MAX1258 Maxim Integrated Products, MAX1258 Datasheet - Page 24

• Manufacturer Part Number: MAX1258
• Description: Multichannel ADCs/DACs
• Manufacturer: Maxim Integrated Products

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The MAX1220–MAX1223/MAX1257/MAX1258 commu-
nicate between the internal registers and the external
circuitry through the SPI-compatible serial interface.
Table 1 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
register, DAC select register, reset register, and GPIO
command register, respectively.
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.
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.
12-Bit, Multichannel ADCs/DACs with FIFO,
Temperature Sensing, and GPIO Ports
24
______________________________________________________________________________________
Register Descriptions
Conversion Register
Setup Register
Table 4. Conversion Register*
*See below for bit details.
SCAN1
CHSEL3
CHSEL3
CHSEL2
CHSEL1
CHSEL0
SCAN1
SCAN0
NAME
TEMP
0
0
1
1
BIT
—
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
SCAN0
7 (MSB)
CHSEL2
0 (LSB)
0
1
0
1
BIT
6
5
4
3
2
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
Scans channels 0 through N.
Scans channels N through the highest
numbered channel.
S cans channel N r epeated l y. The AD C
aver ag ing reg i ster sets the numb er of
r esul ts.
N o scan. C onver ts channel N once onl y.
S et to one to sel ect conver si on r eg i ster .
Analog-input channel select.
Analog-input channel select.
Analog-input channel select.
Analog-input channel select.
Scan-mode select.
Scan-mode select.
Set to one to take a single temp-
erature measurement. The first
conversion result of a scan contains
temperature information.
CHSEL1
(CHANNEL N IS SELECTED BY
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
BITS CHSEL3–CHSEL0)
SCAN MODE
FUNCTION
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
AIN10
AIN11
AIN12
AIN13
AIN14
AIN15
AIN0
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
AIN7
AIN8
AIN9
( N )