FreeLists / si-list / [SI-LIST] PCI 4.3.6.2. System Board Impedance

["Gary Levin" <garyl@xxxxxxxxxxxx>]

Anyone have experience with 50 ohms PCI buses for system boards  ?


Gary



4.3.6.2. System Board Impedance

There is no bare board impedance specification for system boards. The system 
designer

has two primary constraints in which to work:

? The length and signal velocity must allow a full round trip time on the bus 
within the

specified propagation delay of 10 ns. (Refer to Section 4.3.5.)

? The loaded impedance seen at any drive point on the network must be such that 
a PCI

output device (as specified by its V/I curve) can meet input device 
specifications with

a single reflection of the signal. This includes loads presented by add-in 
cards.

Operating frequency may be traded off for additional round trips on the bus to 
build

configurations that might not comply with the two constraints mentioned above. 
This

option is neither recommended nor specifically

Regards,

Gary Levin
MangoDSP
972 2  532 8706  ext. 219
fax: 972 2  532 8705

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