SCES795C
– SEPTEMBER 2010 – REVISED FEBRUARY 2011
SETTING UP THE SIM INTERFACE
The TXS02326 supports both Class C (1.8V) or Class B (2.95V) SIM cards. In order to support these cards
types, the interface on the SIM side needs to be properly setup. After power up, the system should default to
SIM1 card. The following sequence outlines a rudimentary sequence of preparing the SIM1 card interface:
Configure the SIM1 regulator to 1.8V by asserting B1 = 0 in the SIM Interface Control Register (08h). The
system by default should start in 1.8V mode.
Configure the OE signal by asserting B0 = 0 in the Device Control Register (0Eh). The default value
essentially disables the OE pin and the device is configured as an auto direction translator.
The baseband SIM interface is set to a LOW state.
Disable the SIM1 interface by asserting B2 = 0 and B3 = 0 in the SIM Interface Control Register.
Disable the SIM2 interface by asserting B6 = 0 and B7 = 0 in the SIM Interface Control Register.
VSIM1 voltage regulator should now be activated by asserting B0 = 1 in the SIM Interface Control Register.
Enable the SIM1 interface by asserting B2 = 1 and B3 = 1 in the SIM Interface Control Register.
The SIM1 interface (VSIM1, SIM1CLK, SIM1I/O) is now active. The TXS02326 relies on the baseband to
perform the power up sequencing of the SIM card. If there is lack of communication between the baseband
and the SIM card, the SIM1 interface must be powered-down and then powered up again through the
regulator by configuring it to 2.95V by asserting B1 = 1 in the SIM Interface Control Register.
SWITCHING BETWEEN SIM CARDS
The following sequence outlines a rudimentary sequence of switching between the SIM1 card and SIM2 card:
Put the SIM1 card interface into
“clock stop” mode then assert B2 = 1 and B3 = 0 in the SIM Interface Control
Register (08h). This will latch the state of the SIM1 interface (SIM1CLK, SIM1I/O, SIM1RST).
There can be two scenarios when switching to SIM2 card:
– SIM2 may be in the power off mode, B6 = 0 and B7 = 0 in the Status Register (04h). If SIM2 is in power
off mode, the SIM/UICC interface will need to be set to the power off state. In this case the baseband will
most likely need to go through a power up sequence iteration
– SIM2 may already be in the “clock stop” mode, B6 = 1 and B7 = 0 in the Status Register (04h). If SIM2 is
in
“clock stop” mode, the interface between the baseband and the device is set to the clock stop mode
levels that correspond to the SIM2 card interface.
After determining whether the SIM2 card is either in power off mode or clock stop mode, the SIM2 card
interface is then activated by asserting B6 = 1 and B7 = 1 in the SIM Interface Control Register (08h) and the
negotiation between the baseband and card can continue.
Switching from SIM2 to SIM1 done in the same manner.
AUTOMATIC SHUTDOWN
Both SIM card interfaces can be configured to automatically shut down upon disconnecting the battery. The
shutdown threshold BSIThreshold is configured in B3 of the Device Control Register (0Eh). Two threshold levels are
available for this configuration. When the BSI input level exceeds the BSIThreshold level that caused this
power-down, both SIM card interfaces will automatically be shut down. If the battery removal interrupt is enabled
through B2 of the Device Control Register, then an interrupt will be issued to the baseband on IRQ. This case
may happen if the user decides to remove the battery.
There are two scenarios for shutting down each SIM: SIMx is
“active”, or in “clock stop” mode. In clock stop
mode, when the debounce timer expires, the SIMx signals all go low immediately, then the regulator is disabled
one 32KHz cycle later. If SIMx is active, the signals go low and the regulator is disabled in a particular sequence
to be described in the next section.
The SIM2 interface can also be configured to automatically shut down via the SDN pin.
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