MAX14500 Datasheet, PDF (22/41 Pages) Maxim Integrated Products – Hi-Speed USB-to-SD Card Readers with Bypass

Hi-Speed USB-to-SD Card
Readers with Bypass
PASS THRU
IF ASLEEP
REQUEST
TO ENTER CARD
READER
IF AWAKE
• DISCONNECT SD
SWITCHES FOR CARD READER
• ENUMERATE SD CARD
• OPEN USB SWITCHES
• ASSERT BUSY
• SET BUSY FLAG
• ENUMERATE PC
CARD READER
(TRANSFER DATA)
REQUEST
TO SLEEP OR
PASS THRU
SD COMMAND
IN PROGRESS
NO SD COMMAND IN PROGRESS
• DEENUMERATE PC
• CLOSE USB SWITCHES
• DEENUMERATE SD CARD
• RESTORE SD SWITCHES TO I²C SETTINGS
• DEASSERT BUSY
• CLEAR BUSY FLAG
Figure 9. Card Reader Flow Chart
go to sleep. Because the BUSY output (BSY bit in I²C)
indicates Card Reader mode, the host µP may monitor
this output after commanding a mode change to deter-
mine when the change takes place (Figure 9). If the host
requests the other SD card to enter Card Reader mode,
the busy flag deasserts and reasserts to let the host
know that the change took place.
Simple Control (I2C_SEL = Low)
The MAX14500–MAX14503 feature a very simple con-
trol scheme for entering Card Reader mode that
requires a single logic (GPIO) from the host µP. The
simple control may only be used with the single SD port
versions. When I2C_SEL is connected low at startup,
the MODE input controls whether the device is in Pass
Thru or Card Reader mode. Driving MODE low enables
Pass Thru mode (Figure 10), and the host µP has a
direct connection to the SD card and USB connector
through internal analog switches. Driving MODE high
enables Card Reader mode between SD card 1 and
the PC through the USB connector (Figure 11).
BERR/INT functions as the bridge error output BERR
that asserts for card reader errors. Interrupts are not
enabled, the clock source is set to the default as
defined by the part number, and the BERR and BUSY
outputs are active. Upon MODE transitioning high, SD
card 1 connects to the USB connector in Card Reader
mode and BUSY asserts low. The BUSY output indi-
cates that the device is in Card Reader mode. BUSY
may be important to the host µP, as the time to com-
plete enumeration/de-enumeration may take a long
time (> 100ms).
I²C Control (I2C_SEL = High)
The MAX14500–MAX14503 feature I²C control that
allows access to internal registers for complete control
over configuration, SD port analog switches, interrupts,
clock configuration, advanced power-on states, and
error status. I²C control uses I²C to serially program the
MAX14500–MAX14503 to be in Card Reader or Pass
Thru mode, and allows either SD card to be connected
in Card Reader mode. While a SD card is connected in
Card Reader mode, the other SD port analog switches
can be independently controlled serially through I²C.
Using the I²C bus to put the device to sleep minimizes
the supply current while maintaining control over the
SD port switches.
22 ______________________________________________________________________________________