Datasheet

Data Sheet AD7294
Rev. H | Page 31 of 48
CONFIGURATION REGISTER (0x09)
The configuration register is a 16-bit read/write register that
sets the operating modes of the AD7294. The bit functions of
the configuration register are outlined in Table 23 and Table 24.
On power-up, the configuration register is reset to 0x0000.
Sample Delay and Bit Trial Delay
It is recommended that no I
2
C bus activity occur when a con-
version is taking place; however, this may not be possible, for
example, when operating in autocycle mode. Bit D14 and Bit D13
in the configuration register are used to delay critical sample
intervals and bit trials from occurring while there is activity
on the I
2
C bus. On power-up, Bit D14 (noise-delayed sampling),
Bit D13 (noise-delayed bit trials), and Bit D3 (I
2
C filters) are
enabled (set to 0). This configuration is appropriate for low
frequency applications because the bit trials are prevented from
occurring when there is activity on the I
2
C bus, thus ensuring
good dc linearity perfor-mance. For high frequency input
signals, it may be desirable to have a known sampling point, thus
the noise-delayed sampling can be disabled by writing a 1 to Bit
D14 in the configuration register. This ensures that the
sampling instance is fixed relative to SDA, resulting in improved
SNR performance. If noise-delay samplings extend longer than 1
µs, the current conversion terminates. This termination can occur
if there are edges on SDA that are outside the I
2
C specification.
When noise-delayed sampling is enabled, the rise and fall times
must meet the I
2
C-specified standard. When D13 is enabled, the
conversion time may vary.
The default configuration for Bit D3 (enabled) is recommended
for normal operation because it ensures that the I
2
C requirements
for t
Of
(minimum)and t
SP
are met. The I
2
C filters reject glitches
shorter than 50 ns. If this function is disabled, the conversion
results are more susceptible to noise from the I
2
C bus.
Table 23. Configuration Register Bit Function Description D15 to D8
Channel
Bit D15 D14 D13 D12 D11 D10 D9 D8
Function
Reserved Noise-delayed
sampling. Use to
delay critical
sample intervals
from occurring
when there is
activity on the
I
2
C bus.
Noise-delayed
bit trials. Use to
delay critical bit
trials from
occurring when
there is activity
on the I
2
C bus.
Autocycle
mode
Pseudo
differential
mode for
V
IN
3/V
IN
4
Pseudo
differential
mode for
V
IN
1/V
IN
2
Differential
mode for
V
IN
3/V
IN
4
Differential
mode for
V
IN
1/V
IN
2
Setting
Enabled = 0 Enabled = 0 Enabled = 1 Enabled = 1 Enabled = 1 Enabled = 1 Enabled = 1
Disabled = 1 Disabled = 1 Disabled = 0 Disabled = 0 Disabled = 0 Disabled = 0 Disabled = 0
Table 24. Configuration Register Bit Function Description D7 to D0
Channel
Bit D7 D6 D5 D4 D3 D2 D1 D0
Function
2V
REF
range
for V
IN
4
2V
REF
range
for V
IN
3
2V
REF
range
for V
IN
2
2V
REF
range
for V
IN
1
I
2
C filters ALERT pin BUSY pin (D2 = 0),
clear alerts (D2 = 1)
Select ALERT
pin polarity
(active high/
active low)
Setting
Enabled = 1
Disabled = 0
Enabled = 1
Disabled = 0
Enabled = 1
Disabled = 0
Enabled = 1
Disabled = 0
Enabled = 0
Disabled = 1
Enabled
D2 = 1
D1 = 0
Disabled
D2 = 0
Enabled
D1 = 1 + D0 = 0
Disabled D1 = 0
Active high = 1
Active low = 0
Table 25. Alert/Busy Function Description
D2 D1 ALERT/BUSY Pin Functions
0 0 Pin does not provide any interrupt signal.
0 1 Configures pin as a busy output.
1 0 Configures pin as an alert output.
1 1 Resets the ALERT/BUSY output pin, the alert_flag bit in the conversion result register, and the entire alert status register (if any is
active). 1,1 is written to Bits[D2:D1] in the configuration register to reset the ALERT/BUSY pin, the alert_flag bit, and the alert status
register. Following this write, the contents of the configuration register read 1, 0 for Bit D2 and Bit D1, respectively, if read back.
Table 26. ADC Input Mode Example
D11 D10 D9 D8 Description
0 0 0 0 All channels single-ended
0 0 0 1 Differential mode on V
IN
1/V
IN
2
0 1 0 1 Pseudo differential mode on V
IN
1/V
IN
2