COM Express Carrier Type 2
Page 23 of 103
Design Guide
3.4.3
X1 Slot Example
Figure 4 PCIe x1 Reference Schematic
The example above shows COM Express PCIe lane 0 connected to the slot. Other lanes may be used
depending on what is available on the particular module being used.
No coupling caps are required on the PCIe data or clock lines. The PCIe TX series coupling caps on the
data lines are on the COM Express module. The PCIe RX coupling caps are up on the slot card.
Slot signals and REFCLK- (pins A13 and A14) are driven by the clock buffer. If there is only one
PCIe target on the carrier board, the clock buffer may be omitted and the slot REFCLOCK signals may
be driven directly by the COM Express module.
The slot reset signal (pin A11) is driven by a buffered copy of the COM Express PCI_RESET# signal. A
buffered copy of CB_RESET# could also be used. If the carrier board only has one or two target devices,
an unbuffered PCI_RESET# or CB_RESET# could be used.
The slot signals PRSNT1# and PRSNT2# are part of a mechanism defined in the PCI Express Card
Electromechanical Specification to allow hot plugged PCIe cards. However, most systems do not
implement the support circuits needed to complete hot plug capability. If used, the scheme works as
follows:
PRSNT1# (pin A1) is pulled low on the carrier board through R14. On the slot card, PRSNT1# is
routed to PRSNT2#_0 (pin B17). The state of slot pin B17 may be read back by the BIOS or system
software, if routed to an input port pin that can be read by software. If a slot card is present, this pin
reads back low; if the slot is empty, the pin will be read high. Software then uses this information to
apply power to the card. There is no standard input port pin defined by COM Express for this
function. For systems that are not trying to implement hot swap capability, it is not necessary to be
able to read back the state of the PRSNT2# pin. The figure above shows it being brought to a test
point.
Nets SMB_CK and SMB_DAT are sourced from COM Express module pins B13 and B14 respectively.
The SMBus supports card-management support functions. SMBus software can save the state of the
slot-card device before a Suspend event, report errors, accept control parameters, return status
information and card information such as a serial number. Support for the SMBus is optional on the
slot card.
Summary of Contents for COM Express Carrier
Page 1: ...COM Express Carrier Type 2 Design Guide October 2009 Confidential and Proprietary ...
Page 17: ...COM Express Carrier Type 2 Page 17 of 103 Design Guide Figure 1 COM Express Type 2 Connector ...
Page 36: ...Page 36 of 103 COM Express Carrier Type 2 Design Guide Table 5 SDVO Layout Requirement ...
