PCI Questions and Answers for the Visual Workstations

PCI Questions and Answers
for the
Visual Workstations / 320 & 540

General Questions

How many busses are there on the new machines?

Each machine has two internal busses.

Does either the 320 or 540 have any 5V PCI slots?

Yes, the 540 has four 5V PCI slots.

Which slots are on which busses?

For the 320, the 32-bit PCI slot is on one internal bus (bus 0), the two 64-bit slots are on the other internal bus

For the 540, four of the 64-bit slots are one bus (bus 0) and are all 5V slots, while the other two slots are 3.3V slots and are on the other bus.

Are there any other PCI devices on these internal busses?

Yes, in the 320 there's a PIIX4 chip on bus 0. This chip provides the IDE controller, USB controller, ISA

bridge and device management functions. On the second bus, there's an Intel Fast Ethernet controller.

On the 540, it's the same as the 320 with the exception that the second bus has an additional SCSI controller device in addition to the two PCI connectors.

Why refer to the busses as "bus 0" and "the second bus"?

Bus 0 - the one with the PIIX4 device - will always be numbered as bus 0. But if there is a PCI bridge device located on bus 0, then the system will look for any busses and devices connected to that bridge before it looks at anything on "the second bus". Normally, if there are no bridge devices on bus 0, the second bus will be bus 1. But since we can't guarantee that this is the case, it's better to not refer to it this way, and just call it "the second bus", or the "second internal bus".

3.3V and 5V PCI Questions

Will 5V Only PCI cards fit in the slots of the 320?

No, they will not.

Will 5V Only PCI cards fit in 540?

5V Only cards will not fit into the two 3.3V slots, but they will fit into the four 5V slots.

What about "universal" cards?

Yes, these cards are made to operate properly in systems with either a 3.3V connector or a 5V connector.

So what kind of cards will fit in the 320 and 540 slots?

Probably the easiest way to show this is with a table:

**Which PCI card types work where?**
PCI Card Type	320 Slots (3)	540 5V Slots (4)	540 3.3V Slots (2)
5V Only	No	Yes	No
Universal	Yes	Yes	Yes
3.3V Only	Yes	No	Yes

Do 3.3V cards use 5V too?

Yes, they can. They don't have to, but the PCI spec shows 5V power pins on the PCI connector regardless of the type of PCI connector used.

Do 5V cards need 3.3V?

They can, but it depends on the way the board was designed. Some designs (of 5V cards) use 5V logic to interface to the bus, but use 3.3V logic elsewhere on the card.

So, if both kinds of cards can use both voltages, what does the 5V or 3.3V nomenclature mean?

The 3.3V or 5V title means that this is the voltage used by the system for signalling. This voltage only refers to the circuitry that interfaces directly to the PCI bus. A "universal" card is designed so that it can operate in a 5V signalling environment as well as in a 3.3V signalling environment. The PCI spec defines specific pins on the edge connector that are to be used only for the I/O circuitry. In the case of a 5V system these pins will have 5 Volts on them, and in the case of a 3.3V system these pins will have 3.3 Volts on them. The diagram below might help in understanding this.

How can I tell if a card is a 5V, 3.3V or universal card?

Few spec sheets actually tell you, so for the most reliable information, you will have to look at a card, or

a photo of a card. The area of interest is the card edge connector.

Here's what to look for:

Are there many 3.3V or universal cards available?

The majority of cards in the marketplace are still 5V. But the industry is moving towards the 3.3V card type. The transition model uses the "universal" card - which works in either type of card slot.

What can I do if there's a 5V card that I need to use?

There is a solution for connecting 5V cards to the 320 and 540. It involves using a Bit3 PCI-to-PCI Expansion box. This product places a "host adapter" into one of the internal slots, and then connects an external chassis with seven 5 Volt PCI slots via an external cable.

The down side of this arrangement is that all the bandwidth of the cards in the external box must pass through the cable and host adapter. If you just want one card in the external box, then it's likely that there won't be a problem. But putting a number of high-bandwidth cards in an external chassis may cause unexpected problems.

My PCI card won't let the system power up. What's wrong?

We've seen a few PCI cards that have been converted from 5V Only cards to Universal cards. In this process some of the manufacturers didn't cut the connection between the I/O Specific pins and the 5V pins on the PCI card. This causes the card to short the power supply's 5V output to its 3.3V output. Fortunately for us, our power supply folds back the current output to Zero and shuts down preventing any damage to the board or our system. Either contact the board manufacturer yourself or send information to the SGI support organization so that we can contact them.