AD7291 datasheet(17/21 Pages) AD

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Preliminary Technical Data

AD7291

Rev. PrC | Page 17 of 21

Figure 10. Command Mode Operation

AUTOCYCLE MODE

The AD7291 can be configured to convert continuously on a

programmable sequence of channels making it the ideal mode

of operation for system monitoring. These conversions take

place in the background approximately every 50 µs, and are

transparent to the master. The acquisition, and conversion

times combined for any channel should take approximately 3 µs

Typically, this mode is used to automatically monitor a selection

of channels with either the limit registers programmed to signal

an out-of-range condition via the alert function or the

minimum/maximum recorders tracking the variation over time

of a particular channel. Reads and writes can be performed at

any time (the ADC Result Register 0x01 contains the most

recent conversion result).

On power up, this mode is disabled. To enable this mode, write

to Bit D0 in the Command Register (0x00) and select the

desired channels for conversion by writing to the corresponding

channel bits D15 to D7. If more than one channel bit is set in

the configuration register, the ADC automatically cycles

through the channel sequence starting with the lowest channel

and working its way up through the sequence. Once the

sequence is complete, the ADC starts converting on the lowest

channel again, continuing to loop through the sequence until

this mode is exited. Once a conversion is completed the

conversion result is compared with the content of the Limit

Registers and Alert Status Registers are automatically updated.

If a violation of the Limit Registers is found the ALERT pin is

asserted with the polarity determined by bit D3 in the

Command Register.

If a command mode conversion is required while the autocycle

mode is active, it is necessary to disable the autocycle mode

before proceeding to the command mode. This is achieved by

setting Bit D0 of the command register to 1. When the

command mode conversion is complete, the user can re-enable

Autocycle mode by setting bit D0 to 1 in the command register.

In autocycle mode, the AD7291 does not enter partial power

down on receipt of a STOP condition, hence conversions and

alert monitoring will continue to function.

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