MultiMediaCard (MMC)
Three other signals shown on the connector are COMM and the mechanical switches write protect (WP) and card detect (CD). WP and CD are both connected to COMM via a mechanical switch inside the socket when a device is inserted.
Three other signals shown on the connector are COMM and the mechanical switches WP and CD. When a device is inserted in the example schematic (Figure
SDCard devices have a write protect tab. Depending on the position of the tab, the WP signal may or may not be connected to the COMM signal. Connect the WP signal to a CPLD or other device capable of indicating to the driver software that the card is write protected. In this example, COMM is tied to a VCC and WP has a
The CD signal, MMC_DETECT, indicates to the MMC controller when a card is installed. It is used for both an SDCard socket and an MMC socket. Since the MMC socket does not have the mechanical CD switch, other measures must be taken to produce a card detect. Thus, the SDCard and MMC cases are discussed separately.
Note: While this schematic shows two ways to create a card detect, it is recommended that an SDCard socket be used if a card detect and write protection signal are desired even if only MMC devices are being used.
5.1.2.1SDCard Socket
When using Figure
SDCard sockets have a card detect switch internal to the socket. The CD signal is physically connected to the COMM signal. Connect the CD signal to a CPLD or other device capable of indicating to the driver software that a card has been inserted in the socket. In this example, COMM is tied to a VCC and CD has a
5.1.2.2MMC Socket
When using Figure
Unlike SDCard sockets, MMC sockets do not have a card detect or write protect switch. In order to implement this, a
PXA250 and PXA210 Applications Processors Design Guide |