SanDisk SDSDH-1024 Product Manual - Page 71

Clock Control

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Revision 2.2 Chapter 4 - SD Card Protocol Description SanDisk SD Card Product Manual The host drives only one card, because it is not possible to control two cards or more if each of them has a different timing mode (Default and High-Speed). In order to satisfy severe timing, the CLK/CMD/DAT signal will be connected one-to-one between host and card. Maximum current consumption for SD cards operating in high-speed mode is 200mA (averaged over a period of one second). In High-speed Mode, VDD_R_CURR_MIN, VDD_W_CURR_MIN, VDD_R_CURR_MAX and VDD_W_CURR_MAX values in the CSD Register are meaningless. Also, in High-speed Mode, the TRAN_SPEED value in the CSD Register is 0_1011_010b (05Ah), which is equal to 50MHz. If necessary, the host will check the current consumption, indicated by the status returned by the Switch Function command (CMD6). 4.4.12 Command System SD Card commands CMD34-37, CMD50, CMD57 are reserved for SD command system expansion via the switch command. Switching between the various functions of the command-system function group, will change the interpretation and associated bus transaction (i.e., command without data transfer, single-block read, multiple-block write, etc.) of these commands. • When the standard command set (default function 0x0) is selected, the card will not recognize the commands and they will be considered illegal (as defined in the SD Physical Layer Specification v1.01). • When the vendor-specific (function 0xE) is selected, the commands are vendorspecific. They are not defined by this standard and may change for different card vendors. • When the mobile e-commerce (function 0x1) is selected, the behavior of these commands is governed by "Part A1: Mobile Commerce Extension Specification" of the SD Card specification. 4.5 Clock Control The host can use the SD Card bus clock signal to set the cards to energy-saving mode or control the bus data flow. The host is allowed to lower the clock frequency or shut it down. A few restrictions the host must follow include: • The bus frequency can be changed at any time under the restrictions of maximum data transfer frequency, defined by the SD Card and the identification frequency. − An exception is an ACMD41 (SD_APP_OP_COND). After issuing command ACMD41, either of the following procedures will be completed by the host until the card becomes steady: 1) Issue continuous clock in frequency range of 100 KHz-400 KHz, 2) If the host wants to stop the clock, the busy bit must be polled by the ACMD41 command at less than 50-msec intervals. © 2004 SanDisk Corporation 4-27 12/08/04

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Chapter 4 – SD Card Protocol Description
Revision 2.2
SanDisk SD Card Product Manual
© 2004 SanDisk Corporation
4-27
12/08/04
The host drives only one card, because it is not possible to control two cards or more if
each of them has a different timing mode (Default and High-Speed).
In order to satisfy
severe timing, the CLK/CMD/DAT signal will be connected one-to-one between host and
card.
Maximum current consumption for SD cards operating in high-speed mode is 200mA
(averaged over a period of one second). In High-speed Mode, VDD_R_CURR_MIN,
VDD_W_CURR_MIN, VDD_R_CURR_MAX and VDD_W_CURR_MAX values in the
CSD Register are meaningless. Also, in High-speed Mode, the TRAN_SPEED value in the
CSD Register is 0_1011_010b (05Ah), which is equal to 50MHz.
If necessary, the host will check the current consumption, indicated by the status returned
by the Switch Function command (CMD6).
4.4.12
Command System
SD Card commands CMD34-37, CMD50, CMD57 are reserved for SD command system
expansion via the switch command. Switching between the various functions of the
command-system function group, will change the interpretation and associated bus
transaction (i.e., command without data transfer, single-block read, multiple-block write,
etc.) of these commands.
•
When the standard command set (default function 0x0) is selected, the card will not
recognize the commands and they will be considered illegal (as defined in the SD
Physical Layer Specification v1.01).
•
When the vendor-specific (function 0xE) is selected, the commands are vendor-
specific. They are not defined by this standard and may change for different card
vendors.
•
When the mobile e-commerce (function 0x1) is selected, the behavior of these
commands is governed by “Part A1: Mobile Commerce Extension Specification” of the
SD Card specification.
4.5
Clock Control
The host can use the SD Card bus clock signal to set the cards to energy-saving mode or
control the bus data flow. The host is allowed to lower the clock frequency or shut it down.
A few restrictions the host must follow include:
•
The bus frequency can be changed at any time under the restrictions of maximum data
transfer frequency, defined by the SD Card and the identification frequency.
−
An exception is an ACMD41 (SD_APP_OP_COND).
After issuing command
ACMD41, either of the following procedures will be completed by the host until
the card becomes steady:
1) Issue continuous clock in frequency range of 100
KHz-400 KHz, 2) If the host wants to stop the clock, the busy bit must be polled
by the ACMD41 command at less than 50-msec intervals.