Kontron CPCI Generic backplane - Manual (Page 19)

CPCI Backplane General
ID 24229, Rev. 01 © 2002 PEP Modular Computers GmbH Page 5
2. Clocks
The CompactPCI system slot drives five buffered clocks, while every adapter slot receives its
specific clock.
The 6-slot and 8-slot versions are provided with individual clock timings for the three slots on
the opposite end of the backplane. The remaining slots are assigned one clock for each two
slots.
Figure 2: Backplane Clock
Assignment (3U backplanes)
The system slot provides clock
signals for all the PCI peripherals
in the system, including devices
on the system slot board. Periph-
eral boards are provided with
clock signals via the Compact-
PCI backplane.
The 8-slot backplanes are pro-
vided with a diode termination
according to the CompactPCI
Specification.
Figure 3: Backplane Clock
Assignment (6U backplanes)
Clock skew is the difference
between the maximum and mini-
mum propagation delay of any
PCI clock signal. There are two
different types of clock skew:
backplane and system slot board
clock skew.
The two concepts of backplane
and system slot board clock
skew are explained in the follow-
ing.
2.1 Backplane Clock Skew
A CompactPCI backplane provides the distribution of clock signals for all of the board slots in
the system. The differences in the trace routing and net topologies contribute to skew and also
define the longest clock delay. Particular attention is paid by the PEP Modular Computers sys-
tem design to meet overall system clock skew requirements namely through simulation, test-
ing, and qualification.
Clock numbering:
2 1 3 4* 5**
6-slot/8-slot backplanes only
8-slot backplanes only *
**
Clock numbering:
2 1 3 4 5 6 7