Secure Digital & MultiMedia Cards

Shown looking into card

CMD: Command / Response
DAT0...3: Data lines 0 to 3
CD: Card Detect
!CS: Chip Select (Active Low)
DI, DO: Data In, Data Out (SPI signals)

S: power supply; I: input;
O: output using push-pull drivers; PP: I/O using push-pull drivers
OD: open drain; NC: not connected (or logic high)

Notes

SD cards evolved from MM cards, and share most pins. The SD spec added a card detection signal to pin 1, the ability to use up to 4 data bits for higher data rates, and to work in SPI mode. If buying equipment, SD is preferable to MM, SmartMedia, or XD.

The voltage range covers 3 NiCd/NiMH cells (3V6), 2-cell alkaline cells (3V), or low voltage logic (3V3), but NOT 5V.

Pins 9 and 1 to 6 are on a 2.5 mm pitch, slightly smaller than the common 0.1" (2.54 mm) grid.
Pin 7 is 2.425 mm from Pin 6, and Pin 8 is 1.7 mm away from Pin 7.

The pin numbering for SD cards is correct, they really did put pin 9 next to pin 1.

SanDisk have documentation for their programming interface at their website, but not the software source code itself. After ringing around, it seems this is because they want between 5 and 6 thousand pounds as a licence fee and membership of the SD card organisation. They are worried that if everyone had source code to talk to the cards, then someone would eventually figure out how to break the protection. If this is so, then they are breaking one of the first rules of cryptography: A security system should not rely on people not knowing how it works. For example, anyone can find out how Chubb door locks work, but that does not tell them what shape the keys for any particular door. The Enigma machine mechanism was well understood but was useless without the right keys. Security should lie in the personal keys.

A quick web search revealed no links to any public domain code for reading SD cards. Not even for just using them as unencrypted storage devices. I have absolutely no wish to make any pirate copies of any music.

However, a look at the public specifications suggests it should not be too hard to write code to do the low-level access of reading and writing sectors.

http://www.sdcard.org/ are the official keepers of the spec, but don't have it for free download.

http://www.sandisk.com/oem_sd_memorycard.html

Connections

SD Card Electrical Characteristics

Figures from www.kingmax.com/product/storage/KDxxxSC.pdf, you should double check specs for your own card.
VCC = 2V7 to 3V6
Clock rate is up to 20 MHz.
Multiple cards can share clock and power rails but not data lines.

ABSOLUTE MAXIMUM RATINGS

The maximum rating is the limit value that must not be exceeded even for an instant. As long as you use the product within the maximum rating defined, no permanent damage will ever occur. However this does not guarantee normal logical operation.

Parameter	Symbol	Min.	Max.	Unit	Note
Supply Voltage	VCC	-0. 3	4. 6	V	ESD (contact Pads) is 44KV
Storage Temperature	TSTG	-40	85	C
Pull-up resistance for CMD	RCMD	10	100	kOhm	Prevent bus floating
Pull-up resistance for DAT	RDAT
Signal Line Capacitance	CL		250	pF	Fpp <5 MHz, 21 cards on bus
			1000	pF	Fpp <20 MHz, 7 cards on bus
Signal Card Capacitance	CCARD		10	pF
Maximum Signal line Inductances			16	nH	Fpp <20 MHz
Pull-up resistance inside card(Pin1)	RDAT3	10	90	kOhm	May be used for card detection SD card

Operating Range

Parameter	Symbol	Min.	Max.	Unit	Note
Supply Voltage	VCC	2.0	3.6	V	Supply Voltage Specified in OCR Register 2.7 to 3.6
VInput Low Voltage	VIL	Vss-0.3	0.25x VCC	V
VInput High Voltage	VIH	0.625x VCC	VCC +0.3V	V
Output Low Voltage	VOL	0.125x VCC		V	VIOL=100uA@VDD Min
Output High Voltage	VOH	0.75x VCC		V	VIOH= -100uA@VDD Min
Input Leakage Current		-10	10	uA
Output Leakage Current		-10	10	uA
Minimum Supply current			150	uA	At 0 Hz, 3.6 V Standby state
High Speed Supply current			80	mA	At 25 MHz, 3.6 V
FPP		0	25	MHz	CL<100 pF (7 Cards)
Clock Frequency identification Mode	FOD	0	400	KHz	CL<250 pF (21 Cards)
Clock Low time	tWL	10		ns	CL<100 pF(7 Cards)
Clock High time	tWH
Clock Rise time	tTLH
Clock Fall time	tTLH
Clock Low time	tWL	50		ns	CL<250 pF(21 Cards)
Clock High time	tWH
Clock Rise time	tTLH
Clock Fall time	tTLH
Input Set-up Time	tISU	5		ns	CMD, DAT Reference to CLK
Input Hold Time	tIH
Output Set-up Time	tOSU
Output Set-up Time	tOH

External Links:

• SPI mode loses some abilities from native MMC mode.
• Once placed in SPI mode after power-on and reset, a card stays in that mode.
• Micros that have SPI ports will generally use MMC cards in this mode to avoid lots of tedious bit-banging.
  

The last link above looks the best.