10. Reset and Clocking > Clocking
90
PEB383 User Manual
July 25, 2011
Integrated Device Technology, Inc.
Confidential - NDA Required
10.2
Clocking
This section discusses clocking information for the PEB383’s PCIe and PCI Interfaces.
10.2.1
PCIe Clocking
The PCIe clocking is shown in
. The 100-MHz reference clock, PCIE_REFCLK_n/p, drives a
x(5/4) PLL to create a 125-MHz clock. The 125-MHz clock is further multiplied to create the Tx
parallel to serial conversion, and clocking out the Tx pins, PCIE_TXD_n/p (The receive data is clocked
into the PEB383 with the recovered clock. The elastic buffer operates on the recovered byte clock
(from K28.5) and the internal generated 125-MHz clock. The two clocks can vary by twice the ppm
tolerance of the reference clock tolerance on any one device (300ppm). Buffer overflow is prevented
by discarding skip characters.
Figure 26: PCIe Clocking
PCS
PHY
PCS
PCI E_REFCLK_p
PCI E_REFCLK_n
P LL
x(5/4)
8b10b encode
Parallel t o serial
Tx Diff erential
Driver
PCI E_TXD_p
PCI E_TXD_n
100 MHz
125 MHz
P LL
x20
2.5 GHz
Rx Diff erential
Rec eiv er
PCI E_RXD_p
PCI E_RXD_n
Cloc k recovery
Data rec ov ery
s erial to Parall el
Elas tic buf fer
Rec ov ered 2.5 GHz
10b8b decode
K 28.5
16
20
20
16
125 MHz (t o PCI e core)