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SDIO Emulation Over SPI Without SPI Mode in SDHC Master

IP.com Disclosure Number: IPCOM000197935D
Publication Date: 2010-Jul-22
Document File: 5 page(s) / 140K

Publishing Venue

The IP.com Prior Art Database

Abstract

SDIO (Secure Digital Input & Output) and SPI (Serial Peripheral Interface) are two completely different protocols. To be able to interact with a SDIO Host (Master), a device (Slave) would need to support SDIO mode (1 bit or 4 bit) or SPI mode. This paper provides technique to allow SDIO Host to interface directly with SPI slave thereby allowing it to send and receive packets. This is useful for any device (Slave) that does not support 1bit or 4 bit SDIO and only supports SPI interface.

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SDIO Emulation Over SPI Without SPI Mode in SDHC Master

Abstract:

SDIO (Secure Digital Input & Output) and SPI (Serial Peripheral Interface) are two completely different protocols. To be able to interact with a SDIO Host (Master), a device (Slave) would need to support SDIO mode (1 bit or 4 bit) or SPI mode.

This paper provides technique to allow SDIO Host to interface directly with SPI slave thereby allowing it to send and receive packets. This is useful for any device (Slave) that does not support 1bit or 4 bit SDIO and only supports SPI interface.

Introduction

SDIO is a popular interface to be able to interface a Host system with different memory cards like SD, MMC etc. SDIO can operated in SPI mode or 1/4/8-bit SD modes. One of the alternative ways to use SDIO is to do inter-chip communication that can support high baud rates (upto 400 Mbps in high speed 8-bit SD mode).

For inter-chip communication SD Host that supports SPI mode can directly interface with SPI slave however for a Host that does not support SPI mode, it can be challenging to interface SD host with SPI Slave. This paper describes techniques utilizing the SD protocol to be able to effectively interface a Non-SPI based SD Host with a SPI slave for inter-chip communication. One of the big advantage doing so is to utilize SPI slave interface to communicate with SD host(in 1 bit mode) instead of adding SDIO Device on the slave.

Interfacing

SD

Host with SPI Slave

Figure 1 shows the connections required to interface SDIO Host with SPI Slave. 

Figure 1 : Signal Connections to interface SDIO Host with SPI Slave

The SDIO host is programmed to be in 1 bit data transfer mode. SDIO host drives the clock to the SPI slave by connecting the SD Clock to SPI Clock. One of the GPIO’s (General purpose I/0) on the Host can be used to emulate Chip Select (also known as Slave Select) on the SPI Slave. The GPIO is used to select select SPI Slave and is a static signal during data transfer. Command signal (CMD in Figure1) on the SDIO Host can be connected to SPI MOSI (Master output slave input) to transmit data from SDIO Host to SPI Device. To receive data from SPI Slave, DAT0 on SDIO Host is connected to MISO (Master in slave out) on SPI.

Data Transmission – SDIO Host Writes to SPI Slave

The SDIO master is configured in 1-bit data transfer mode. Unlike for a communication with card where each command from the Host is acknowledged by response from the card, here SDIO master is programmed not to expect any response from SPI after the command is transmitted. This is important since SPI does not understand SD Commands. Figure 2 shows the behavior.

Figure 2 : Data transmission from SDIO Host to SPI Slave using Command Line

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