User manual

Kontron Compact Computers AG SMX945 Detailed Manual V1.1
48
The PCI Local Bus Specification requires that:
 PCI clocks be synchronous within a 2 ns window at the destination devices
 the maximum propagation delay for the clock be 10 ns
 PCI slot-based add-on cards implement a PCI clock trace length of 2.5 inches
T
MD
Propagation delay: module PCI clock source to on-module PCI device
T
MC
Propagation delay: module PCI clock source to module connector PCI clock pin
T
CD
Propagation delay: module connector to carrier board device
Fixed by COM Express
TM
Specification at 1.6 ns
T
CS
Propagation delay: module connector to slot connector pin
P
SD
Inverse propagation speed: slot card connector pin to slot card device
T
MD
= T
MC
+ T
CD
T
MD
= T
MC
+ T
CS
+ L
SD
* P
SD
T
CS
= T
CD
– L
SD
*P
SD
The parameters T
MD
and T
MC
apply to module designs. Module designers should minimize T
MC
, and then
arrange that T
MD
satisfies the relation T
MD
= T
MC
+ T
CD
.
Carrier board located PCI device Slot board located PCI device
LSD Length: slot card connector pin to slot card device. The following definitions and equations apply:
Fixed by PCI Local Bus Specification at 2.5 inches (units of time/length)
Determined by slot card PCB design; typical value is 160ps/inch.