Rainbow Electronics AT89C51SND1C - Manual (Page 116)

116
AT8xC51SND1C
4109E–8051–06/03
Command Line
Controller As shown in Figure 81, the command line controller is divided in 2 channels: the com-
mand transmitter channel that handles the command transmission to the card through
the MCMD line and the command receiver channel that handles the response reception
from the card through the MCMD line. These channels are detailed in the following
sections.
Figure 81. Command Line Controller Block Diagram
Command Transmitter For sending a command to the card, user must load the command index (1 Byte) and
argument (4 Bytes) in the command transmit FIFO using the MMCMD register. Before
starting transmission by setting and clearing the CMDEN bit in MMCON1 register, user
must first configure:
• RESPEN bit in MMCON1 register to indicate whether a response is expected or not.
• RFMT bit in MMCON0 register to indicate the response size expected.
• CRCDIS bit in MMCON0 register to indicate whether the CRC7 included in the
response will be computed or not. In order to avoid CRC error, CRCDIS may be set
for response that do not include CRC7.
Figure 82 summarizes the command transmission flow.
As soon as command transmission is enabled, the CFLCK flag in MMSTA is set indicat-
ing that write to the FIFO is locked. This mechanism is implemented to avoid command
overrun.
The end of the command transmission is signalled to you by the EOCI flag in MMINT
register becoming set. This flag may generate an MMC interrupt request as detailed in
Section "Interrupt", page 124. The end of the command transmission also resets the
CFLCK flag.
CTPTR
MMCON0.4
CRPTR
MMCON0.5
MCMD
CMDEN
MMCON1.0
TX COMMAND Line
Finished State Machine
Data Converter
// -> Serial 5-Byte FIFO
MMCMD
TX Pointer
RFMT
MMCON0.1
CRCDIS
MMCON0.0
RESPEN
MMCON1.1
Data Converter
Serial -> //
RX Pointer
17 - Byte FIFO
MMCMD
CFLCK
MMSTA.0
CRC7
Generator
RX COMMAND Line
Finished State Machine
CRC7 and Format
Checker
CRC7S
MMSTA.2
RESPFS
MMSTA.1
EOCI
MMINT.5
EORI
MMINT.6
Command Transmitter
Command Receiver
Write
Read