AT8xC51SND2C
User may abort command loading by setting and clearing the CTPTR bit in MMCON0
register which resets the write pointer to the transmit FIFO.
Figure 94. Command Transmission Flow
Command
Transmission
Load Command in
Buffer
MMCMD = index
MMCMD = argument
Configure Response
RESPEN = X
RFMT = X
CRCDIS = X
Transmit Command
CMDEN = 1
CMDEN = 0
Command Receiver
The end of the response reception is signalled to you by the EORI flag in MMINT regis-
ter. This flag may generate an MMC interrupt request as detailed in Section "Interrupt",
page 150. When this flag is set, 2 other flags in MMSTA register: RESPFS and CRC7S
give a status on the response received. RESPFS indicates if the response format is cor-
rect or not: the size is the one expected (48 bits or 136 bits) and a valid End bit has been
received, and CRC7S indicates if the CRC7 computation is correct or not. These Flags
are cleared when a command is sent to the card and updated when the response has
been received.
User may abort response reading by setting and clearing the CRPTR bit in MMCON0
register which resets the read pointer to the receive FIFO.
According to the MMC specification delay between a command and a response (for-
mally NCR parameter) can not exceed 64 MMC clock periods. To avoid any locking of
the MMC controller when card does not send its response (e.g. physically removed from
the bus), user must launch a time-out period to exit from such situation. In case of time-
out user may reset the command controller and its internal state machine by setting and
clearing the CCR bit in MMCON2 register.
This time-out may be disarmed when receiving the response.
143
4341D–MP3–04/05
ATMEL [ ATMEL ]
