Specifications
©Copyright 2001-2013 SD Group (Panasonic, SanDisk, Toshiba) and SD Card Association
Physical Layer Simplified Specification Version 4.10
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4.2.4 Bus Signal Voltage Switch Sequence
4.2.4.1 Initialization Sequence for UHS-I
Figure 4-5 shows sequence of commands to perform voltage switch and Figure 4-6 shows initialization
flow chart for UHS-I hosts. Red and yellow boxes are new procedure to initialize UHS-I card.
Figure 4-5 : ACMD41 Timing Followed by Voltage Switch Sequence
Figure 4-6 : UHS-I Host Initialization Flow Chart
When signaling level is 3.3V, host repeats to issue ACMD41 with HCS=1 and S18R=1 until the response
indicates ready. The argument (HCS and S18R) of the first ACMD41 is effective but the all following
ACMD41 should be issued with the same argument. If Bit 31 indicates ready, host needs to check CCS
and S18A. The card indicates S18A=0, which means that voltage switch is not allowed and the host
needs to use current signaling level. S18A=1 means that voltage switch is allowed and host issues
CMD11 to invoke voltage switch sequence. By receiving CMD11, the card returns R1 response and start
voltage switch sequence. No response of CMD11 means that S18A was 0 and therefore host should not
have sent CMD11. Completion of voltage switch sequence is checked by high level of DAT[3:0]. Any bit of
DAT[3:0] can be checked depends on ability of the host.
S18A=0 (No Switch)
S18A=1 (Switch)
ACMD41 HCS=1, S18R=1
Check
busy
D31=0 (busy)
Check S18A
Voltage Switch Sequence
Switch to SDR12 timing
D31=1 (Completed)
No Response
CMD0
CMD8
CMD2
CMD3
CMD6
Function Group 3
Driver Strength
Power Cycle
CMD7
CMD6
Function Group 1, 4
CMD19
UHS-I Card?
Power Limit
Tuning
No
Yes
UHS-I Mode1.8V Signal
CMD11
ACMD6
Complete?
No
Yes
4-bit mode
Error?
No
Switch Error
Yes
Check Resp.
No Response
Get Response
UHS-I Mode
Check CCS
CCS=0 (SDSC)
CCS=1 (SDHC/SDXC)
CMD42
CMD55 R1 CMD41 R3 CMD55 R1 CMD41 R3 Voltage Switch CMD2 R2
Bit 31: Busy
Bit 30: CCS Invalid
Bit 24: S18A Invalid
Bit 31: Ready
Bit 30: CCS=1
Bit 24: S18A=1
Repeat ACMD41
The Last ACMD41
Bit 30: HCS=1
Bit 24: S18R=1
CMD11 R1