Document Number: 001-87710 Rev. *A Page 3 of 27
Functional Overview
SD2™ is a USB 2.0 High Speed mass-storage controller
providing the latest SD/MMC support. SD2 complies with the SD
Specification, Version 3.0, and the MMC Specification, Version
4.41.
SD2 offers the following access paths among USB and mass
storage ports:
■A USB-port (U-Port) supporting USB 2.0 peripheral
■Two mass-storage ports (S0-Port and S1-Port) supporting
mass-storage devices. Following are the possible configura-
tions for the two mass-storage ports:
❐SD and MMC
❐SD and SD
❐MMC and MMC
❐SD and SDIO
❐MMC and SDIO
❐SDIO and SDIO
Combinations of these accesses can happen independently or
in an interleaved manner.
The SD2 complies with the USB 2.0 specification.
USB Interface (U-Port)
SD2 offers the following features:
■Supports USB peripheral functionality compliant with the USB
2.0 Specification
■Supports up to 16 IN and 16 OUT endpoints.
■Supports the USB 2.0 Streams feature. It also supports USB
Attached SCSI (UAS) device class to optimize mass-storage
access performance.
■As a USB peripheral, SD2 supports UAS and Mass Storage
Class (MSC) peripheral classes.
■When the USB port is not in use, the PHY and transceiver may
be disabled for power savings.
Figure 1. USB Interface Signals
Mass-Storage Support (S-Port)
The SD2 storage interface port supports the following
specifications:
■SD Specification, Version 3.0
■Multimedia Card-System Specification, MMCA Technical
Committee, Version 4.4
■SDIO Host controller compliant with SDIO Specification
Version 3.00
I2C Interface
SD2 has an I2C interface compatible with the I2C Bus
Specification Revision 3. Because SD2’s I2C interface is capable
of operating only as I2C master, it may be used to communicate
with other I2C slave devices. For example, SD2 may boot from
an EEPROM connected to the I2C interface, as a selectable boot
option.
SD2’s I2C master controller also supports multi-master mode
functionality.
The power supply for the I2C interface is VIO5, which is a
separate power domain from the other serial peripherals. This is
to allow the I2C interface the flexibility to operate at a different
voltage than the other serial interfaces.
The I2C controller supports bus frequencies of 100 kHz,
400 kHz, and 1 MHz. When VIO5 is 1.2 V, the maximum
operating frequency supported is 100 kHz. When VIO5 is 1.8 V,
2.5 V, or 3.3 V, the operating frequencies supported are 400 kHz
and 1 MHz. The I2C controller supports the clock stretching
feature to enable slower devices to exercise flow control.
Both SCL and SDA signals of the I2C interface require external
pull-up resistors. These resistors must be connected to VIO5.
UART Interface
The UART interface of SD2 supports full-duplex communication.
It includes the signals noted in Table 1.
The UART is capable of generating a range of baud rates, from
300 bps to 4608 Kbps, selectable by the firmware. If flow control
is enabled, then SD2’s UART only transmits data when the CTS
input is asserted. In addition to this, SD2’s UART asserts the
RTS output signal, when it is ready to receive data.
I2S Interface
SD2 has an I2S port to support external audio codec devices.
SD2 functions as I2S Master as transmitter only. The I2S
interface consists of four signals: clock line (I2S_CLK), serial
data line (I2S_SD), word select line (I2S_WS), and master
system clock (I2S_MCLK). SD2 can generate the system clock
as an output on I2S_MCLK or accept an external system clock
input on I2S_MCLK.
SD3
VBATT
VBUS
USB Interface
D-
D+
Table 1. UART Interface Signals
Signal Description
TX Output signal
RX Input signal
CTS Flow control
RTS Flow control