Revisiting SDIO

Latest Simplified Specifications - SD Association
https://www.sdcard.org/downloads/pls/simplified_specs/

SD Specifications, Part E1, SDIO Simplified Specification, Version 2.00, February 8, 2007
https://www.sdcard.org/developers/overview/sdio/sdio_spec/Simplified_SDIO_Card_Spec.pdf

SD Specifications, Part 1, Physical Layer Simplified Specification, Version 4.10, January 22, 2013
https://www.sdcard.org/downloads/pls/simplified_specs/part1_410.pdf

Secure Digital - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Secure_Digital

Secure Digital - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Secure_Digital#SDIO