How to Choose a PCI Serial Card |
One of the reasons Greenleaf Software has been regarded well over the years is that we have a knowledgebase that includes
hardware, software, and serial comm systems. We call it context: It poses the question -- how can you troubleshoot a problem
with one component of a system (e.g. a serial card) unless you understand the environment in which it works. Stated again, it
is difficult in the world where the Web rules and anybody can sell anything they wish with little overhead and hardly any
explanation. In this context, serial cards are an important piece of your communications system, and often the problem lies
not with software, driver, or the pretty pictures or low price advertised on the Web or in a store. Often the problem lies in
the attention to detail given a part where there are applicable standards that the part "bumps up against" and creates a subtle
"bug" that isn't clearly software, isn't clearly hardware, and it requires a bit of finesse to understand and choose hardware
that has a good opportunity to be a part of your system. Greenleaf is definitely not the only company that has a wide ranging
knowledgebase and expertise in the software, hardware, and interrelationships between them--but we've gotten accolades from customers
for having a good bit of this expertise.
The PCI bus specification was designed to take the guesswork out of choosing and installing add-in boards. Unlike the ISA bus,
where each board had to be jumper configured by hand, then incorporated into an existing system at a specific address and IRQ
that did not conflict with anything else installed in that system, the PCI bus was supposed to let the system itself take care
of everything. By developing a strict set of hardware and software parameters, the architects of PCI mapped out a system by which
PCI cards could be allocated resources by the Operating System. This way the OS itself could solve and resolve any addressing
or interrupt conflicts occurring as a result of multiple PCI boards coexisting with each other and with other system
devices--without user intervention. However, a PCI system is only as strong as its weakest link. In order for the system to
consistently function properly, all installed PCI boards must completely adhere to all aspects of the PCI specification, and
in a perfect world they would. But, complete adherence to the exacting PCI specification not only requires extensive engineering
expertise, it also requires the purchase of top-quality components and meticulous board design and manufacturing.
Quatech has been manufacturing communication boards for over 20 years, so we have the expertise to do it right. We are also
committed to providing only top-quality boards and to investing the necessary resources to ensure that every Quatech PCI board
complies with all aspects of the PCI specification as closely as possible. Unfortunately, not all companies have the same high
standards we do. Therefore, users need to remember that just because a board is calling itself "PCI" and fits into a computer's
PCI slot, that does not mean that it correctly implements the PCI specification. While a non-compliant PCI board may seem to work
when it is first installed, it might cause problems when combined with other PCI boards (especially other non-compliant boards),
or when moved to a different motherboard, or when the PCI bus is heavily stressed. Is that really a chance you are willing to
take with your system?
We know that Quatech boards aren't your only choice, but we truly believe that there aren't any better ones. The chart below
details the important PCI specification compliance issues to keep in mind when evaluating PCI boards. The following page highlights
the design elements you should look for in a quality PCI board, and shows you what is missing in a non-compliant one.
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Do you see blank spaces on the edge connector instead of a complete row of
gold-plated pins? |
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Notice the two tight rows of "gold fingers" on the Quatech board. This indicates
that all PCI signals and 3.3V power pins are plated, even those that are unused. The result is better data integrity
because high-speed PCI signals use the power pins for return paths
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Non-compliant example... |
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Notice the loosely spaced goldfingers and the large gaps on the non-compliant board.
This indicates that not all pins are plated, and that data integrity may be compromised. |
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Do you see large "pools" or "grids" of ground signals running all over the board? |
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Notice that there are no grids apparent on the surface of the Quatech board. This is because all Quatech boards have
a four layer board design using separate layers for power, ground and signals thus reducing noise and enhancing signal
integrity. |
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Front of non-compliant board |
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Notice the grids of ground signals on the front of the non-compliant board. This indicates the lack of a separate
ground layer and complicates signal routing. This makes the board more susceptible to noise and can compromise
signal integrity. |
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Back side of non-compliant grounding on board |
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Notice the grids of ground signals on the back of the non-compliant board. This indicates the lack of a separate
ground layer and complicates signal routing. This makes the board more susceptible to noise and can
compromise signal integrity. |
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Do you NOT see a row of tiny capacitors (usually rectangular) just above the edge
connector on the front or back of the board? |
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Capacitors which connect the power signal to a ground are part of the PCI specification and are designed to Filter
out noise. As it is fully PCI compliant, the Quatech board includes these capacitors. The capacitors also promote
signal integrity, as high-speed PCI signals use the power pins for return paths. |
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Board without capacitors: Save pennies, risk faulty operation |
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Notice that the non compliant board is missing the required capacitors. This omission makes it particularly
vulnerable to noise problems and loss of signal integrity in high-speed operations. |
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