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3.9.2 Card Detection
For SD/MMC Memory Card, detection of card insertion/removal by hardware is also supported.
Because a pull down resistor with about 470 K resistance which is impractical to embed in an I/O pad
is needed on the signal CD/DAT3, and it has to be capable of being connected or disconnected
dynamically onto the signal CD during initialization period, an additional I/O pad is needed to switch
on/off the pull down resistor on the system board. The scenario of card detection for SD/MMC Memory
Card is shown in Figure 3.9.2. Before SD/MMD Memory Card is inserted or powered on, SW1 and SW2
shall be opened for card detection of the host side. Meanwhile, pull down resistor R
shall attach onto the signal CD/DAT3 by the output signal RCDEN. In addition, SW3 on the card is
default to be closed. Upon insertion of SD/MMC Memory Card the signal CD/DAT3 will have a transition
from low to high. If SD/MMC Memory Card is removed then the signal CD/DAT3 will return to logic low.
After the card identification process, pull down resistor R
signal CD/DAT3 and SW3 on the card shall be opened for normal operation.
Since the scheme above needs a mechanical switch such as a relay on system board, it is not ideal
enough. Thus, a dedicated pin "INS" is used to perform card insertion and removal for SD/MMC. The pin
"INS" will connect to the pin "VSS2" of a SD/MMC connector.
Copyright © 2010 LG Electronics. Inc. All right reserved.
Only for training and service purposes
Figure 3.9.2 Card Detection for SD/MMC Memory Card
3. TECHNICAL BRIEF
on system board shall disconnect with the
CD
- 4 -
3. TECHNICAL BRIEF
on system board
CD
LGE Internal Use Only
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