Layout Notes - Intel PXA27 Series Design Manual

Figure 19-2. Connectivity USIM Card and PXA27x Processor USIM Interface Using nUEN
PXA27x
TXD_OE_N
Processor
USIM
Interface
19.4

Layout Notes

Voltage level of the PXA27x processor pads is set off-chip (externally to PXA27x processor). The
pads work at either 1.8 V or 3.0 V. When the USIM card and the PXA27x processor operate at
different voltage levels, the I/O voltage level of the USIM card must be at a voltage level the
PXA27x processor supports.
Warning: Exercise care when placing the PXA27x processor into deep sleep mode. The voltage control
signals are powered from the VCC_IO power domain. In deep sleep mode, this power is turned off.
Powering off the voltage select signals (UVS0, nUVS1, and nUVS2) causes shorting of the power
supplies which are switched to provide power to the card. To prevent these electrical
problems, turn off the external power supply before (or at the same time) the PXA27x processor
enters deep sleep mode and correctly configures GPIOs prior to entering deep sleep mode.
Intel® PXA27x Processor Family Design Guide
PAD
RXD
nUEN
UCLK
nURST
UDET
USIM Controller Interface
UIO
20KΩ
VCC_USIM
1.8V or 3.0V
VCC_IO
§§
I/O
USIM
Card
VCC
GND
CLK_CARD
CARD_RST
CARD_DET
II:19-5