MAX1220 Datasheet, PDF (24/47 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
details the command byte, the registers, and the bit
names. Tables 4–12 show the various functions within
the conversion register, setup register, unipolar-mode
register, bipolar-mode register, ADC averaging regis-
ter, DAC select register, reset register, and GPIO com-
mand register, respectively.
Conversion Register
Select active analog input channels, scan modes, and
a single temperature measurement per scan by issuing
a command byte to the conversion register. Table 4
details channel selection, the four scan modes, and
how to request a temperature measurement. Start a
scan by writing to the conversion register when in clock
mode 10 or 11, or by applying a low pulse to the
CNVST pin when in clock mode 00 or 01. See Figures 6
and 7 for timing specifications for starting a scan with
CNVST.
A conversion is not performed if it is requested on a
channel or one of the channel pairs that has been con-
figured as CNVST or REF2. For channels configured as
differential pairs, the CHSEL0 bit is ignored and the two
pins are treated as a single differential channel.
Select scan mode 00 or 01 to return one result per sin-
gle-ended channel and one result per differential pair
within the selected scanning range (set by bits 2 and 1,
SCAN1 and SCAN0), plus one temperature result, if
selected. Select scan mode 10 to scan a single input
channel numerous times, depending on NSCAN1 and
NSCAN0 in the ADC averaging register (Table 9).
Select scan mode 11 to return only one result from a
single channel.
Setup Register
Issue a command byte to the setup register to config-
ure the clock, reference, power-down modes, and ADC
single-ended/differential modes. Table 5 details the bits
in the setup-register command byte. Bits 5 and 4
(CKSEL1 and CKSEL0) control the clock mode, acqui-
sition and sampling, and the conversion start. Bits 3
and 2 (REFSEL1 and REFSEL0) set the device for either
internal or external reference. Bits 1 and 0 (DIFFSEL1
and DIFFSEL0) address the ADC unipolar-mode and
bipolar-mode registers and configure the analog input
channels for differential operation.
Table 4. Conversion Register*
BIT
NAME
BIT
FUNCTION
—
7 (MSB) Set to one to select conversion register.
CHSEL3
6
Analog-input channel select.
CHSEL2
5
Analog-input channel select.
CHSEL1
4
Analog-input channel select.
CHSEL0
3
Analog-input channel select.
SCAN1
2
Scan-mode select.
SCAN0
1
Scan-mode select.
TEMP
0 (LSB)
Set to one to take a single temp-
erature measurement. The first
conversion result of a scan contains
temperature information.
*See below for bit details.
CHSEL3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
CHSEL2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
CHSEL1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
CHSEL0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
SELEC T ED
C H AN N EL
(N)
AIN0
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
AIN7
AIN8
AIN9
AIN10
AIN11
AIN12
AIN13
AIN14
AIN15
SCAN1
0
0
1
1
SCAN0
0
1
0
1
SCAN MODE
(CHANNEL N IS SELECTED BY
BITS CHSEL3–CHSEL0)
Scans channels 0 through N.
Scans channels N through the highest
numbered channel.
Scans channel N repeatedly. The ADC
averaging register sets the number of
results.
No scan. Converts channel N once only.
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