SMARC T335x Carrier Board Hardware Design Guide, Document Revision 1.2
2.9.2.1. Routing Considerations for SPI interface
The SPI signal length on the
SMARC
carrier board should be no longer
than 4.5 inches. It is recommended that you shorten your trace length as
much as possible to attain the best signal quality.
To reduce the length of the SPI trace, place the SPI device close to the
MXM 3.0 board
to
board interconnectors. Avoid stubs and minimize the
number of vias through the entire trace.
The following table shows the SPI signal layout and trace routing
guidelines.
Signal Name
Impedance Trace
Length
Length
Matching
Comments
SPI_MOSI
55Ohm
Max. 4.5
inches
Within one
inch per
segment
If there are two devices (SPI
ROM and Header) on carrier,
the routing is in daisy chain
topology.
SPI_MISO
SPI_CLK
SPI_CS#
SPI_POWER
Power for SPI devices. The trace width shall be minimally 20mil.