11

®

ADS7813

might be possible to use the rising edge of the DATACLK

signal. However, one extra clock period (not shown in

Figures 6, 7, and 8) is needed for the final bit.

The external DATACLK signal must be LOW or CS must

8). If this is not observed during this time, the output shift

register of the ADS7813 will not be updated with the

conversion result. Instead, the previous contents of the shift

register will remain and the new result will be lost.

Before reading the next three paragraphs, consult the Sensi-

tivity to External Digital Signals section of this data sheet.

This will explain many of the concerns regarding how and

when to apply the external DATACLK signal.

External DATACLK Active After the Conversion

The preferred method of obtaining the conversion result is to

provide the DATACLK signal after the conversion has been

completed and before the next conversion starts—as shown

in Figure 6. Note that the DATACLK signal should be static

before the start of the next conversion. If this is not ob-

served, the DATACLK signal could affect the voltage that

is acquired.

External DATACLK Active During the Next Conversion

Another method of obtaining the conversion result is shown

in Figure 7. Since the output shift register is not updated

until the end of the conversion, the previous result remains

valid during the next conversion. If a fast clock (

≥ 2MHz)

can be provided to the ADS7813, the result can be read

during time t

DATACLK signal is less likely to affect the conversion

result.

FIGURE 7. Serial Data Timing, External Clock, Clocking During the Next Conversion (EXT/INT HIGH,

CS LOW).

FIGURE 8. Serial Data Timing, External Clock, Clocking After the Conversion Completes and During the Next Conversion

(EXT/INT HIGH, CS LOW).

BUSY

CONV

t

24

t

4

t

5

DATACLK

t

25

1

2

n

n+1

15

16

DATA

MSB

Bit 14

Bit n

Bit n-1

Bit 1

LSB

34

BUSY

CONV

t

2

t

1

DATACLK

t

24

t

25

t

23

t

22

t

21

t

20

t

19

1

1

215

16

DATA

MSB

Bit 14

Bit 13

Bit 1

LSB

MSB