MAX1221 Datasheet, PDF (28/44 Pages) Maxim Integrated Products – 12-Bit, Multichannel ADCs/DACs with FIFO, Temperature Sensing, and GPIO Ports

12-Bit, Multichannel ADCs/DACs with FIFO,
Temperature Sensing, and GPIO Ports
Unipolar/Bipolar Registers
The final 2 bits (LSBs) of the setup register control the
unipolar-/bipolar-mode address registers. Set
DIFFSEL[1:0] = 10 to write to the unipolar-mode regis-
ter. Set bits DIFFSEL[1:0] = 11 to write to the bipolar-
mode register. In both cases, the setup command byte
must be followed by 1 byte of data that is written to the
unipolar-mode register or bipolar-mode register. Hold
CS low and run 16 SCLK cycles before pulling CS high.
Table 8. Unipolar/Bipolar Channel Function
UNIPOLAR-
MODE
REGISTER BIT
0
0
1
1
BIPOLAR-MODE
REGISTER BIT
0
1
0
1
CHANNEL PAIR
FUNCTION
Unipolar single-ended
Bipolar differential
Unipolar differential
Unipolar differential
If the last 2 bits of the setup register are 00 or 01, nei-
ther the unipolar-mode register nor the bipolar-mode
register is written. Any subsequent byte is recognized
as a new command byte. See Tables 6, 7, and 8 to pro-
gram the unipolar- and bipolar-mode registers.
Both registers power up at all zeros to set the inputs as
eight unipolar single-ended channels. To configure a
channel pair as single-ended unipolar, bipolar differen-
tial, or unipolar differential, see Table 8.
In unipolar mode, AIN+ can exceed AIN- by up to
V_REF. The output format in unipolar mode is binary. In
bipolar mode, either input can exceed the other by up
to V_REF / 2. The output format in bipolar mode is two’s
complement (see the ADC Transfer Functions section).
ADC Averaging Register
Write a command byte to the ADC averaging register to
configure the ADC to average up to 32 samples for
each requested result, and to independently control the
number of results requested for single-channel scans.
Table 9. ADC Averaging Register*
BIT NAME
BIT
—
7 (MSB)
—
6
—
5
AVGON
4
NAVG1
3
NAVG0
2
NSCAN1
1
NSCAN0
0 (LSB)
*See below for bit details.
FUNCTION
Set to zero to select ADC averaging register.
Set to zero to select ADC averaging register.
Set to one to select ADC averaging register.
Set to one to turn averaging on. Set to zero to turn averaging off.
Configures the number of conversions for single-channel scans.
Configures the number of conversions for single-channel scans.
Single-channel scan count. (Scan mode 10 only.)
Single-channel scan count. (Scan mode 10 only.)
AVGON
0
1
1
1
1
NAVG1
X
0
0
1
1
NAVG0
X
0
1
0
1
FUNCTION
Performs one conversion for each requested result.
Performs four conversions and returns the average for each requested result.
Performs eight conversions and returns the average for each requested result.
Performs 16 conversions and returns the average for each requested result.
Performs 32 conversions and returns the average for each requested result.
NSCAN1
0
0
1
1
NSCAN0
0
1
0
1
FUNCTION (APPLIES ONLY IF SCAN MODE 10 IS SELECTED)
Scans channel N and returns four results.
Scans channel N and returns eight results.
Scans channel N and returns 12 results.
Scans channel N and returns 16 results.
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