Re: PCI-X 100MHZ

[Lloyd Bircher <nicad2@yahoo.com>]

--- salvador Delgreco <salvador_delgreco@hotmail.com>
wrote:
> Hi,
> 
> If PCIXCAP is low, the frequency capability is
> 66MHZ.
> If PCIXCAP is high, the frequency capability is
> 133MHZ.

Not Exactly.

Expansion cards do not differentiate 100MHz
capability.  Only 66 and 133MHz capability is
available.  The 100MHz option is only available to
133MHz cards plugged into slots limited to 100MHz by
design constraints. 

Non-PCIX devices connect PCIXCAP to ground
PCIX 133 devices connect PCIXCAP to ground via a .01uF
capacitor
PCIX 66 devices connect PCIXCAP to ground via a 10 K
ohm resistor in parallel with a .01uF capacitor

> 
> What is the encoding for PCI-X 100MHZ?

Further distinction is made by the host PCI bridge. 
The bridge drives an initialization pattern on the bus
to inform the devices of what frequency they will be
operating at.

A PCIX bus with a frequency of 100MHz, will drive the
following pattern on the bus during the rising edge of
RST#.

DEVSEL#   Deasserted
STOP#     Asserted
TRDY#     Deasserted

I hope that helps,

W. Lloyd Bircher

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