Sd And Sdio Protocol Layout Notes - Intel PXA27 Series Design Manual

MultiMediaCard/SD/SDIO Card Controller
15.4.2.3

SD and SDIO Protocol Layout Notes

See Table 15-7
devices according to their respective specifications.
Table 15-7. SD/SDIO Card Pull-Up and Pull-Down Resistors
Signal
MMCMD
MMDAT<3:0>
1
WP
NOTE: This resistor is shown in the specification, but the value is not specified.
The 0.1 µF capacitor (C1) shown in
the SD/SDIO Card socket pin 3 (VDD) and pin 4 (VSS1).
COMM and the mechanical switches WP and CD signals are shown on the SD/SDIO Card socket
in Figure
and thus some SD/SDIO Card sockets do not have this signal. When a device is inserted in the
socket shown in
mechanical switches inside the socket. Ensure the WP and CD signals have debounce circuitry.
SD Cards have a write protect tab; the write protect tab is optional for SDIO Cards. Depending on
the position of the tab, the WP signal is either connected or not connected to the COMM signal. In
the example shown in
causes a rising edge to occur on the WP signal when the SD (or optional SDIO) Card's tab is in the
write protect position; the WP signal remains low when the tab is in the read/write position.
The mechanical switch CD signal functions in a similar manner as the switch in the socket closes to
connect COMM to the socket's CD signal when a device is inserted in the socket. In the example
shown in
edge to occur on the socket's CD signal when an SD/SDIO Card device is inserted in the socket.
Routing the CD of the socket signal to an appropriately configured GPIO input signal on the
PXA27x processor is used as a technique for the processor to detect (using the socket's mechanical
switch) that an SD/SDIO Card device insertion occurred. To wake up the PXA27x processor from
sleep mode using this technique, a GPIO input signal capable of waking up the processor must be
selected. Refer to the Intel
configuring GPIOs and GPIO sleep wake-up capabilities.
For sockets not having the COMM signal, connect the CD and WP signals to a CPLD or other
device capable of indicating to the driver software that the card is detected and write protected
respectively.
II:15-10
for the list of pull-up and pull-down resistors required for SD Card and SDIO Card
Pull-up or Pull-down
pull-up
pull-up
pull-up
15-4. COMM is optional (not required by the SD Card and SDIO Card specifications)
Figure 15-4, CD is connected to COMM and WP is connected to COMM using
Figure 15-4, COMM is tied to VCC and WP has a pull-down resistor. This
Figure 15-4, the sockets's CD signal has a pull-down resistor. This resistor causes a rising
®
PXA27x Processor Family Developers Manual for details on
Min Max
10 k Ω 100 k Ω Prevents bus floating
10 k Ω 100 k Ω Prevents bus floating
— — Any value sufficient to prevent bus floating
Figure 15-4 must be located within 0.512 inches (13 mm) of
®
Intel PXA27x Processor Family Design Guide
Remark