Kontron COMe Starterkit Eval T2 - Manual (Page 140)

COM Express Interfaces
2.22.7. SDIO Interface Multiplexed with GPIOs
SD Card support was added in COM.0 Rev. 2.0 as an alternative use for the GPIO pins. The
schematic below shows a multiplexer allowing the carrier to use the COM Express pins either as
GPIO or as an SD Card interface. In a dedicated application the multiplexer is not necessary – if
you just want an SD Card interface and no GPIO you can route the pins directly from the COM
Express connectors to the SD Card. It is important that the SD Cards are ESD protected.
The following notes apply to Figure 56: SDIO Interface Multiplexed with GPIOs below.
U19 is the switch device to determine the usage of the GPI0 to GPI3 and GPO0 to GPO3 coming
from the COM Express Module. When Jumper J39 is set to GND, SDIO is supported. When
J39 is open, GPIO is supported. Please verify that the Module used supports the intended
interface. To simplify the circuit, instead of installing U19, resistors R220 to R225, R227 and
R249 can be installed when only SDIO is necessary without the usage of GPIOs.
Maximum length for SDIO should be restricted to 3 inches to the SDIO connector. Additional EMI
or ESD measures might be applicable.
PICMG ® COM Express ® Carrier Board Design Guide Rev. 2.0 / December 6, 2013
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