Page 282 - Embedded Microprocessor Systems Real World Design

Most PC/104 CPU boards provide a significant amount of flash memory,
which usually can be configured as a virtual disk drive. This permits you to load an
application and whatever operating system you use into silicon, with no need for a
hard drive or floppy to get everything going. Many PC/104 CPU boards include
an Ethernet connection, and you often can load the software directly from that. If
your embedded controller is talking to an external PC via Ethernet, you can
store the code in the PC and download it on power up. This makes it easy to send
software changes to the field.
Many manufacturers, such as Ampro, make CPU boards that are larger than
the PC/104 form factor but retain the PC/104 interface connectors. This
approach allows more room for components without giving up PC/104 electrical
compatibility.
One drawback to using a PC/104 CPU is the same as that for using a PC: You
may pay for features you don’t use. This occurs for the same reasons it does on a
PC-standard chipsets. Even if your application does not need VGA display, key-
board, or IDE interface, you probably get them on the PC/104 CPU anyway. You
might be able to design a board without those features for less, but remember that
the PC/104 manufacturer spreads development and production costs over a larger
volume than you can. Some PC/104 manufacturers sell a depopulated version of
their boards. If you are not using a VGA controller, for example, they can leave off
the video memory, making the board less expensive.
The introduction of the USB bus may help alleviate some of the size constraints
on PC/104based systems. Current PC/104 CPU boards typically are covered with
connectors. Implementation of floppy, keyboard, printer, serial, and other inter-
faces takes real estate on the board. Even though these functions are embedded in
complex chipsets, IC real estate still is used, and interconnections must be made.
Connector space is tight enough that some PC/104 CPU boards require a floppy
drive from a notebook computer (which is expensive) because no room is left on
the board for the larger, standard floppy connector.
Although I have yet to see one produced, I can imagine a PC/104 CPU board
that does awaywith the floppy, keyboard, printer, IDE, and maybe serial connectors,
using USB instead. Such a board would be targeted at applications that do not need
those peripherals except during development. During development, a “black box”
could be used to interface the USB to all these standard peripherals. This black
box could even be fairly expensive since it would not affect product cost. During
production, instead of having four to six unused connectors on the board, only the
USB is unused. The board space preserved by this approach could be used for other
interfaces or additional CPU functionality.
The pinout for the PC/104 bus is as shown on the next page.

Industry-Standard Embedded Platfwm 263