
MPC8640 and MPC8640D Integrated Host Processor Hardware Specifications, Rev. 3
Freescale Semiconductor
119
System Design Information
Local Bus—If parity is not used, tie LDP[0:3] to ground via a 4.7-k
Ω resistor, tie LPBSE to OVDD
via a 4.7-k
Ω resistor (pull-up resistor). For systems which boot from Local Bus
(GPCM)-controlled flash, a pull-up on LGPL4 is required.
SerDes—Receiver lanes configured for PCI Express are allowed to be disconnected (as would
occur when a PCI Express slot is connected but not populated). Directions for terminating the
20.5.1
Guidelines for High-Speed Interface Termination
This section provides the guidelines for high-speed interface termination.
20.5.1.1
SerDes Interface
The high-speed SerDes interface can be disabled through the POR input cfg_io_ports[0:3] and through the
DEVDISR register in software. If a SerDes port is disabled through the POR input the user cannot enable
it through the DEVDISR register in software. However, if a SerDes port is enabled through the POR input
the user can disable it through the DEVDISR register in software. Disabling a SerDes port through
software should be done on a temporary basis. Power is always required for the SerDes interface, even if
the port is disabled through either mechanism.
Table 72 describes the possible enabled/disabled scenarios
for a SerDes port. The termination recommendations must be followed for each port.
If the high-speed SerDes port requires complete or partial termination, the unused pins should be
terminated as described in this section.
Table 72. SerDes Port Enabled/Disabled Configurations
Disabled Through POR Input
Enabled Through POR Input
Enabled through DEVDISR
SerDes port is disabled (and cannot
be enabled through DEVDISR)
Complete termination required
(Reference Clock not required)
SerDes port is enabled
Partial termination may be required1
(Reference Clock is required)
1 Partial Termination when a SerDes port is enabled through both POR input and DEVDISR is determined by the SerDes
port mode. If the port is in
×8 PCI Express mode, no termination is required because all pins are being used. If the port
is in
×1/×2/×4 PCI Express mode, termination is required on the unused pins. If the port is in ×4 serial RapidIO mode,
termination is required on the unused pins.
Disabled through DEVDISR
SerDes port is disabled (through
POR input)
Complete termination required
(Reference Clock not required)
SerDes port is disabled after software
disables port
Same termination requirements as when the
port is enabled through POR input2
(Reference Clock is required)
2 If a SerDes port is enabled through the POR input and then disabled through DEVDISR, no hardware changes are
required. Termination of the SerDes port should follow what is required when the port is enabled through both POR
input and DEVDISR. See Note 1 for more information.
Note: