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Choosing a Quality PCI Communication Board

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Guide to Choosing a Quality PCI Communication Board


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.

Compliance Issue Importance Quatech Boards other manufacturers
All unused 5V and 3.3V power pins are plated on the connector (goldfingers) Better data integrity because high-speed PCI signals use the power pins for return paths YES! sometimes, often omitted when "cutting corners"
All 3.3V power pins are decoupled from ground with capacitors Better data integrity because high-speed PCI signals use the power pins for return paths YES! rare, ground return path capacitors are often omitted
All PCI signal lines have one and only one load. (connected to only one pin on one component on the board) Better data integrity because the PCI bus is extremely sensitive to signal loading YES! usually, but sometimes violated
JTAG boundary scan chain intact if unused (connect TDI to TDO signals) JTAG boundary scan systems can work with the board installed YES! extremely rare
Trace length of 1.5" or less on PCI signals PCI signals rely on specific travel times up and down the bus. Proper trace lengths ensure data integrity YES! usually, but sometimes violated
PCI clock trace is 2.5" 0.1" in length The PCI clock signal timing is particularly critical. All other PCI signals depend on accurate clock delivery YES! often violated
Full PCI configuration space implemented So that plug-and-play really works YES! almost always, but there are some exceptions

 

Look closely at the PCI card you are considering buying. Does it comply with all aspects of the PCI specification? Quatech boards do. Can you really afford the potential aggravation of using a non-compliant board in your system?

 

 

Do you see blank spaces on the edge connector instead of a complete row of gold-plated pins?
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.

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.

Do you see large "pools" or "grids" of ground signals running all over the board?
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.

Notice the grids of ground signals on the front and 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.

Front of board


Back of board

Is your board truly Plug & Play? Or, do you see jumpers for setting basic configuration parameters such as address?
The Quatech board contains a controller chip in which all PCI configuration registers are properly implemented. This means that the PCI BIOS can use the information stored on the chip to automatically configure the Quatech board, making it truly Plug & Play.

The non-compliant board has no controller chip, and basic configuration settings such as address and IRQ must be selected manually via jumpers on the board. Not only is this board not Plug & Play, it has the potential to conflict with other PCI devices in the system.

Do you NOT see a row of tiny capacitors (usually rectangular) just above the edge connector on the front or back of the board?
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.

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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