs.
PCI Express Lanes
Up to 6
Up to 22
Up to 22
Up to 3
Up to 32
Up to 32
Up to 3
Figure 2. Legacy COM Express pin-outs. (Source: COM Express Source)
The new type 6 pin-out in COM.0 Rev. 2 is also a modification of the type 2 pin-out. In this case, the PCI pins are used to support digital display interfaces (DDI) and to bump the number of PCI Express lanes up to 23 lanes. The DDI consists of three ports that can be configured individually as HDMI, DVI, or DisplayPort. DDI port 1 additionally supports SDVO. SDVO was already available in the type 2 pin-out, but it was multiplexed with the PEG port. With new type 6 pin-out, SVDO and PEG use different pins, making it possible to use an external PEG graphics card in conjunction with SVDO for applications with more than four screens. In addition to the graphics interface changes, the IDE interface is now reserved for future technologies such as USB 3.0 and SATA Revision 3.0 (also known as SATA 6 Gbit/s).
The new type 10 is a single-connector pin-out intended for compact modules. As shown in Figure 3, this new pin-out is based on the older type 1 pin-out. The main changes are that the number of SATA ports shrinks from four to two, and the number of PCI Express lanes shrinks from six to four. The pins freed up by these changes are now reserved for alternative purposes such as USB 3.0. These better reflect the I/O in processors for small form factor systems. For example, the Intel® Atom™ processor E6xx series and its I/O hub support two SATA ports and 3 PCI Express lanes. Type 10 also gains a DDI with support for HDMI, DVI, DisplayPort, and SDVO in place of the type 1’s secondary LVDS channel, TV out, and VGA support. This change allows the type 10 pin-out to support dual displays.
Figure 3 (click to enlarge). The type 1 and type 10 pin-outs.
In addition to these changes, COM.0 Rev.2 adds serial ports to both type 10 and type 6. The new standard also adds SPI ports for external boot support to the type 10, type 6, type 2, and type 1 pin-outs. For more details on this and other changes in COM.0 Rev.2, see the Advantech COM.0 Rev.2 overview and the Kontron white paper COM Express* COM.0 Revision 2.0.
Leading vendors like Advantech and Kontron are already bringing out modules that leverage the new pin-outs. For example, Advantech is previewing its SOM-5890, which will support the type 6 pin-out. Features of this module will include:
- COM Express basic form factor (95 x 125 mm)
- Second-generation Intel® Core™ processor (previously known as Sandy Bridge)
- 18/24-bit two-channel LVDS, HDMI, DisplayPort, and VGA
- Dual-channel DDR3-1333 SO-DIMM sockets, up to 16 GB
- PEG, PCIe x1, SATA Revision 3.0, USB 2.0, and Gigabit Ethernet
Another product to use the new standard is the Kontron nanoETXexpress-TT. This module uses the type 10 pin-out and offers features including:
- COM Express* ultra form factor (55 x 84 mm)
- Intel® Atom™ processor E6xx series
- Support for industrial temperature range (-40°C to +85°C)
- Onboard E2 SSD Flash drive up to 8 GB
- Gigabit Ethernet, 6x USB 2.0 and 1x USB Client
- 2 x SATA and 1 x micro SD card slot
I anticipate that many other vendors will bring out COM.0 Rev.2 products in the next few months. I look forward to seeing what innovations these modules bring with them!
Advantech and Kontron are Premier members of the Intel® Embedded Alliance.
Roving Reporter (Intel Contractor)
Intel® Embedded Alliance
Embedded Innovator magazine