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AS1543/44

Data Sheet - D e t a i l e d D e s c r i p t i o n

Shadow Register

The shadow register is a 16-bit, write-only register. Data is loaded from pin DIN of the AS1543/44 on the falling edge of

SCLK. The data is transferred on pin DIN at the same time as a conversion result is read from the device. This requires

16 serial falling edges for the data transfer.

The information is clocked into the shadow register (provided bits SEQ (page 14) and SHADOW (page 14) were set to

0, 1 respectively), in the previous write to the control register.

ous cycling on each consecutive CSN falling edge after a write to the shadow register. To select a sequence of chan-

nels, the associated bit must be set for each analog input channel.

The AS1543/44 will continuously cycle through the selected channels in ascending order, beginning with the lowest

channel, until a write operation occurs (i.e., bit WRITE (page 14) is set to 1) with bits SEQ and SHADOW configured in

any way except 1, 0 (see Table 11 on page 17).

Direct Conversion (SEQ = 0, SHADOW = 0)

Figure 28 shows the normal flow of an ADC with multiple input channels selected, where each serial transfer selects

the next channel for conversion. In this mode of operation, the sequencer function is not used.

Figure 28. Bit SEQ = 0, Bit SHADOW = 0 Flowchart

Table 12. 16-Bit Shadow Register Format, AS1543

15

(MSB)

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

(LSB)

Table 13. 16-Bit Shadow Register Format, AS1544

15

(MSB)

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

(LSB)

Power On

DOUT: Dummy Conversion Result

DIN: Write to Control Register;

Bit WRITE = 1;

Select Coding, Range, SE/FDN, WEAK/TRIN and Power Mode;

Select Channel ADDR3:ADDR0 (see Table 5 on page 14) for

Conversion

Bit SEQ = 0, Bit SHADOW = 0

CSN Falling

Edge

Bit WRITE = 1, Bit SEQ = 0, Bit SHADOW = 0

Bit WRITE = 0

DOUT: Conversion Result from

previously selected ADDR3:ADDR0

Channel

DOUT: Conversion Result from

previously selected ADDR3:ADDR0

Channel

DIN: Write to Control Register;

Bit WRITE = 1;

Select Coding, Range, SE/FDN, WEAK/

TRIN and Power Mode;

Select Channel ADDR3:ADDR0 for

Conversion

Bit SEQ = 0, Bit SHADOW = 0

Bit WRITE = 1,

Bit SEQ = 0,

Bit SHADOW = 0

Bit WRITE = 0

Bit WRITE = 0

Bit WRITE = 1

Bit SEQ = 0

Bit SHADOW = 0

Exit this flow whenever WRITE = 1 and NOT (SEQ = 0, SHADOW = 0)

CSN Falling

Edge

CSN Falling

Edge