SanDisk SD-ROM, SD032, SD064, SD128 3.4 Bus Topology

The Card Status Register (CSR) transmits the card's status information to the host. The CSR is

defined in Section 4.10.1 in the SDA Physical Layer Specification, Version 2.00.

The SD Status Register (SSR) contains status bits that are related to the SD Card proprietary

features and may be used for future applications. The SD Status structure is described in

Section 4.10.2 in the SDA Physical Layer Specification, Version 2.00.

The 16-bit Relative Card Address (RCA) Register carries the card address published by the

card during the card identification process. Refer to Section 5.4 in the SDA Physical Layer

Specification, Version 2.00 for more information.

The Operation Conditions Register (OCR) stores a card's VDD voltage profile. Refer to

Section 5.1 of the SDA Physical Layer Specification, Version 2.00 for more information.

3.4 Bus Topology

The family of SanDisk SD products supports two communication protocols: SD and SPI. For

more details, refer to Section 3.5 of the SDA Physical Layer Specification, Version 2.00. Section

6 of the specification contains a bus circuitry diagram for reference.

NOTE: SD Card pin assignments are provided by the SDA Physical Layer Specification, Version

2.00; refer to Section 8.2.

SD Bus Mode Pin Assignment SPI Bus Mode Pin Assignment

# Function I/O Type Description Function I/O Type Description

1 CD/DAT31,2 push-pull Card Detect /

Data [bit 3] CS1input Chip Select (active low)

2 CMD push-pull Command /

Response DataIn input Host-to-Card

commands and data

3 VSS1 supply Supply Ground VSS1 supply Supply Ground

4 VDD supply Supply Voltage VDD supply Supply Voltage

5 CLK input Clock SCLK input Clock

6 VSS2 supply Supply Ground VSS2 supply Supply Ground

7 DAT0 push-pull Data [bit 0] DataOut output Card-to-Host Data and

Status

8 DAT12push-pull Data [bit 1] RSV Reserved

9 DAT22push-pull Data [bit 2] RSV Reserved

Notes:

1. At power up this line has a 50KOhm pullup enabled in the card. This resistor serves two

functions: Card Detection and Mode Selection. For Mode Selection, the host can drive the

line high or let it be pulled high to select SD mode. If the host wants to select SPI mode it

should drive the line low. For Card detection, the host detects that the line is pulled high.

This pull-up should be disconnected by the user, during regular data transfer, with the

SET_CLR_CARD_DETECT (ACMD42) command.

2. The extended DAT lines (DAT1-DAT3) are input on power up. They start to operate as DAT

lines after the SET_BUS_WIDTH command. It is the responsibility of the host designer to

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