Diodes Menu Close
Diodes Pericom: A product line of Diodes Incorporated

Frequently Asked Questions

Search our knowledge base of commonly asked questions to find answers to your questions about Diodes Incorporated's and Pericom's products and services.

Results for STB

Any recommendations for off the shelf utilities to help tune our bridge application?

Yes. Under any Windows OS, one excellent shareware tool is at www.PCItree.de Follow the install directions in the pt_userg.html file. Changes made with this tool are not permanent, so tuning bridge registers is safe and easy.

 

Any special attention needed for the 7300D placed into a very old system?

The BIOS date is important. The bridge counts 225 PCI clocks from the de-assertion of P_RESET# to the first allowable PCI config cycle, per PCI Spec 2.2**. This is 33 million clocks, about 1 full second at 33 MHz. For BIOS made according to Intel/Microsoft AC97 ("green PC") specification, this 1 second (at 33 MHz) delay is not a problem. But for older BIOS standard, this will block BIOS from enumerating the PCI devices on the secondary PCI bus and thus they have no resources assigned. Since DOS uses the BIOS for PCI enumeration (enumerate == "detect and assign resources"), a motherboard BIOS older than 1996 years might not detect and allocate resources to devices behind the bridge. When plug and play OS loads (many seconds later), then its first enumeration of the computer will detect our bridge (and the devices behind it). Thus Windows 9x and Windows ME OS will detect the bridge, as will any motherboard modern enough to run Windows 2000 or XP. **This is found at page 128, section 4.2.3.2 "Timing Parameters" PCI specification 2.2 table 4-6, Trhfa "RST# High to First Configuration Access". A workaround exists: Place two diodes, P_RESET# to S1_REQ#6 And P_RESET# to S1_REQ#7 so that as P_RESET# is low the internal arbiter senses S1_REQ#6 and S1_REQ#7 low. The diode blocks normal REQ# assertion from resetting the system, but allows P_RESET# to pull low the corresponding S1_REQ#.

Are Linux drivers available for the 8150 PCI Bridge?

The bridge uses the generic PCI-PCI bridge driver already part of Linux kernel 2.2; there is no need for a Pericom specific driver.

 

Are Linux drivers available for the PI7C7300D?

The pci-pci bridge will appear to your OS as two standard PCI-PCI bridges. We require no added device driver for Linux kernel 2.2 and higher; our test under Linux (Red Hat 7.0 on Intel PC) locates, configures, and runs devices behind the bridge.

 

 

 

 

Can I float inputs such as the REQ# signals, MSK_IN or S_CFN_L?

No, Inputs should not be left floating. Pull DOWN pin 23 (S_CFN_L) secondary bus arbiter select. Pull DOWN pin 126 MSK_IN to turn on all the secondary bus clocks without programming through GPIO. REQ signals should have pull-Ups to Vio. See Application Notes 55 , 58 , 60 for further details.

 

Can I have the two busses work at different frequencies?

Yes, you can have the secondary bus running at similar speed at the primary, or you can have the secondary bus running at half the speed of the primary bus. So, if the primary bus is running at 66 MHz then the secondary bus can be running at 33 MHz or 66 MHz. This is controlled by Config66 and s_m66en signals. If both are high, then the secondary will run at the same speed as the primary bus. If either one of them is low, then the secondary bus will run at half the speed of the primary bus.

 

Can I plug this board in a PCI-X slot?

Yes you can, the PCI-X specification is backward compatible with this bridge, and it will work at 66 MHz speed.

Can I select 33 MHz operation on the Primary, even with the Primary clock being 66 MHz?

A 66 MHz bus normally drops to 33 MHz when the M66EN signal is driven low. So, you could bring down the primary bus to 33 MHz by tying or pulling low the P_M66EN signal, if that is your wish. More importantly, some other card might do this to you if it is designed for 33 MHz but plugged into a normally 66 MHz bus.

 

Can memory mapped address space for a secondary bus device be larger than 1 MB?

Yes. Address space is reserved in multiples of 1 Mb for the prefetchable and non-prefetchable memory spaces.

 

Can the primary and secondary buses of the 8152 be set to different clock frequencies?

No

 

 

No
Can the secondary bus run at a higher speed than the primary bus?

No, the secondary bus runs at equal or half the frequency of the primary bus.

 

Can this work in a 64-bit slot?

