Micro/sys proposes StackableUSB

The PC/104 standard is a favorite of embedded designers because of its low cost, rugged form factor and the wide selection of off-the-shelf products. Based on the now defunct Industry Standard Architecture (ISA) bus, the PC/104 standard has been in a holding pattern of late as proponents suggested a variety of updates to modernize the inter-board communications while retaining the other benefits of this stackable, chassis-less architecture. To this end, Micro/sys, a long-time embedded board vendor recently started a movement to create an entirely new stackable architecture based on the PC/104 form factor. The new architecture uses a more modern communications protocol, The Universal Serial Bus (USB), while retaining the size and stacking advantages of PC/104. To encourage support from a variety of vendors, Micro/sys has already announced a compatible CPU board and a general purpose I/O card.

StackableUSB eliminates the external USB cable with a built-in stackthrough connector similar to the legacy PC/104 ISA concept. Without a hub, StackableUSB supports up to 8 USB peripherals top stacked and/or 8 USB peripherals bottom stacked for a total of 16 total boards. With intermediate hub cards, StackableUSB supports up to 76 USB peripherals in the stack. The standard also extends the power over USB limitation from 500mA to 0.9375A per card to eliminate separate power inputs to many peripherals. Like the desktop, stackableUSB integrates Plug and Play to automatically detect devices in the stack and install the necessary drivers with minimal human interaction. You can download the proposed specification and follow the discussion at the new StackableUSB website.