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©Copyright 2000-2007 SD Card Association
SDIO Simplified Specification Version 2.00
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The host shall have the ability to manage power by calculating maximum current shown in the tuples
and control EMPC, EPS and IOEx not to exceed total current that the host can supply. If the host does
not have enough power to use the card, the host shall not enable the card.
11.3.2 Power Control Operation
A host reads the SMPC to see if the card supports Power Control additions. If so, the host checks SPS to see the
card’s support of Power Selection. If SMPC is set to 1, a version 1.10 host should set EMPC to 1.
Power Selection provides the host with the choice of two power modes for the function. A host that can supply
enough power to the card does not need to use Power Selection.
If SMPC is set to 1 and SPS is set to 1, the host can utilize Power Selection by setting EMPC to 1. If EPS is set
to 0 (default mode of the card), Higher Current Mode is selected. If EPS is set to 1, Lower Current Mode is
selected. For example, a wireless function may offer a power mode with reduced transmission range and
corresponding reduced current requirements. As the host knows how much current it can supply to the card, it
reads the appropriate tuples and decides whether or not to enable each function (with IOEX), and if so in what
Current Mode. The host shall verify that the total current required by the card shall not exceed the current of host
can supply. A version 1.10 host should read new tuples as shown in Table 11-1.