Yes, you can plug it in a 64-bit slot. The system will automatically resize the slot to 32-bit, all transfers will occur at 32-bit data width.

Can unused secondary clock s_clk[1..4] be unconnected or do I need to disable them by programming bridge registers?

Tie one clock to S_CLKIN (pin 51). The other unused clocks can be unconnected.By default all the clocks are enabled; unused clocks can also be turned off at the Secondary Clock Control Register (configuration register offset 68h, bits 8:0).

 

 

Tie one clock to S_CLKIN (pin 51). The other unused clocks can be unconnected.By default all the clocks are enabled; unused clocks can also be turned off at the Secondary Clock Control Register (configuration register offset 68h, bits 8:0).
Can unused secondary clock s_clk[1..9] Be unconnected or do I need to disable them by programming the clock mode (using GPIO and MSK_IN)?

Tie one clock to S_CLKIN (pin 21 for the FQFP 208 pin package). The other unused clocks can be unconnected; connect MSK_IN (pin 126) low to skip using the GPIO clock programming circuit and the unused clock outputs can be left no connect.

 

Do designers make use of a pie filter or does a simple decoupling scheme using say, 0.1uF and 22uF Caps, work sufficiently?

Either could work, so long as the total decoupling capacitance is provided. Our general guideline is to decouple power entering the board with .1 and 10uF caps and again for safety at the four corners of the bridge IC with .1, .01, and 10uF caps.

 

Do I need a hot-swap controller to design Hot -Swap hardware?

Yes, a Hot swap controller is needed to ramp up the power as needed. It will also shut down if there is something wrong and there is too much current flowing through the Vcc planes.

 

Do I need to write a driver in order to use a PCI-PCI bridge?

Our bridge doesn't need a Pericom specific device driver. At the Windows 2000/XP level, the generic pci-pci bridge driver pci.sys is all that is needed, which comes with every windows. Linux (Red Hat 7) supported our bridge with no driver from us, using a default pci-pci bridge driver.

 

 

Our bridge doesn't need a Pericom specific device driver. At the Windows 2000/XP level, the generic pci-pci bridge driver pci.sys is all that is needed, which comes with every windows. Linux (Red Hat 7) supported our bridge with no driver from us, using a default pci-pci bridge driver.
Do Pericom's Packet Switches Support Industrial Temperature Range (-40oC to +85oC)?

"YES, please refer to the following application notes.

AN219 – GreenPacket PCI Express Packet Switch – Industrial Temperature Support 1.0

AN220 – PI7C9X20303SL-404SL Industrial Temperature Support

AN221 – PI7C9X20303ULA Industrial Temperature Support"

 

Do the P_Vio / S_Vio pins control the output voltage or the output driver levels?

P_Vio and S_Vio pins at our bridges control "output driving strength", which is related to current not voltage levels. The V/I curves between 3.3 V signaling and 5V signaling spec differ, and our exact pullup and pulldown curves can be viewed from our IBIS model, where "high drive" is with (P/S)_Vio input of 5V and "low drive" is (P/S)_Vio input of 3.3V.

 

Do we need to configure any of the registers to make this bridge function?

Generally the system BIOS (in non plug and play environment) will configure the bridge -- that is, assign PCI bus number, enumerate (detect and assign address ranges) devices on the secondary buses, and update the memory ranges assigned to each bus. The OS does this for plug and play systems. Once this much configuring is done, the bridge can forward transactions in either direction without further Pericom-specific drivers being needed. For the Windows and Linux environments the bridge uses the generic bridge driver already part of the OS kernel.

 

Do we need to mount a heat sink for 66 MHz applications?

Maybe. You'll want to determine temperature at the die junction, but that involves first knowing the power, the thermal resistance (theta Ja) of the part, and the ambient air temperature. Power = Vcc * Icc. Peak traffic generates the following current at the bridge: Peak ICC @ 3.6V Vcc. 5 MHz 61 mA (all 3 buses at 5 Mhz). 33 MHz 310mA (all 3 buses at 33 MHz). 66 MHz 780 mA (all 3 buses at 66 MHz). Theta Ja for the NA272 package is 27.55 C/W. Tj = Temp_Air + Power[Theta Ja]. See Packaging Mechanicals for more information.

 

Do you have an application note on FET isolation that you recommend?

