Atmel AT85DVK-07 Especificaciones descargar pdf (Pagina 79)

AT85C51SND3Bx

7632A–MP3–03/06

Table 92 shows the different peripherals (source or destination) ID number. These num-

bers are used to program the SID and the DID in the DFD.

Table 91. Data Flow Descriptor Content

Table 92. Peripheral ID Number

CRC Processor In order to verify integrity of data transferred through the DFC, a CRC calculation can be

enabled using DFCRCEN bit in DFCON. It consists in a 16-bit CRC which is the remain

der after transfer data (MSB first) is divided by G(X). Polynomial formula is: G(X) = X

+ X

+ 1.

CRC16 operates on channel 0 only.

After an hardware reset, the CRC value is 0x0000 but can be set to any initial value by

writing two bytes

(1)

(MSB first) in the DFCRC register.

At the end of the data flow transfer

(2)

, CRC is available to user by reading two bytes

(1)

(MSB first) from the DFCRC register.

Notes: 1. This double write or read sequence can be reset by clearing the CRCEN bit.

2. The CRC value is not reset at start-up of a new data transfer.

Null Device The null device is used to allow CRC calculation on some data transfer (see

Section “CRC Processor”). When selected as destination, the null device is always

ready and simply acknowledges and discards data coming from the source. When

Byte

Number

Byte

Mnemonic

Description

0 SID

Source Identifier

See Table 92 for peripheral ID number.

1 DID

Destination Identifier

See Table 92 for peripheral ID number.

2 DPS

Data Packet Size

Decimal value giving the packet size as 2

DPS

. DPS takes value from 0 (1-byte

packet size) to 13 (8192-byte packet size).

Packet size is limited to 8192 bytes in case of DPS value greater than 13

3 DFSH Data Flow Size

16-bit wide data leading to data flow size from 1 to 2

- 1 data packets.

Writing 0x0000 to this field enables continuous data flow.

4 DFSL

ID Number Peripheral

0 C51 RAM

1 USB Controller

2 Audio Controller 1

3 Audio Controller 2

4 PSI Controller

5 SPI Controller

6 SIO Controller

7 Nand Flash Controller

8 MMC/SD Controller

9 ≤ n ≤ 14 Reserved

15 Null Device

1 2 ... 74 75 76 77 78 79 80 81 82 83 84 ... 262 263

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