Page 285 - Embedded Microprocessor Systems Real World Design

Figure 10.2
STD Board Outline.

An STD bus system consists of a passive backplane with (typically) 4 to 20 slots,
a plug-in CPU, and peripheral boards. The STD bus originally was used mostly with
proprietary (non-PC) CPU designs. As the PC architecture became more attractive,
STD bus boards and systems became available with the same architecture as a PC
and the ability to run DOS or Windows. The number and type of peripheral boards
(timers, 1/0 controllers, standard interfaces, data conversion, etc.) available for the
STD bus is about the same as for the PC/104 bus.
Figure 10.2 shows the outline of the STD bus boards, which are about
4% x 6% inches in size.
There is a newer version of the STD bus, STD-32, which supports 8-, 16, and
32-bit transfers and a 32-bit address space. STD-32 uses interleaved connectors, and
a STD-32 backplane will support older STD cards, allowing a mix of 8- and 32-bit
cards in a system.

VME Bus
The VME bus was based on the Motorola 68000 signals. Using 96-pin DIN (a
European standard) connectors, the backplane may be one to three connectors
wide and up to 20 or so slots long. The VME bus supports daisy-chained interrupts.
It normally is associated with larger and costlier systems.
VME boards come in two sizes: 3U and 6U. Both are approximately 6.3 inches
(160 mm) deep, although there is a longer version used by some systems. 3U boards
have a single 96-pin VME connector and are about 3.9 inches (100mm) wide. 6U
boards have two connectors and are about 9.2 inches (233 mm) wide. A three-panel-
wide 9U board is used in some systems; the third connector is user defined.

266 Embedded Microprocessor Systems