The best and most recent app note for hot insertion *Switches* is Application Note 52 .

 

Do you have any decoupling recommendation and other schematics and Layout guidelines?

Yes, all these guidelines are available in the Hardware implementation Guides. All relevant Application Note/Briefs are available under the APPLICATION NOTES tab on the PRODUCT DETAIL PAGE for each product in the FINDER tool. Please refer to Bridges

Hardware Implementation Guide for PI7C8150 PCI-PCI Bridge

Hardware Implementation Guide for PI7C8152

Hardware Implementation Guide for PI7C8154.

 

Do you have any decoupling recommendations and any other schematics and layout guidelines for this device 7300D?

Yes, all these guidelines are available in the Schematics and Layout guidelines for the 7300. See Application Note 44.

 

Do you have any decoupling recommendations and other schematics and Layout guidelines?

Yes, all these guidelines are available in the Hardware implementation Guide for the PI7C8154. See Application Note 60

 

Does it support both Non-Transparent Mode and Transparent Mode?

The 7300D and 815x family of bridges are transparent bridges.

 

Does the 8150 have any power ramping requirements?

When first powering the chip, either power the core voltage (3.3V) before powering Vio or allow 3.3V and 5V to rise together (as is normal for motherboard power supplies).

 

Does the 8152 have any power ramping requirements?

When first powering the chip, either power the core voltage (3.3V) before powering Vio or allow 3.3V and 5V to rise together (as is normal for motherboard power supplies).

 

Does the bridge implement cache snooping?

The bridge does not do any cache snooping. The PCI bus is not responsible for snooping. If you think that snooping is required then you have to have your own cache controller on the PCI bus to do snooping. The bridge stores memory writes briefly but they continuously are written to the far side of the bridge. If you wish to flush the posted write buffers, your application should place an IO write or IO read command into the transaction queue. Memory writes initiated after that commands are executed after the IO transaction concludes.

Does the bridge support industrial temperature?

No, This is a commercial level grade part only.

 

Does the internal arbiter rotate between S1 and S2 or are they arbitrated independently? Do both buses need to be idle before a transaction can start?

Each of the three buses {Primary, secondary S1, secondary S2} are independent and thus each will be arbitrated separately, regardless of activity or idle state on another bus.

f I supply 66 MHz to the Primary Clock input, can I choose between 33 MHz or 66 MHz on the Secondary buses?

Yes, depending on the state of signal S_M66EN, when the primary Clock is 66 MHz you can have both, either, or neither secondary bus set to the same speed (S_M66EN = high) or half speed of the primary bus (S_M66EN = low).

 

For the 66 MHz enable signals, do they only affect the chip during startup? Is this pin looked at by the PI7C7300 after initialization?

The M66EN signals are used directly to the control logic. We do not use the M66EN for strapping, (and thus the M66EN signals are "live" at all times).

 

GPIO support for PI7C8154A?

GPIOs exist in the PI7C8154A. Please check Configuration register offset 64H in the data sheet.

 

Hot-Insertion: Is it guaranteed "Safe" to Remove or Insert a module containing the PI7C7300D device from a powered up "live" system?

The PI7C7300D is "hot-swap friendly", which essentially means it can interface to a hot-swap power controller. But by itself cannot withstand Vcc=0V and live signals at the I/O pins -- in this mode, current will flow through our bridge. Therefore, if ever there is a possibility of this happening, we require a hot-swap power controller and switches for isolation. If you do not need to pre-charge your switched signals, then the less costly or PI3C32X245 switches are appropriate for the signal switches. Most of our customers use this switch in their applications.

 

How can I increase performance on this chip?

Normally, most motherboards set the Cache Line Size of the motherboard primary PCI bus (i.e. system North Bridge) to 8, with some of the newer ones choosing 16. At boot time, the system BIOS copies this value to our bridge CLS register. The number is small where little bursting is expected; but smaller burst lengths decrease available PCI bandwidth. The tradeoff is that small bursts have smaller latency, that is, less impact on other devices waiting to use the PCI bus. This said, in general the best possible performance occurs with our bridge set to cache line size “00”, which allows read and write bursting to 4Kb address boundaries and prefetch behavior identical to cache line size 16. The best possible latency happens with smaller CLS values in the range of 4 to 8.

 

How compatible is your part to the 21152? Will Intel drivers work with this device?

