Information Technology Reference
In-Depth Information
Table 5-6: MultiMediaCards have five configuration and status registers. Two of
the registers are unused in SPI mode.
Abbrevia-
tion
Name
Size
(bytes)
Purpose
OCR
Operation Conditions
Register
4
Bits 30..0 specify allowed power-supply
voltages.
Bit 31 is a status bit that equals 1 when the
power-up procedure has completed.
CID
Card Identification
16
Contains manufacturer and card
identification numbers, product name,
revision, serial number, and manufacturing
date.
CSD
Card Specific Data
16
Provides card-specific information. Includes
data relating to timing, data formats,
electrical specifications, write protection, and
error detecting.
cycles while holding DataIn high by writing FFh to the SPI buffer (SSP-
BUF). This macro generates eight clock cycles while holding DataIn high by
calling the WriteSPI library function:
#define mSend8ClkCycles() WriteSPI(0xFF);
Figure 5-1 shows the timing for block-read and block-write commands for
MultiMediaCards on an SPI bus. The following descriptions refer to the sig-
nals and times in the diagram.
A host can send a command immediately on bringing CS low to select the
card (NCS).
After receiving a command, a card delays between 8 and 64 clock cycles
before sending a response (NCR).
In a read operation, after sending a response, a card delays between 8 clock
cycles and a card-specific access time before sending the requested data
token (NAC). For commands where the card sends multiple data tokens,
the same wait time applies for the time between data tokens. The card-spe-
cific time is determined by values in the CSD register and the SCLK fre-
quency. Firmware that is waiting for a response can time out after any value
equal to or greater than the card-specific time.
Commands that request the contents of the CSD and CID registers are sim-
ilar in structure to commands that read from the storage media. A difference
Search WWH ::
Custom Search