AD7785 datasheet(21/32 Pages) AD

21 / 32 page

AD7785

Rev. 0 | Page 21 of 32

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Figure 14. Filter Profile with Update Rate = 16.7 Hz

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Figure 15. Filter Profile with Update Rate = 242 Hz

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Figure 16. Filter Response at 470 Hz Update Rate

DIGITAL INTERFACE

The programmable functions of the AD7785 are controlled

using a set of on-chip registers. Data is written to these registers

via the serial interface of the device; read access to the on-chip

registers is also provided by this interface. All communications

with the device must start with a write to the communications

its communications register. The data written to this register

determines whether the next operation is a read operation or a

write operation and determines to which register this read or

write operation occurs. Therefore, write access to any of the

other registers on the part begins with a write operation to the

communications register followed by a write to the selected

continuous read mode is selected) starts with a write to the

communications register followed by a read operation from the

selected register.

The serial interface of the AD7785 consists of four signals: CS,

DIN, SCLK, and DOUT/RDY. The DIN line is used to transfer

data into the on-chip registers, and DOUT/RDY is used for

accessing from the on-chip registers. SCLK is the serial clock

input for the device, and all data transfers (either on DIN or

DOUT/RDY) occur with respect to the SCLK signal. The

DOUT/RDY pin operates as a data-ready signal also; the line

going low when a new data-word is available in the output

the data register to indicate when not to read from the device to

ensure that a data read is not attempted while the register is

being updated. CS is used to select a device. It can be used to

decode the AD7785 in systems where several components are

connected to the serial bus.

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