The PI7C8152A was intended to be a pin compatible drop-in replacement to the Intel 21152. The drivers that currently work for the Intel device will function with our device as well. The PI7C8152A does not require any external drivers, but instead utilizes the embedded drivers in Windows. The only issue that may come up is that if your software is looking specifically for the Intel device and vendor ID's, it will need to be modified. The PI7C8152A has an added feature, it can work at 66 MHz. our device ID and vendor ID are different from Intel's.

How do we connect the reserved Pins?

RESVD (pin 127 in package MA-208) is at J14, leave this as NC (no connect),RESVD (pin 128 in package MA-208) is at J16, leave this as NC (no connect).

 

How do you set non-prefetchable read mode?

Non-prefetchable read transactions use single DWORD data phases. Section 3.6.3 “Read Prefetch Address Boundaries” shows that Memory Read Line and Memory Read Multiple commands implicitly prefetch. Memory Read commands behave differently: For Downstream memory read commands (i.e. target device is on the secondary PCI bus), program config address 20h with your memory mapped I/O range (i.e. non-prefetch) and for config address 24h the prefetch base address needs to be *higher* than the prefetch limit address. Example: [Config register offset 24] write 0000FFFF (which will read back as 0000FFF0 as the last byte is RO) [Config register offset 28] defaults to 00000000 so the upper 32-bits for prefetch base and prefetch limit line up . Upstream defaults to PREFETCHABLE due to config offset 40h bit 4 = 0 after reset. Write offset 40h bit 4 to be "1" to turn off upstream prefetching.

 

How does the bridge know to forward a transaction to the correct bus? Will PCI traffic on either secondary bus to the other secondary bus of the same bridge IC impact traffic at the primary bus?

At boot up, the BIOS probes each PCI bus to look for PCI devices that have memory or IO requirements. When finished reading all possible device numbers, the PCI Bridge, which owns that PCI bus, has memory ranges programmed for (I/O, non-prefetchable memory, and prefetchable memory). This continues until BIOS has found all PCI buses and all devices on those buses. After that, whenever a PCI transaction happens, the bridge checks the address of the target against the memory RANGE programmed at each bus within the BRIDGE configuration register. If the initiator is on a secondary bus and the target address is outside the ranges (start address until end address) of all the memory and I/O address registers, the transaction is forwarded to the primary PCI bus for some other device to claim it. If the initiator is on the primary PCI bus and the target address does not decode to one of the address ranges in config register 0 (for bus S1) or config register 1 (for bus S2), then the bridge does not claim the transaction. In both cases, the CPU is not used.

 

How large are the posted Write FIFOs on this bridge?

This bridge has two separate posted write FIFOs or buffers, each with 32 DWords (128 bytes) and one per side (i.e. one on the primary PCI port and one on the secondary PCI port). These two FIFOs are used to store all memory write and memory write invalidate transactions going through the bridge. The bridge will continue to store data (until an internal boundary is met) as long as there is room in the FIFO. Once the bridge has one entry, it will start to empty the FIFO on the other side. For the PI7C8154 , there are two posted write buffers of 32 DWords in each direction in order to accommodate the 64-bit data path (thus 256 bytes of data in each direction).

 

How large are the Read FIFOs on this bridge?

This chip has two 128-bytes of delayed transaction buffers, one FIFO on each side. Read transactions are treated as delayed transactions and are stored in this FIFO. When the bridge receives a Memory read request, it will continue to prefetch data until the FIFO is full, or it reaches an internal boundary if this transaction is prefetchable. If this is not prefetchable, like I/O read, configuration read, or a non prefetchable memory read cycle, then the bridge will read the requested read data only. The PI7C8154A is similar except it has two 32 Dword FIFOs in each direction in order to accommodate the 64 bit data path (thus 256 bytes of data in each direction).

 

How long has the 8154 been in production?

The PI7C8154A was released in November 2002.

 

How should I connect pull-ups? To which voltage level?

We recommend using Vio for pull-ups.

 

How to reset the bridge by software?

There are two reset bits:1- secondary reset -- bit 22 offset 3c Hex This bit will reset the secondary interface signals and the FIFOs.2- Chip reset -- bit 8 offset 40 Hex .This bit will reset the entire chip, primary, secondary bus and the FIFOs as well as the internal registers.

Is the FIFO depth adjustable?

