SDI Technologies SDIO Card manual Card Detect Resistor, Timings, Combo Card 4-bit Control

SDIO Simplified Specification Version 2.00			©Copyright 2000-2007 SD Card Association
	I/O	Memory	Control Method
	Initialized	Not	CCCR
		Initialized
	Not	Initialized	ACMD6
	Initialized
	Initialized	Initialized	CCCR & ACMD6

Table 4-4 Combo Card 4-bit Control

As shown in Table 4-4, if only the I/O function of a combo card is active, only writing to the CCCR is required change the bus width mode. If only memory is active then ACMD6 is all that is needed to change bus widths. If both I/O and Memory are active then both CCCR and ACMD6 are needed to change the bus width. In the combo card, both the memory and I/O controllers shall be set to the same bus width

Note that Low-Speed SDIO cards support 4-bit transfer as an option. When communicating with a Low-Speed SDIO card, the host shall first determine if the card supports 4-bit transfer prior to attempting to select that mode.

If a Combo card supports the lock/unlock operation, it cannot change bus width of a locked card and returns an illegal command error to a bus width switch command. The host needs to unlock the card by CMD42 before changing bus width. This also implies that the host should not change bus width during initialization before managing a locked card.

4.6Card Detect Resistor

SD memory and I/O cards use a pull-up resistor on DAT[3] to detect card insertion. The procedure to enable/disable this resistor is different between SD memory and SDIO. SD memory uses ACMD42 to control this resistor while SDIO uses writes to the CCCR using CMD52. In the case of a combo card, both control locations exist and shall be managed by the host. For a combo card, the resistor is enabled only when both the memory and the I/O control registers have the resistor enabled. That is, after a power on, the host shall disable the resistor using ACMD42 to the memory controller or a CCCR write to the SDIO controller since the resistor enable is a logical AND of the two enables. Table 4-5 shows the effect of each resistor enable on the card’s resistor. After power-up, both locations default to resistor enabled. Note that after an I/O reset, the I/O resistor enable is not changed. Note that the SDIO Specification Version 1.00 required that both the SDIO and Memory resistor be disabled in order for the resistor to actually be disabled (logical OR of the 2 enables). Combo cards built to that specification require the host to disable both enables. It is recommended the host disable both enables of any combo card to avoid problems with the difference between 1.0 and current specification based cards.

I/O Resistor	Memory Resistor
Enabled	Enabled
Enabled	Disabled
Disabled	Enabled
Disabled	Disabled

Card Resistor

Resistor Connected

Resistor Disconnected

Resistor Disconnected

Resistor Disconnected

Table 4-5 Card Detect Resistor States

4.7Timings

This section is not included in the Simplified Specification.

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