MAX14500 Datasheet, PDF (18/41 Pages) Maxim Integrated Products – Hi-Speed USB-to-SD Card Readers with Bypass

Hi-Speed USB-to-SD Card
Readers with Bypass
Timing Diagrams (continued)
SDA
SCL
t_HD,STA
t_{LOW_I2C}
t_SU,DAT
t_{HIGH_I2C}
t_HD,DAT
t_{R_I2C}
t_{F_I2C}
START
CONDITION
Figure 6. I²C Timing Diagram
t_SU,STA
t_{R_I2C}
t_HD,STA
REPEATED
START CONDITION
t_{F_I2C}
t_BUF
t_SU,STO
STOP
START
CONDITION CONDITION
Detailed Description
The MAX14500–MAX14503 can be added to devices
that have an SD card slot and a USB full-speed port
(12Mbps) to provide a Hi-Speed USB path to an SD
card bypassing the host microprocessor (µP), allowing
for faster SD card transfers (Figures 1–4). Without the
MAX14500–MAX14503, a host µP with a full-speed USB
port moves data between an SD card and a host PC at
12Mbps when transferring data from an SD card
through USB. The host µP has additional overhead
because it has to accept data from the SD cards,
process the data by putting it in USB format, and then
transfer the data through the USB port. The MAX14500–
MAX14503 create an alternate path from the SD card to
USB, providing USB Hi-Speed capability. By bypassing
the host µP using the MAX14500–MAX14503, SD card
read and write operations are not limited by host µP
overhead and USB full-speed data rates.
The MAX14500–MAX14503 operate in Pass Thru and
Card Reader mode. In Pass Thru mode, the MAX14500–
MAX14503 are transparent to the host µP. All read and
write operations pass from the host µP SD port to the SD
card without modification. All of the features of the original
device are intact and there is no need to change firmware
in the host µP. In Card Reader mode, the SD card is con-
nected to the PC with the internal USB Hi-Speed card
reader, bypassing the host µP.
The MAX14500–MAX14503 can be controlled in two
ways. The simple control method uses a single output
from a µP or ASIC to select Pass Thru or Card Reader
mode. Only one SD card can be used as a Hi-Speed
USB card reader in simple control. I²C control allows
more configuration options and provides status informa-
tion along with error conditions and additional interrupts.
Two SD cards can be connected and each set of SD
port switches can be controlled independently (two SD
port version under I²C control). The state of I2C_SEL
must not change after V_IO is applied.
With I²C control, the I²C bus is used to read and write to
internal registers for configuration, error checking, con-
trol, and status reporting. The control and configuration
registers have various functions including wakeup, SD
card selection, interrupt enable, and SD switch settings.
The status registers give the status of errors, SD card
detection, power supplies, and interrupts. Putting the
MAX14500–MAX14503 to sleep puts the device into
Pass Thru mode. The state of SD port switches for card 1
and card 2 can be changed while in Pass Thru. Some
I²C commands are executed upon waking up or entering
Card Reader mode. For register settings that involve
Card Reader mode, (when in Sleep mode), program-
ming the I²C registers changes the values, but the
actions do not execute until the internal logic wakes up
or Card Reader mode is entered. The register map indi-
cates when register bit changes take effect.
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