AN 509: Multiplexing SDIO Devices Using Altera MAX Series

ID 683683
Date 9/22/2014

1.1. Using Multiple SD Devices

It may often be required for an SD host controller with a single SD interface to support more than one SD device. The SD protocol and standards recommend doing this using one of following two methods:

  • Use a bidirectional multiplexer between the SD host and the multiple SD devices and use this multiplexer to multiplex the data lines. This is performed while the clock line is connected to each of the multiple SD devices.
  • Retain the data lines connected to the multiple SD devices while multiplexing the unidirectional clock line.

This design example uses the second method described above.

Figure 1. Implementing a Clock-Based SD MUX