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•
The PRSNT signals are used to identify the lane width (x1) of the PCIe bus for the host
motherboard. The carrier ties the PRSNT1# and PRSNT2# signals together to accomplish
this. The host motherboard has pull-up and pull-down resistors on these signals so the
carrier does not require any other special configurations to enumerate as a single lane
PCIe device when plugged into a host PC.
•
The differential PCIe reference clock (PCIe_REFCLK_P/N) is routed directly to the JX3
header for SOM connectivity.
•
The PCI Express transmit lanes are AC coupled (DC blocking capacitors are included in
the signal path) on the development board as required by the PCI Express specification.
SOM Net Name:
PCIE_RX0P
PCIE_RX0N
PCIE_TX0P
PCIE_TX0N
PCIE_REFCLK_P
PCIE_REFCLK_N
PCIE_RST_N
2.6 FMC LPC Connector
A single Low Pin Count (LPC) FMC connector is implemented on the carrier board to support
FMC plug-in modules. The block diagram shows the MicroHeader connections to the FMC LPC
connectors. See Figure 7 – FMC Connections for topology overview.
When and FMC board is plugged in, the FMC_PRSNT_N and FMC_PRSNT_VADJ_N signals
are driven low per the FMC specification. The FMC_PRSNT_N signal is used to switch the
JTAG signals so the FMC card can be accessed through the JTAG interface. When a FMC
card is not present, FMC_PRSNT_N is pulled high via R104 and the JTAG interface is isolated
to the SOM only. See section
The FMC_PRSNT_VADJ_N signal can be used as an indicator to the SOM that an FMC device
has been attached. This signal is located per the table below:
SOM Net Name:
JX1_LVDS_2_N
There are four mounting holes in the FMC card area to facilitate secure FMC module mounting
and match the FMC specification. There are also no components directly under the FMC
mounting area on the top side of the board per the FMC specification.
Carrier
Net Name:
PCIE_RX0P
PCIE_RX0N
PCIE_TX0P
PCIE_TX0N
PCIE_REFCLK_P
PCIE_REFCLK_N
PCIE_RST_N
Table 7 – GTP Pin Locations for PCI Express
2.20, JTAG Interface.
Carrier Net Name:
FMC_PRSNT_VADJ_N
Table 8 – CP2104 Connections
14
JX3
Connection:
8
10
13
15
1
3
86
JX3 Pin:
25
22 Sept 2016
v1.1
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