SD Card Interface Description
SanDisk Secure Digital (SD) Card Product Manual, Rev. 1.9 © 2003 SANDISK CORPORATION
3-7
3.4.1. Power-up
The power up of the SD Card bus is handled locally in each SD Card and in the bus master.
Logic working level
Supply voltage
Supply ramp up time
Bus master supply voltage
ACMD
41
V
DD
max
Power up time
Initialization delay:
The maximum of
CMD2
N
CC
N
CC
N
CC
1 msec, 74 clock cycles
and supply ramp up time
Initialization sequence
V
DD
min
time
Time out value for initialization process = 1 sec
Optional repetitions of AMCD41
until no cards are responding
with busy bit set.
Valid voltage range
for commands CMD0,
15, 55, and ACMD41
Valid voltage
range for all
other commands
and memory
access.
ACMD
41
ACMD
41
Figure 3-5. Power-up Diagram
After power up, including hot insertion ( i.e., inserting a card when the bus is operating) the SD Card enters the
idle
state
. During this state the SD Card ignores all bus transactions until ACMD41 is received (ACMD command type
shall always precede with CMD55).
ACMD41 is a special synchronization command used to negotiate the operation voltage range and to poll the cards
until they are out of their power-up sequence. Besides the operation voltage profile of the cards, the response to
ACMD41 contains a busy flag, indicating that the card is still working on its power-up procedure and is not ready
for identification. This bit informs the host that the card is not ready. The host has to wait (and continue to poll the
cards, each one on his turn) until this bit is cleared. The maximum period of power up procedure of single card shall
not exceed 1 second.
Getting individual cards, as well as the whole SD Card system, out of
idle state
is up to the responsibility of the bus
master. Since the power up time and the supply ramp up time depend on application parameters such as the
maximum number of SD Card s, the bus length and the power supply unit, the host must ensure that the power is
built up to the operating level (the same level which will be specified in ACMD41) before ACMD41 is transmitted.
After power up, the host starts the clock and sends the initializing sequence on the CMD line. This sequence is a
contiguous stream of logical ‘1’s. The sequence length is the maximum of 1msec, 74 clocks or the supply-ramp-up-
time; the additional 10 clocks (over the 64 clocks after what the card should be ready for communication) is
provided to eliminate power-up synchronization problems.
Every bus master shall have the capability to implement ACMD41 and CMD1. CMD1 will be used to ask
MultiMediaCards to send their Operation Conditions. In any case the ACMD41 or the CMD1 shall be send
separately to each card accessing it through its own CMD line.
