DEALING THE CARDS
The first SBC to implement the
StackableUSB architecture is Micro/Sys' SBC1685. The board
can handle Pentium and Celeron processors with up to 256
Mbytes of SDRAM. It supports PCI-104 (not PC/104) expansion
that's compatible with StackableUSB. Also, it features a Gigabit
Ethernet port, four additional USB ports (plus the four StackableUSB ports), two serial ports, PS/2 keyboard/mouse, a parallel port, an IDE controller, and a CompactFlash interface.
Onboard video handles resolutions up to 1600 by 1200.
Micro/Sys is starting out with the USB148 digital I/O card (). With 53 digital I/O lines along with timers, this board is comparable to other PC/104 boards in
the Micro/Sys product line. The big difference is that it incorporates a 48 MIPS
Silicon Labs 8051 microcontroller (with
built-in USB support), which serves up its
own set of features.
First, microcontrollers of this type
often have other interfaces on them. In
this case, Micro/Sys brings out the 10bit analog-to-digital converter (ADC), dual
UARTs, and serial peripheral interfaces
(SPIs). It also ties the microcontroller's
I2C to the stackable interface.
Second, the Fast USB interface can
handle 12 Mbits/s. This is compatible
with the 480-Mbit/s High Speed USB
interface on the SBC. However, these
two can coexist without any problems
anyway.
Finally, the USB interface is brought
out, enabling this single board to be
used in one of three different environments: the stack; plugged into an external USB port; or as a standalone device using only the onboard microcontroller,
which is possible since Micro/Sys provides access to the 8051.
This approach will significantly
change the way systems can be delivered and designed. That's because the
same hardware can be placed in different locations without worrying about
the software interface characteristics.
Given wireless USB support, a device
may not even be connected directly to
the SBC stack.
It will be interesting to see how the
standard progresses this year and how
it will coexist with EPIC Express. Initially,
the StackableUSB boards will be full
size, but it's possible to implement
smaller cards that would be placed at
the top of the stack (). The size
and layout of the smaller cards have yet
to be fixed.
In theory, two of these cards could fit
into the same space as a full-size card. It
would be up to vendors to create SBCs or
hub adapter cards that would handle
these smaller cards. A complete stack,
including an SBC, could potentially be
built using the smaller form factor. It
would not be unreasonable to contemplate a 1/4-size card given the level of
integration these days.
The StackableUSB architecture complements EPIC Express, the stackable
PCI Express standard. Connectors for
each architecture are on opposite ends
of the card, so it's possible for cards to
support both standards. It's certainly
possible to build SBCs that support
both.
Micro/Sys
www.embeddedsys.com