No, FIFO depth is a fixed size.

 

Is the primary PCI bus idle/available for use while traffic moves from S1 to S2?

Yes, the primary PCI bus is idle/available for use while traffic moves from S1 to S2.

Is there a way to prevent devices on S1 to communicate with devices on S2?

Traffic originating on a bus that has a target address decoding to the same bus is not propagated to other buses. If the target address decodes to the other secondary bus, the transaction is placed into either the posted write buffer or the delayed transaction buffer of that target bus (depending on the PCI command used) and will commence at the other bus when the bridge next receives grant from the arbiter. If the target address decodes to neither secondary bus, and is initiated from a secondary bus, the bridge forwards it to the primary PCI bus by placing the transaction into the proper FIFO for that PCI command. If the initiator is already upstream from the bridge and the target is also upstream from the bridge, the bridge does not claim the transaction. There are no "protected" or "non-transparent" address spaces; one of the above four conditions applies.

 

Is there any loading issue with 2 bridges at a 66 MHz primary bus?

Each bridge based add-in card loads the primary PCI bus by one Load, regardless of the number of devices placed on the secondary buses of that bridge IC. PCI specification revision 2.2 allows 2 loads at 66 MHz and 4 loads at 33 MHz.

Is there any way to program the internal arbiter such that it does not follow the round robin system?

The internal arbiter has two possible priority levels for each secondary bus master device and the bridge itself. These are programmable at configuration register offset 40h. By selecting some devices as high priority and some as low priority, you can give preference to a high bandwidth or time-critical device.

Is this part 5V tolerant, and what signaling environment does it support?

Yes, This part is 3.3V core, but signaling can be at 3.3V or 5V. Two signals are involved P_VIO and S_VIO, according to what these two signals are driven to. The specific primary or secondary bus will be driving either 3.3V signaling or 5V signaling. The input is also 5V tolerant.

 

To which version of the Intel 21154 is the PI7C8154 pin compatible?

This bridge is designed to Intel 21154BE capabilities (power management support at pin D11, 2KV ESD rating, 0.35 micron process, and more robust tolerances for 3.3V/5V power start up sequence.) The bridge also can be used in designs intended for 21154 versions AC, AE, and BC also.

What do I need to do to modify my driver to take advantage of Pericom's cache line size 0 application performance improvement?

Detect the address of the PCI bridge (since the address will change according to slot on the motherboard and according to the motherboard). Make a PCI type 1 Config Read at the above bus/device/function=0/offset=0C with size of 1 Dword.Use the AND operation: (with the above Dword AND FFFFFF00h).So that bits [0 to 7] are cleared to 0. Use PCI type 1 configuration write to write the new value to bus/device/function=0/offset=0C.That is the entire modification needed.

 

What is a PCI-to-PCI Bridge?

PCI-to-PCI-Bridge is a chip that has a PCI interface on the one side (we call it the primary bus), and it also has another PCI Interface (this is called the secondary bus) on the other side. It is a chip that allows you to add another PCI bus onto your system.

What is the data width and maximum frequency of the 8152?

This is a 32-bit, 66 MHz PCI-to-PCI bridge that adheres to the PCI specification rev 2.2, PCI-to-PCI bridge spec 1.1.

 

 

What is the data width and maximum frequency of the PI7C8150?

This is a 32-bit, 66 MHz PCI-to-PCI bridge that adheres to the PCI specification rev 2.2, PCI-to-PCI bridge spec 1.1.

 

What is the junction temperature of the 8150?

Junction temperature, at peak traffic/peak operating frequency:Tj = Ta +P [Theta Ja]. For the ND (256 pin BGA) part, Theta Ja is 31.2 °C/watt; the MA part uses Theta Ja of 39 °C/watt. Peak traffic/66 MHz on both PCI buses uses 1.39 W power. If we use those numbers in the formula: Tj = 85 °C +1.4w[31.2 °C] ? 125.6 C (256 pin BGA, package ND)Tj = 70 °C + 1.4w[39 °C] ? 124.6 C (208 pin FQFP, package MA) We know the component performs according to all rated specifications until junction temp exceeds at least 125 C.Typical power consumption at 33 MHz primary bus /33 MHz secondary bus is somewhat less than half, around 600mW. See packaging mechanicals for more information.

 

What is the requirement of the reference clock of Pericom's packet switches?

