Atmel AT85DVK-07 Spezifikationen PDF herunterladen (Seite 198)

198

AT85C51SND3Bx

7632A–MP3–03/06

Figure 92. Data Block Transmission Flows

Data Receiver

Configuration To receive data from the card the data controller must be configured in reception mode

by clearing the DATDIR bit in MMCON1 register.

Figure 93 summarizes the data stream reception flows in both polling and interrupt

modes while Figure 94 summarizes the data block reception flows in both polling and

interrupt modes, these flows assume that block length is greater than 16 Bytes.

Data Reception Reception is enabled by setting DATEN bit in MMCON1 register. The end of a data

frame (block(s) or stream) reception is signalled by the EOFI flag in MMINT register. In

multiblock mode, OEBI flag signals the reception of one block. These flags may gener

ate an interrupt request as detailed in Section “Interrupt”. When EOFI flag is set, 2 other

flags in MMSTA register: DATFS and CRC16S give a status on the frame received.

DATFS indicates if the frame format is correct or not: a valid End bit has been received,

and CRC16S indicates if the CRC16 computation is correct or not. CRC16S must by

reset by software by setting DCR bit in MMCON2 register. In case of data stream

CRC16S has no meaning and stays cleared. DATEN flag is cleared when EOFI is set.

According to the MMC specification data transmission from the card starts after the

access time delay (formally N

parameter) beginning from the End bit of the read com-

mand. To avoid any locking of the MMC controller when card does not send its data

(e.g. physically removed from the bus), a time-out timer must be launched to recover

Data Block

Transmission

FIFO Filling

write 16 data to MMDAT

FIFO Empty?

HFRS = 1?

FIFO Filling

write 8 data to MMDAT

No More Data

To Send?

Start Transmission

DATEN = 1

a. Polling mode

Data Block

Initialization

FIFO Filling

write 16 data to MMDAT

Start Transmission

DATEN = 1

Data Block

Transmission ISR

FIFO Filling

write 8 data to MMDAT

No More Data

To Send?

b. Interrupt mode

FIFO Empty?

HFRI = 1?

Mask FIFO Empty

HFRM = 1

Unmask FIFO Empty

HFRM = 0

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