LG -A290 Service Manual page 43

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 KΩ 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.. Before SD/MMD Memory Card is inserted or powered on, SW1 and
SW shall be opened for card detection of the host side. Meanwhile, pull down resistor RCD on system board 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 RCD
on system board shall disconnect with the 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 "VSS"
of a SD/MMC connector.
DATA3 OUT
CD/DAT3 IN
LGE Internal Use Only
HOST
R
PU
SW1
PAD
R
PD
SW
Figure 3.9.2 Card Detection for SD/MMC Memory Card
10-90 K
PAD
470 Kohm
RCDEN
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3. TECHNICAL BRIEF
CARD
SW3
Only for training and service purposes