Product manual
or
Card Capacity (in bytes) (C_SIZE 1) s 2
(C_SIZE_MULT + 2)
s 2
READ_BL_LEN
.
The capacity is usually shown in MB and
Card Capacity (Megabyte) (C_SIZE 1) s 2
(C_SIZE_MULT 2)
s 2
READ_BL_LEN
/(1024 s 1024)
Using the CSD parameters given in this example, we get
Card Capacity (Megabyte) 3624 s 32 s 512/(1024 s 1024) 56.525 Megabytes
It is interesting to note that when a block length of 1024 bytes is used (READ_BL_
LEN 10), cards up to 2 GB can be specified, and with a block length of 2048 bytes
(READ_BL_LEN 11), cards up to 4 GB can be specified.
3.15 SD Card SPI Bus Protocol
!LL COMMUNICATIONS BETWEEN THE HOST AND THE CARD ARE CONTROLLED BY THE HOST -ESSAGES
IN THE 30) BUS PROTOCOL CONSIST OF COMMANDS RESPONSES AND TOKENS 4HE CARD RETURNS
A RESPONSE TO EVERY COMMAND RECEIVED AND ALSO A DATA RESPONSE TOKEN FOR EVERY WRITE
COMMAND
4HE 3$ CARD WAKES UP IN 3$ CARD MODE AND IT WILL ENTER THE 30) MODE IF ITS #3 LINE IS HELD
LOW WHEN A RESET COMMAND IS SENT TO THE CARD 4HE CARD CAN ONLY BE RETURNED TO THE 3$ MODE
AFTER A POWERDOWN AND POWERUP SEQUENCE
7HEN THE 30) MODE IS ENTERED THE CARD IS IN THE NONPROTECTED MODE WHERE #2# CHECKING IS
NOT USED #2# CHECKING CAN BE TURNED ON AND OFF BY SENDING COMMAND #2#?/.?/&& COM
MAND NAME #-$ TO THE CARD
3.15.1 Data Read
$ATA CAN BE READ IN EITHER SINGLE OR MULTIPLE BLOCKS 4HE BASIC UNIT OF DATA SIZE IS BLOCKS
DElNED BY lELD 2%!$?",?,%. OF THE #3$ REGISTER )N THIS BOOK WE SHALL BE USING ONLY
SINGLEBLOCK READS 3INGLEBLOCK READS ARE INITIATED BY ISSUING THE COMMAND 2%!$?3).',%?
",/#+ #-$ TO THE CARD !NY VALID ADDRESS CAN BE USED AS THE STARTING ADDRESS
3.15.2 Data Write
$ATA CAN BE WRITTEN IN EITHER SINGLE OR MULTIPLE BLOCKS !FTER RECEIVING A VALID WRITE COMMAND
THE CARD SENDS A RESPONSE TOKEN AND THEN WAITS FOR THE DATA BLOCK TO BE SENT FROM THE HOST 4HE
STARTING ADDRESS CAN BE ANY VALID ADDRESS !FTER RECEIVING A DATA BLOCK FROM THE HOST THE CARD
RETURNS A DATA RESPONSE TOKEN AND WRITES THE DATA ON THE CARD IF THE DATA CONTAINS NO ERRORS
132 Chapter 3
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