Atmel SAM4S Series, Предварительный информационный лист

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11100B–ATARM–31-Jul-12
SAM4S Series [Preliminary]
41.6.4 Conversion FIFO
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 into DACC Conversion Data Register . 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.
The WORD field of the DACC Mode Register allows the user to switch between half-word and
word transfer for writing into the FIFO.
In half-word transfer mode only the 16 LSB of DACC_CDR data are taken into account,
DACC_CDR[15:0] is stored into the FIFO.
DACC_CDR[11:0] field is used as data and the DACC_CDR[15:12] bits are used for channel
selection if the TAG field is set in DACC_MR register.
In word transfer mode each time the DACC_CDR register is written 2 data items are stored in
the FIFO. The first data item sampled for conversion is DACC_CDR[15:0] and the second
DACC_CDR[31:16].
Fields DACC_CDR[15:12] and DACC_CDR[31:28] are used for channel selection if the TAG
field is set in DACC_MR register.
Warning: Writing in the DACC_CDR register while TXRDY flag is inactive will corrupt FIFO
data.
41.6.5 Channel Selection
There are two means by which to select the channel to perform data conversion.
• By default, to select the channel where to convert the data, is to use the USER_SEL field of
the DACC Mode Register . Data requests will merely be converted to the channel selected
with the USER_SEL field.
• A more flexible option to select the channel for the data to be converted to is to use the tag
mode, setting the TAG field of the DACC Mode Register to 1. In this mode the 2 bits,
DACC_CDR[13:12] which are otherwise unused, are employed to select the channel in the
same way as with the USER_SEL field. Finally, if the WORD field is set, the 2 bits,
DACC_CDR[13:12] are used for channel selection of the first data and the 2 bits,
DACC_CDR[29:28] for channel selection of the second data.
41.6.6 Sleep Mode
The DACC Sleep Mode maximizes power saving by automatically deactivating the DACC when
it is not being used for conversions.
When a start conversion request occurs, the DACC is automatically activated. As the analog cell
requires a start-up time, the logic waits during this time and starts the conversion on the selected
channel. When all conversion requests are complete, the DACC is deactivated until the next
request for conversion.
A fast wake-up mode is available in the DACC Mode Register as a compromise between power
saving strategy and responsiveness. Setting the FASTW bit to 1 enables the fast wake-up
mode. In fast wake-up mode the DACC is not fully deactivated while no conversion is requested,
thereby providing less power saving but faster wake-up (4 times faster).