AS1543/44
Data Sheet - Detailed Description
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.
Each bit represents one of the input channels (VIN0 through VIN3/VIN7). Multiple channels can be selected for continu-
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).
Table 12. 16-Bit Shadow Register Format, AS1543
0
15
(MSB)
14
13
12
11
10
9
8
7
6
5
4
3
2
1
(LSB)
VIN0
VIN1
VIN2
VIN3
VIN4
VIN5
VIN6
VIN7
VIN0
VIN1
VIN2
VIN3
VIN4
VIN5
VIN6
VIN7
Table 13. 16-Bit Shadow Register Format, AS1544
0
15
(MSB)
14
13
12
11
10
9
8
7
6
5
4
3
2
1
(LSB)
VIN0
VIN1
VIN2
VIN3
VIN0
VIN1
VIN2
VIN3
VIN0
VIN1
VIN2
VIN3
VIN0
VIN1
VIN2
VIN3
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
Power On
DOUT: Dummy Conversion Result
DIN: Write to Control Register;
CSN Falling
Bit WRITE = 1;
Edge
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
Bit WRITE = 1, Bit SEQ = 0, Bit SHADOW = 0
Bit WRITE = 0
Bit WRITE = 0
Bit WRITE = 1
Bit SEQ = 0
Bit SHADOW = 0
DOUT: Conversion Result from
previously selected ADDR3:ADDR0
Channel
DOUT: Conversion Result from
previously selected ADDR3:ADDR0
Channel
Bit WRITE = 1,
Bit SEQ = 0,
Bit SHADOW = 0
CSN Falling
Edge
Bit WRITE = 0
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
CSN Falling
Edge
Exit this flow whenever WRITE = 1 and NOT (SEQ = 0, SHADOW = 0)
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