Datasheet
0.1 F(typ)m
VDD
5
10
1
2
3
4
SCLK
CS
GND
AIN0
AIN1
DIN
9
8
7
6
DOUT/DRDY
VDD
AIN3
AIN2
Device
InputsSelected
fromConfiguration
Register
ADS1018
SBAS526B –NOVEMBER 2012–REVISED OCTOBER 2013
www.ti.com
USING GPIO PORTS FOR COMMUNICATION
Most microcontrollers have programmable input/output (I/O) pins that can be set in software to act as inputs or
outputs. If an SPI controller is not available, the ADS1018 can be connected to GPIO pins and the SPI bus
protocol can be simulated. Using GPIO pins to generate the SPI interface only requires that the pins be
configured as push or pull inputs or outputs. Furthermore, if the SCLK line is held low for more than 28 ms, the
communication times out. This condition means that the GPIO ports must be capable of providing SCLK pulses
with no more than 28 ms between pulses.
SINGLE-ENDED INPUTS
Although the ADS1018 has two differential inputs, the device can easily measure four single-ended signals.
Figure 21 shows a single-ended connection scheme. The ADS1018 is configured for single-ended measurement
by configuring the MUX to measure each channel with respect to ground. Data are then read out of one input
based on the selection in the Config register. The single-ended signal can range from 0 V up to positive supply
or +FS, whichever is lower. Negative voltages cannot be applied to this circuit because the ADS1018 can only
accept positive voltages with respect to ground. The ADS1018 does not loose linearity within the input range.
The ADS1018 offers a differential input voltage range of ±FS. The single-ended circuit shown in Figure 21
however only uses the positive half of the ADS1018 FS input voltage range because it does not produce
differentially negative inputs. Because only half of the FS range is used, one bit of resolution is lost. For optimal
noise performance, TI recommends using differential configurations whenever possible. Differential
configurations maximize the dynamic range of the ADC and provide strong attenuation of common-mode noise.
NOTE: Digital pin connections omitted for clarity.
Figure 21. Measuring Single-Ended Inputs
The ADS1018 is also designed to allow AIN3 to serve as a common point for measurements by adjusting the
MUX configuration. AIN0, AIN1, and AIN2 can all be measured with respect to AIN3. In this configuration the
ADS1018 can operate with inputs where AIN3 serves as the common point. This ability improves the usable
range over the single-ended configuration because it allows negative differential voltages when GND < AIN3 <
VDD; however, it does not offer attenuation of common-mode noise.
24 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated
Product Folder Links: ADS1018