MAX1258 Maxim Integrated Products, MAX1258 Datasheet - Page 20

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

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Table 1. Command Byte (MSB First)
Write to the GPIOs (if applicable) by issuing a com-
mand byte to the appropriate register. Writing to the
MAX1220/MAX1221 GPIOs requires 1 additional byte
following the command byte. Writing to the MAX1257/
MAX1258 requires 2 additional bytes following the
command byte. See Tables 12–19 for details on GPIO
configuration, writes, and reads. See the GPIO
Command section. Command bytes written to the
GPIOs on devices without GPIOs are ignored.
The MAX1220–MAX1223/MAX1257/MAX1258 power up
with all blocks in shutdown (including the reference). All
registers power up in state 00000000, except for the
setup register and the DAC input register. The setup
register powers up at 0010 1000 with CKSEL1 = 1 and
REFSEL1 = 1. The DAC input register powers up to
FFFh when RES_SEL is high and powers up to 000h
when RES_SEL is low.
The MAX1220–MAX1223/MAX1257/MAX1258 ADCs
use a fully differential successive-approximation regis-
ter (SAR) conversion technique and on-chip track-and-
hold (T/H) circuitry to convert temperature and voltage
signals into 12-bit digital results. The analog inputs
accept both single-ended and differential input signals.
Single-ended signals are converted using a unipolar
transfer function, and differential signals are converted
using a selectable bipolar or unipolar transfer function.
See the ADC Transfer Functions section for more data.
When addressing the setup, register bits 5 and 4 of the
command byte (CKSEL1 and CKSEL0, respectively)
control the ADC clock modes. See Table 5. Choose
12-Bit, Multichannel ADCs/DACs with FIFO,
Temperature Sensing, and GPIO Ports
X = Don’t care.
*Only applicable on the MAX1220/MAX1221/MAX1257/MAX1258.
20
REGISTER NAME
Conversion
Setup
ADC Averaging
DAC Select
Reset
GPIO Configure*
GPIO Write*
GPIO Read*
No Operation
______________________________________________________________________________________
BIT 7
1
0
0
0
0
0
0
0
0
Power-Up Default State
CHSEL3
BIT 6
ADC Clock Modes
1
0
0
0
0
0
0
0
12-Bit ADC
CHSEL2
CKSEL1
BIT 5
1
0
0
0
0
0
0
CHSEL1
CKSEL0
AVGON
BIT 4
between four different clock modes for various ways to
start a conversion and determine whether the acquisi-
tions are internally or externally timed. Select clock
mode 00 to configure CNVST/AIN_ to act as a conver-
sion start and use it to request internally timed conver-
sions, without tying up the serial bus. In clock mode 01,
use CNVST to request conversions one channel at a
time, thereby controlling the sampling speed without
tying up the serial bus. Request and start internally
timed conversions through the serial interface by writ-
ing to the conversion register in the default clock mode,
10. Use clock mode 11 with SCLK up to 4.8MHz for
externally timed acquisitions to achieve sampling rates
up to 300ksps. Clock mode 11 disables scanning and
averaging. See Figures 6–9 for timing specifications on
how to begin a conversion.
These devices feature an active-low, end-of-conversion
output. EOC goes low when the ADC completes the
last requested operation and is waiting for the next
command byte. EOC goes high when CS or CNVST go
low. EOC is always high in clock mode 11.
The MAX1220–MAX1223/MAX1257/MAX1258 use a
fully differential ADC for all conversions. When a pair of
inputs are connected as a differential pair, each input is
connected to the ADC. When configured in single-
ended mode, the positive input is the single-ended
channel and the negative input is referred to AGND.
See Figure 2.
In differential mode, the T/H samples the difference
between two analog inputs, eliminating common-mode
DC offsets and noise. IN+ and IN- are selected from
the following pairs: AIN0/AIN1, AIN2/AIN3, AIN4/AIN5,
AIN6/AIN7, AIN8/AIN9, AIN10/AIN11, AIN12/AIN13,
1
0
0
0
0
0
REFSEL1
CHSEL0
NAVG1
BIT 3
Single-Ended or Differential Conversions
X
1
0
0
0
0
REFSEL0
SCAN1
NAVG0
RESET
BIT 2
X
0
0
0
0
DIFFSEL1
NSCAN1
SCAN0
SLOW
BIT 1
X
1
1
0
0
DIFFSEL0
NSCAN0
FBGON
TEMP
BIT 0
X
1
0
1
0