SDMJ-32 SanDisk, SDMJ-32 Datasheet - Page 49

• Manufacturer Part Number: SDMJ-32
• Manufacturer: SanDisk
• Type: MultiMedia Cardr

Specifications of SDMJ-32

• Density: 32MByte
• Operating Supply Voltage (typ): 3.3V
• Operating Temperature (min): -25C
• Operating Temperature (max): 85C
• Package Type: MMC
• Mounting: Socket
• Pin Count: 7
• Operating Temperature Classification: Commercial
• Operating Supply Voltage (min): 2.7V
• Operating Supply Voltage (max): 3.6V
• Programmable: Yes
• Lead Free Status / RoHS Status: Compliant

Revision 1.3
© 2005 SanDisk Corporation
4.4.1
4.3
4.4
Clock Control
Cyclic Redundancy Codes
CRC7
The host can use the MultiMediaCard/RS-MultiMediaCard 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 Cyclic Redundancy Check (CRC) is intended to protect MultiMediaCard/RS-
MultiMediaCard commands, responses, and data transfer against transmission errors on its
bus. One CRC is generated for every command and checked for every response on the
CMD line. For data blocks, CRCs are generated for each DAT line per transferred block.
The CRC is generated and checked as shown in the following subsections.
The CRC7 check is used for all commands, all responses except type R3, and CSD and
CID registers. The CRC7 is a 7-bit value and is computed as follows:
All CRC registers are initialized to zero. The first bit is the most significant bit of the
corresponding bit string (of the command, response, CID or CSD). The degree n of the
polynomial is the number of CRC protected bits decreased by one. The number of bits to
be protected is 40 for commands and responses (n = 39), and 120 for the CSD and CID (n
= 119) registers.
• The bus frequency can be changed at any time (under the restrictions of maximum data
• It is an obvious requirement that the clock must be running for the card to output data
• The host is allowed to shut down the clock of a card that is busy; the card will
transfer frequency, defined by the MultiMediaCard/RS-MultiMediaCard and the
identification frequency).
or response tokens. After the last bus transaction, the host is required, to provide eight
clock cycles for the card to complete the operation before shutting down the clock.
Following is a list of various card bus transactions:
complete the programming operation regardless of the host clock. However, the host
must provide a clock edge for the card to turn off its busy signal. Without a clock edge
the card (unless previously disconnected by a deselect command -CMD7) will
permanently force the DAT line down.
−
−
−
−
A command with no response—eight clocks after the host command end bit.
A command with response—eight clocks after the card response end bit.
A read data transaction—eight clocks after the end bit of the last data block.
A write data transaction—eight clocks after the CRC status token.
generator polynomial: G(x) = x
M(x) = (first bit) * x
CRC[6...0] = Remainder [(M(x) * x
n
+ (second bit) * x
4-11
7
+ x
MultiMediaCard/RS-MultiMediaCard Product Manual
7
3
) / G(x)]
Chapter 4 – MultiMediaCard Protocol Description
+ 1
n-1
+...+ (last bit) * x
0
04/22/05