TOBY-R2 series - System integration manual
UBX-16010572 - R10
Design-in
Page 111 of 151
2.6.3.2
Guidelines for DDC (I2C) layout design
The DDC (I2C) serial interface requires the same consideration regarding electro-magnetic
interference as any other digital interface. Keep the traces short and avoid coupling with RF line or
sensitive analog inputs, since the signals can cause the radiation of some harmonics of the digital
data frequency.
2.6.4
SDIO interface
2.6.4.1
Guidelines for SDIO circuit design
☞
The functionality of the SDIO Secure Digital Input Output interface pins is not supported by
TOBY-R2 series modules “02” / "42" / "82" product versions: the pins should not be driven by any
external device.
TOBY-R2 series modules include a 4-bit Secure Digital Input Output interface (SDIO_D0, SDIO_D1,
SDIO_D2, SDIO_D3, SDIO_CLK, SDIO_CMD) designed to communicate with an external u-blox short
range Wi-Fi module.
Combining a u-blox cellular module with a u-blox short range communication module gives designers
full access to the Wi-Fi module directly via the cellular module, so that a second interface connected
to the Wi-Fi module is not necessary. AT commands via the AT interfaces of the cellular module
(UART, USB) allows full control of the Wi-Fi module from any host processor, because Wi-Fi control
messages are relayed to the Wi-Fi module via the dedicated SDIO interface.
☞
Further guidelines for SDIO interface circuit design will be described in detail in a successive
release of the System Integration Manual.
☞
Do not apply voltage to any SDIO interface pin before the switch-on of SDIO interface supply
source (V_INT), to avoid latch-up of circuits and allow a proper boot of the module.
☞
ESD sensitivity rating of SDIO interface pins is 1 kV (HMB according to JESD22-A114). Higher
protection level could be required if the lines are externally accessible and it can be achieved by
mounting a very low capacitance ESD protection (e.g. Tyco Electronics PESD0402-140 ESD), close
to accessible points.
☞
If the SDIO interface pins are not used, they can be left unconnected on the application board.
2.6.4.2
Guidelines for SDIO layout design
The SDIO serial interface requires the same consideration regarding electro-magnetic interference as
any other high speed digital interface.
Keep the traces short, avoid stubs and avoid coupling with RF lines / parts or sensitive analog inputs,
since the signals can cause the radiation of some harmonics of the digital data frequency.
Consider the usage of low value series damping resistors to avoid reflections and other losses in signal
integrity, which may create ringing and loss of a square wave shape.
