AD7997 datasheet(30/32 Pages) AD

30 / 32 page

AD7997/AD7998

Rev. 0 | Page 30 of 32

SECOND DATA BYTE

(LSBs)

FIRST DATA BYTE

(MSBs)

COMMAND/ADDRESS

POINT BYTE

7-BIT ADDRESS

SDA

SCL

SDA

SCL

Sr/P

ACK BY

AD7997/AD7998

ACK BY

AD7997/AD7998

ACK BY

MASTER

NACK BY

MASTER

ACK BY

AD7997/AD7998

Figure 33. Mode 2 Operation

SCL

7-BIT ADDRESS

COMMAND/ADDRESS

POINT BYTE

SDA

FIRST DATA BYTE

(MSBs)

SECOND DATA BYTE

(LSBs)

FIRST DATA BYTE

(MSBs)

SECOND DATA BYTE

(LSBs)

7-BIT ADDRESS

SDA

SCL

ACK BY

AD7997/AD7998

ACK BY

AD7997/AD7998

ACK BY

MASTER

ACK BY

MASTER

ACK BY

MASTER

ACK BY

AD7997/AD7998

RESULT FROM CH1

RESULT FROM CH2

A/A

Figure 34. Mode 2 Sequence Operation

MODE 3—AUTOMATIC CYCLE INTERVAL MODE

An automatic conversion cycle can be selected and enabled by

writing a value to the cycle timer register. A conversion cycle

interval can be set up on the AD7997/AD7998 by programming

the relevant bits in the 8-bit cycle timer register, as decoded in

Table 24. Only the 3 LSBs are used to select the cycle interval;

the 5 MSBs should contain 0s. When the 3 LSBs of the register

are programmed with any configuration other than all 0s, a

conversion takes place every X ms; the cycle interval, X,

depends on the configuration of these three bits in the cycle

timer register. There are seven different cycle time intervals to

choose from, as shown in Table 24. Once the conversion has

taken place, the part powers down again until the next conver-

sion occurs. To exit this mode of operation, the user must

program the 3 LSBs of the cycle timer register to contain all 0s.

To select a channel(s) for operation in the cycle mode, set the

corresponding channel bit(s), D11 to D4, of the configuration

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 the cycle timer register

contents are set to all 0s. This mode is useful for monitoring

signals, such as battery voltage and temperature, alerting only

when the limits are violated.

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