I/O choices for MicroTCA

What are the best strategies for quickly adding new I/O modules for faster adoption of MicroTCA in non-telecom markets?

An interesting thing happened on the way to developing a new mezzanine specification for AdvancedTCA: It turned into a systems specification. The Advanced Mezzanine Card (AdvancedMC) specification was created to provide a front-panel insertable mezzanine for AdvancedTCA, but it was soon recognized that with a front-insertable module, one could also build backplane systems from AdvancedMCs. This system architecture is referred to as MicroTCA. In order for the MicroTCA market to grow quickly, additional modules are needed. Mezzanine carriers for common small mezzanine cards are one way to quickly enable a vast library of I/O modules that could be used to build MicroTCA systems for new markets.

MicroTCA has emerged as an architecture used across a variety of industries including industrial, mil-aero, and communications applications. I/O products for this tech-nology are minimal at best with the lack of I/O choices slowing the adoption of MicroTCA.

I/O strategy issues

The initial waves of products in a new architecture are typically focused on processing boards, chassis, and communications-centric I/O. Other types of I/O products for industrial and mil-aero markets tend to lag due to the large number of I/O options and the uniqueness of many systems I/O requirements.

When evaluating I/O choices for an architecture, a system designer needs to be aware of several factors that can influence the selection of I/O modules. Time to market is always a key consideration. Whatever the choice, it must allow timely completion of the design, enable a short time to market, and take advantage of open market windows to gain market share and stay ahead of the competition.

Cost containment is at the top of most lists. Non-Recurring Engineering (NRE) costs during development can be very high, and keeping them low is vital. Reusing technology from previous generations, where possible and practical, is one technique to keep NRE costs low. Hardware and software from a previous generation that can be reapplied to the newest generation saves substantial development costs and even inventory costs.

Development time can be greatly reduced if key hardware and software components are available when they are needed. A strategy that makes this possible can substantially reduce development time and reduce costs. And finally, having multiple suppliers to choose from reduces risk and improves the cost benefit.

One of the most effective ways to battle the delay in getting I/O products to market is through the use of well-established mezzanine modules that can be integrated into the new form factors. A great way of doing this with MicroTCA is with one of the established mezzanine technologies.

PCI Mezzanine Cards

The first and most obvious choice is the perennial PCI Mezzanine Card (PMC). Established as a universal mezzanine card, it has an excellent track record and a large base of suppliers with many I/O product offerings to address almost any possible need. The standard PCI bus interface of PMCs is used with most available embedded processors and chipsets, making it a great choice for almost any system. The PMC community has stayed on top of the latest technologies and has upgraded the PMC form factor to XMC, adding PCI Express bus capability to the specification, which expands choices even further. The high bandwidth of the PCI bus and PCI Express bus make this an exceptionally good choice when more bandwidth is required for managing the I/O. Many radar, sonar, and video applications require high bandwidth I/O on interfaces including: high-speed analog and digital conversion; synchronous serial; Ethernet; CAN; SCSI; Serial ATA; USB; FPGA; and many other high-speed interfaces. PMCs are also available for many typical industrial applications like digital I/O, motion control, fieldbus, and others that do not have high-bandwidth requirements.

There is a long list of PMC suppliers with many products in their catalogs. Many of these same suppliers have been upgrading their designs to the XMC variation as well.


IndustryPacks have a heritage as a mezzanine of choice for embedded systems. They are a proven technology with multiple vendors offering more than 300 products to address the various I/O needs of industrial and mil-aero systems. The modules’ smaller size enhances the ability to mix and match modules for the most optimized I/O payload combinations. IndustryPacks are available in low-cost modules for industrial and control I/O with analog, digital, motion control, asynchronous serial, and many other I/O types.

Especially practical in systems where space is limited, the modules provide a high functional density with commercially available modules. It is possible to place up to three IndustryPacks on an AdvancedMC carrier with as many as 150 I/O lines available on a double AdvancedMC.

Carriers compatible with AdvancedMC-based MicroTCA systems exist for PMC and IndustryPack mezzanine modules. Carriers range from one IndustryPack slot on a single AdvancedMC, for example, the TEWS TAMC100 (Figure 1), to three IndustryPack slots on a double slot AdvancedMC. Carriers that can hold a single PMC are available for double slot AdvancedMCs. The MicroTCA specification allows for all combinations of AdvancedMC module types with its backplane pitch spacing, but mezzanines like PMC and IndustryPack are only appropriate for mid- and full-size modules as shown in Table 1.

Figure 1

Advantages of mezzanines for I/O

Using a mezzanine strategy to manage system I/O requirements has many advantages.

  • System requirements change often during development. Using mezzanines at this stage allows for quick integration and evaluation of the many choices for I/O. Development time is minimized and options can be quickly evaluated.
  • Migration from one architecture to the next can be simplified if the I/O payload can simply be moved to the new architecture. Even if only some of the I/O technology can be reused, significant time-to-market savings can be realized.
  • Once the design is fixed, there are alternate options to moving to high-volume production. At certain unit volume levels, it is cost-effective to continue to use the commercially available mezzanine modules. As unit volumes continue to ramp up, there are licensing and custom integration options available to help reduce overall material and manufacturing costs, for example, (left to right) the TEWS TAMC863 and TAMC900 shown in Figure 2. Even at higher unit volumes, the flexibility of choice provided by the mezzanine architecture can be a big design advantage for more model options and field upgrades.
  • Software support is always a very important consideration. Drivers for IndustryPack modules are readily available for all of the major real-time operating systems and Linux. The PCI bus on PMCs and the PCI Express bus of XMCs assure that drivers also exist for the all of the major real-time operating systems, Linux, and even embedded Windows.
  • IndustryPack and PMC carriers have onboard Intelligent Platform Management Interface (IPMI) support for one-stop integration of carriers into the system. IPMI capability also works with alternate suppliers, making integration easier.

Several programs have evaluated MicroTCA for their next generation of computer control. They have existing VME and CompactPCI based platforms that they have successfully redesigned to MicroTCA architecture platforms. They used a mezzanine strategy and have proven that this migration required little modification to the application. Existing I/O solutions based on IndustryPack and PMC mezzanines were moved to AdvancedMC carriers, and their corresponding driver software was simply reused.

IndustryPack and PMC modules have specific applications that play to the strengths of each technology. Some systems will even mix and match the two technologies to leverage the best that each has to offer. A mezzanine strategy for most types of I/O is an excellent way to design cost-effective systems. Be sure to consider both choices, PMC and IndustryPack, in your next design project.

Uwe Tews founded TEWS Technologies. He is very involved in developing real time applications and industrial I/O solutions.

Peter Zimmermann, Dipl. Ing., Vice President of Engineering, joined TEWS in 1983 as a hardware development engineer.