Datasheet

683

11011B–ATARM–21-Feb-12

SAM3N

34.6.4 Conversion FIFO

To provide flexibility and high efficiency, a 4 half-word FIFO is used to handle the data to be

converted.

As long as the TXRDY flag in the DACC Interrupt Status Register is active the DAC Controller is

ready to accept conversion requests by writing data in the DACC Conversion Data Register

(DACC_CDR). Data which cannot be converted immediately are stored in the DACC FIFO.

When the FIFO is full or the DACC is not ready to accept conversion requests, the TXRDY flag

is inactive.

Warning: Writing in the DACC_CDR register while TXRDY flag is inactive will corrupt FIFO

data.

34.6.5 Conversion Width

The WORD field of the DACC Mode Register allows the user to switch between half-word and

word transfer.

In half-word transfer mode only one 10-bit data item is sampled (DACC_MR[9:0]) per

DACC_CDR register write.

In word transfer mode each time the DACC_CDR register is written 2 data items are sampled.

First data item sampled for conversion will be DACC_CDR[9:0] and the second

DACC_CDR[25:16].

34.6.6 DAC Timings

The DAC startup time must be defined by the user in the STARTUP field of the DACC Mode

The DAC maximum clock frequency is 13 MHz, therefore the internal trigger period can be con-

figured through the CLKDIV field of the DACC Mode Register.

34.6.7 Write Protection Registers

In order to bring security to the DACC, a write protection system has been implemented.

The write protection mode prevents the write of the DACC Mode Register. When this mode is

enabled and the protected register is written an error is generated in the DACC Write Protect

Status Register and the register write request is canceled. When a write protection error occurs,

the WPROTERR flag is set and the address of the corresponding canceled register write is

available in the WPROTADRR field of the DACC Write Protect Status Register.

Due to the nature of the write protection feature, enabling and disabling the write protection

mode requires the use of a security code. Thus when enabling or disabling the write protection

mode, the WPKEY field of the DACC Write Protect Mode Register must be filled with the “DAC”

ASCII code (corresponding to 0x444143) otherwise the register write will be canceled.