Although there are many embedded application that run headless, there are many more that require a visual interface for users. And even if the in-field application doesn’t require a display, developing engineers find having one more than just a little helpful in the lab for troubleshooting.
Plugging in a display is pretty easy during platform evaluation as likely you’re working with a vendor-supplied COM Express module and companion Evaluation carrier board (i.e. the Kontron ETXexpress-PC and the ETXexpress Eval2 carrier board). The evaluation carrier board brings out a wide array of I/O and peripheral connections. The difficult part comes up when you start design and bring up of a custom carrier board.
Best to start by making sure the features supported by the COM Express modules computing core platform (i.e. the Intel® Core™ 2 Duo processor, GM45 and ICH9 chipset) are matched with the needs of your application. If a particular display feature is not supported by the platform, you’ll need to incorporate the appropriate controller into the carrier board. Even if the core platform does have support for the needed display interface, making sure that the system is talking correctly is key.
So, how do we make the core and the carrier talk correctly to the display? It comes down to the routing. For this example we’ll focus on VGA, but know that COM Express does support other display options and specific routing is applicable for each.
The VGA signals for a COM Express design must be routed in the following manner:
- From the COM Express Connector to the 150-Ohm Parallel Termination at the VGA Connector: 55 Ohm
- From the 150-Ohm Parallel Termination to the VGA Connector: 75 Ohm
I’ve said it before and it bears repeating – You’re not alone! Make sure that consulting with your computing core supplier is an integral part of your design process. They have the experience of internal design as well as supporting a diverse range of user-side applications. If yours is a routing issue or something else, your supply partner will be able to help you not only to trouble shoot the issue, but to resolve it or even avoid it in the first place.
Christine Van De Graaf
Product Manager, Embedded Modules Division
FYI – Running into display integration complications? Signal routing issues? Kontron’s application engineering teams located worldwide can help!