Datasheet

AD7949 Data Sheet
Rev. D | Page 24 of 32
The register can be written to during conversion, during acquisi-
tion, or spanning acquisition/conversion, and is updated at the end
of conversion, t
CONV
(maximum). There is always a one deep
delay when writing the CFG register. Note that, at power-up, the
CFG register is undefined and two dummy conversions are
required to update the register. To preload the CFG register with a
factory setting, hold DIN high for two conversions. Thus
CFG[13:0] = 0x3FFF. This sets the AD7949 for the following:
• IN[7:0] unipolar referenced to GND, sequenced in order
• Full bandwidth for a one-pole filter
• Internal reference/temperature sensor disabled, buffer
enabled
• Enables the internal sequencer
• No readback of the CFG register
Table 9 summarizes the configuration register bit details. See
the Theory of Operation section for more details.
13 12 11 10 9 8 7 6 5 4 3 2 1 0
CFG INCC INCC INCC INx INx INx BW REF REF REF SEQ SEQ RB
Table 9. Configuration Register Description
Bit(s) Name Description
[13] CFG Configuration update.
0 = keep current configuration settings.
1 = overwrite contents of register.
[12:10] INCC Input channel configuration. Selection of pseudo bipolar, pseudo differential, pairs, single-ended, or temperature sensor. Refer
to the
Input Configurations section.
Bit 12
Bit 11
Bit 10
Function
0 0 X
1
Bipolar differential pairs; INx− referenced to V
REF
/2 ± 0.1 V.
0
1
0
Bipolar; INx referenced to COM = V
REF
/2 ± 0.1 V.
0
1
1
Temperature sensor.
1
0
X
1
Unipolar differential pairs; INx− referenced to GND ± 0.1 V.
1
1
0
Unipolar, INx referenced to COM = GND ± 0.1 V.
1 1 1
Unipolar, INx referenced to GND.
[9:7]
INx
Input channel selection in binary fashion.
Bit 9
Bit 8
Bit 7
Channel
0
0
0
IN0
0 0 1 IN1
… … …
1 1 1 IN7
[6]
BW
Select bandwidth for low-pass filter. Refer to the
Selectable Low-Pass Filter
section.
0 = ¼ of BW, uses an additional series resistor to further bandwidth limit the noise. Maximum throughput must also be reduced to ¼.
1 = full BW.
[5:3]
REF
Reference/buffer selection. Selection of internal, external, external buffered, and enabling of the on-chip temperature sensor.
Refer to the
Voltage Reference Output/Input
section.
Bit 5 Bit 4 Bit 3 Function
0 0 0 Internal reference, REF = 2.5 V output, temperature enabled.
0 0 1 Internal reference, REF = 4.096 V output, temperature enabled.
0
1
0
External reference, temperature enabled.
0 1 1 External reference, internal buffer, temperature enabled.
1
1
0
External reference, temperature disabled.
1 1 1 External reference, internal buffer, temperature disabled.
[2:1] SEQ
Channel sequencer. Allows for scanning channels in an IN0 to IN[7:0] fashion. Refer to the
Channel Sequencer section.
Bit 2 Bit 1 Function
0 0 Disable sequencer.
0 1 Update configuration during sequence.
1
0
Scan IN0 to IN[7:0] (set in CFG[9:7]), then temperature.
1 1 Scan IN0 to IN[7:0] (set in CFG[9:7]).
[0] RB Read back the CFG register.
0 = read back current configuration at end of data.
1 = do not read back contents of configuration.
1
X = don’t care.