The reference clock DC specifications and AC timing requirements are shown in the table below. More details can be found in "PCI Express Card Electromechanical Specification Revision 1.1", Chap 2.1.3.

 

What is the Vendor and Device ID # for thePI7C8150?

"VendorID = 12D8 h

DeviceID = 8150 h"

 

What is the Vendor and Device ID # for thePI7C8152?

"VendorID = 12D8 h

DeviceID = 8152 h"

 

What is the Vendor and Device ID # for thePI7C8154?

"Vendor ID = 12D8 h

Device ID = 8154 h"

 

What power up sequence is needed for the PI7C7300?

We expect core Vcc (3.3V) to be present before IO is present for hot-swap applications. Hot-swap applications will need a hot-swap controller and external switches to limit induced current through the bridge. For power on ramping, we expect 3.3V and 5V to begin ramping at the same time, so that the delta between them stays around 1.7V or less, on the assumption some devices will have pull-ups to Vio, which might be tied to 5V.

 

What should I do with unused REQ# and GNT# signals?

Pull up the unused REQ# signals; you may use a single resistor in the 5K-8K ohm range tied to Vio to reduce parts count. GNT# is an output from our bridge IC and can be left not connected.

 

What's the difference between Intel and Diodes' FIFO sizes?

(From http://www.intel.com/design/bridge/index.htm ) The Intel 21154 has (in bytes). Primary write = 88 bytes , read = 72 bytes, Delayed entries =3 secondary write= 152 bytes . read =152 bytes, Delayed entries= 3 . For the Diodes' PI7C8154: (posted write buffer and delayed transaction buffer data size for FIFOs) primary write= 128+128 bytes. Read= 128+128 bytes. Delayed entries= 8. The same for the secondary. Thus the Diodes' 8154 has MORE FIFO buffering than Intel.

 

When using the PI7C7300 in hot-swap hardware, which Vcc do I connect it to?

According to the hot-swap specification revision 1.0., the bridge should be connected to early power. All other chips on the board should be connected to switched power, which comes later, driven from the Hot-swap controller.

 

Where are the MS0 & MS1 pins in Pericom PI7C8150 PBGA pci-pci bridge device?

MS1 (pin 106 for package MA-208) is pin R16 for the BGA 8150. It is normally connected to VSS. MS0 (pin 155 for package MA-208) is pin B14 for the BGA 8150. It is normally connected to VDD.

 

Why are MS0 and MS1 signals also listed as VDD and VSS pins?

These are actually multiplexed pins. By default, we are compatible with the Intel 21150 solution, where pin 155 is VDD, and pin 106 is VSS. In future versions of this chip, changing the setting (pulled HIGH or LOW) on these pins will allow for future features. For now, these optional capabilities are reserved.

Why do I need a PCI-to-PCI-Bridge?

There are many uses for this chip including:

1) To alleviate the excessive loading on the motherboard. This chip can be used on a server board, or a main board in a system that needs many I/O cards connected to it; these I/O cards can be Ethernet, Fiberchannel, SCSI, or any other PCI I/O cards. PCI specification rev 2.2 allows you to have as many as 4 slots @ 33 MHz slots and two 66 MHz slots. If your system requires more then 4 slots, then you need to add a PCI-to-PCI Bridge. This bridge will take one load only, but it will allow you to add four additional slots on the other side. See Figure 1 of Application Note 55 available on the web.

2) If you have more than one PCI interface chip on an add-in card. If you are designing an intelligent add-in card that requires a CPU and an I/O chip like Ethernet, SCSI, or Fiberchannel, then you will have two or more PCI loads, in this case you must have a PCI-to-PCI bridge on the card. The PCI specification rev 2.2 allows only one PCI Load connected to the PCI Edge connector. See Figure 3 of Application Note 55 available on the web.

3) If you have many types of interfaces, and you would like to isolate each application’s traffic to a specific bus (example: you have couple of Ethernet chips on your system that need to be 32-bit and 66 MHz and have two low-performance 32-bit applications like modem cards running at 33 MHz). In this case, to isolate the two distinct applications you would add one bridge for the 66 MHz high-speed I/O interfaces, and another bridge for the low-speed applications. The benefit is that the high speed I/O card does not have to wait for the low-speed application to finish its transfer. You will also have one bus running at 66 MHz and another slow bus running at 33 MHz.