Purpose
The PC/104-Plus specification establishes a standard for the
use of a high speed PCI bus in embedded applications. Incorporating
the PCI bus within the industry proven PC/104 form-factor brings many
advantages to its users, including fast data transfer over a PCI bus,
low cost due to PC/104’s unique self-stacking bus, and high reliability
due to PC/104’s inherent ruggedness. |
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A Proposed Extension To IEEE-P996
A PCI-enhanced version of PC/104 was developed and offered to the
PC/104 Consortium in September 1996. The Consortium formed a working
group to review and finalize the specification, and PC/104-Plus
was subsequently approved by the Consortium’s voting members in February
1997. |
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The main objective in defining an addition of PCI to PC/104 was
to preserve the attributes that have made PC/104 so successful in
embedded applications, namely:
- Compact .........................................3.6 by 3.8
inches (90 x 96 mm) module size.
- Self-stacking ..................................expands without
backplanes or card cages.
- Pin-and-socket bus connector....reliable in harsh environments.
- Four-corner mounting holes .......resistance to shock and vibration.
- Low power consumption .............low power consumption and
low heat generation.
- Fully PC compatible .....................reduced development
costs and fast time-to-market.
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In addition, it was important that the new embedded form of PCI
also be . . .
- Stackable and usable along with standard PC/104 modules (in
the same stack)
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This added requirement enables newly designed PC/104-Plus modules
to be used in conjunction with the wide variety of preexisting PC/104
"legacy" modules.
Since the 104 pins of the standard PC/104 bus connectors are fully
occupied with the signals of the "ISA" (PC/AT) bus, a new 120-pin
stackable connector was needed to handle the additional signals of
the 32-bit PCI bus. A 120-pin high-density (2mm) connector that precisely
matches the stacking and other dimensional requirements of PC/104
was developed. A unique connector pin "shroud" was also created, to:
(1) guide the male portion of the PCI connector as it mates with the
female portion of the next connector in the stack; and (2) protect
the PCI connector pins, which are slightly thinner and therefore somewhat
more vulnerable than those of the ISA connector.
The resulting combination of PC/104 with PCI, called "PC/104-Plus,"
meets all the objectives listed above. In addition, extensive simulations
have been used to validate its reliability for both current 33 MHz
PCI bus chipsets and future 66 MHz PCI silicon. |
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Two Ways To Use PC/104 and PC/104-Plus
Modules
The diagram to the right shows the basic mechanical dimensions of
a PC/104-Plus module. The module’s form-factor matches that of PC/104,
so PC/104-Plus can be said to be "PC/104 form-factor compliant".
The new self-stacking 120-pin high-density (2 mm) PCI bus connector
fits between the standard PC/104 mounting holes along the edge opposite
the regular PC/104 (ISA) bus, so it consumes minimal space (approximately
10%).
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Spec Summary
Here is a brief summary of the basic specs of PC/104-Plus
modules:
- Module dimensions ...........................................3.575
x 3.775 in. (same as PC/104).
- Spacing between stacked modules ...............0.6 in. (same
as PC/104).
- Data throughput (max.) ......................................132
Mbytes/sec (26 x PC/104).
- Bus drive current (min.) .....................................3
mA (most signals).
- Bus load current (max.) .....................................700
uA.
- Number of PCI modules per stack (max.)......5 (includes "base"
CPU module).
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| The diagram below illustrates a typical PC/104-Plus stack.
8- and 16-bit PC/104 (ISA) modules can be stacked along with 32-bit
PC/104-Plus (PCI) modules, provided that similar type modules
are adjacent to each other. This results in maximum system expansion
and configuration flexibility. |
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| PC/104-Plus, like PC/104, is essentially a repackaged version
of PCI that is optimized for the unique requirements of embedded systems
— where space is scarce and ruggedness is paramount. Although PC/104-Plus
modules provide connectors for both buses, the "120-pin PCI bus" and
the "104-pin ISA bus," only the PCI bus usually connects to circuitry
on such a module. The ISA bus connectors are only there to pass the
ISA bus on for possible use by the next module in a stack. |
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Current status of the PC/104-Plus standard
PC/104-Plus is following in the footsteps of its predecessor.
Numerous companies have programs based on PC/104-Plus. Products
include high performance single-board computers, full-motion video
interfaces, high speed LANs, communications interfaces (100BaseT,
USB, IEEE-1394, etc.), high performance data acquisition and control
interfaces, and PCI bus adapters and bridges. Download a PDF of the
PC/104-Plus specification.
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Desktop
PCI
|
Passive
Backplane PCI
|
PMC
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CompactPCI
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Small-PCI
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PC/104-Plus
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| Dimensions (in.) |
Long: 12.3
x 3.9
Short: 6.9 x 3.9
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12.3 x 3.9
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5.9 x 2.9
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6.3 x 3.9
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3.4 x 2.1
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3.8 x 3.6
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| Area (sq. in.) |
Long: 48
Short: 24 |
48
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17
|
25
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7
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13
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| Bus Connector |
Edge-Card
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Edge-Card
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Pin & Socket
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Pin & Socket
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Pin & Socket
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Pin & Socket
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| Includes ISA bus |
No
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Yes
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No
|
No
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No
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Yes
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| Installation Plane |
Perpendicular
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Perpendicular
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Parallel
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Perpendicular
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Parallel
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Parallel
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| Expands Without Additional Slots (Self-Stacking) |
No
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No
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No
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No
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No
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Yes
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| Positive retention |
No
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No
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Yes
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Yes
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No
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Yes
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| Standards Body |
PCI-SIG
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PICMG
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IEEE
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PICMG
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PCI-SIG
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PC/104 Consortium
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Primary
Application
Area |
Desktop:
motherboard
expansion
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Industrial:
backplane
expansion
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Industrial: VME mezzanine
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Industrial:
backplane
expansion
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Laptop:
factory
options
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Embedded:
SBC expansion
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Standalone Module
Stacks 
