Specifications

©Copyright 2001-2013 SD Group (Panasonic, SanDisk, Toshiba) and SD Card Association
Physical Layer Simplified Specification Version 4.10
116
The following sections describe the CSD fields and the relevant data types. If not explicitly defined
otherwise, all bit strings are interpreted as binary coded numbers starting with the left bit first.
• TAAC
Defines the asynchronous part of the data access time.
TAAC bit position
code
2:0
time unit
0=1ns, 1=10ns, 2=100ns, 3=1µs, 4=10µs,
5=100µs, 6=1ms, 7=10ms
6:3
time value
0=reserved, 1=1.0, 2=1.2, 3=1.3, 4=1.5,
5=2.0,
6=2.5, 7=3.0, 8=3.5, 9=4.0, A=4.5, B=5.0,
C=5.5, D=6.0, E=7.0, F=8.0
7
reserved
Table 5-5: TAAC Access Time Definition
• NSAC
Defines the worst case for the clock-dependent factor of the data access time. The unit for NSAC is 100
clock cycles. Therefore, the maximal value for the clock-dependent part of the data access time is 25.5
k clock cycles.
The total access time N
AC
is the sum of TAAC and NSAC. It should be computed by the host for the
actual clock rate. The read access time should be interpreted as a typical delay for the first data bit of a
data block or stream.
• TRAN_SPEED
The following table defines the maximum data transfer rate per one data line - TRAN_SPEED:
TRAN_SPEED bit
code
2:0
transfer rate unit
0=100kbit/s, 1=1Mbit/s, 2=10Mbit/s,
3=100Mbit/s, 4... 7=reserved
6:3
time value
0=reserved, 1=1.0, 2=1.2, 3=1.3, 4=1.5,
5=2.0, 6=2.5, 7=3.0, 8=3.5, 9=4.0, A=4.5,
B=5.0, C=5.5, D=6.0, E=7.0, F=8.0
7
reserved
Table 5-6: Maximum Data Transfer Rate Definition
Note that for current SD Memory Cards, this field shall be always 0_0110_010b (032h) which is equal to
25 MHz - the mandatory maximum operating frequency of SD Memory Card.
In High-Speed mode, this field shall be always 0_1011_010b (05Ah) which is equal to 50 MHz, and
when the timing mode returns to the default by CMD6 or CMD0 command, its value will be 032h.