Maxim Integrated 6-8
MAX31782 User’s Guide
Revision 0; 8/11
6.2.4 ADC Data and Configuration Register (ADDATA)
Register Address: M2[09h]
The ADDATA register is used to set up the ADC sequence configurations and also to read the results of the ADC con-
versions. If the ADST.ADCFG bit is set to 1, writing to ADDATA writes to one of the configuration registers. If ADST.
ADCFG is set to 0, reading from ADDATA reads one of the conversion results.
6.2.4.1 ADC Configuration Register (ADDATA when ADCFG = 1)
When ADCFG = 1, writing to the ADDATA register writes to one of the configuration registers. The configuration register
written to is selected by the ADIDX[2:0] bits. The ADIDX[2:0] bits automatically increment after a write to ADDATA. This
allows consecutive writes of ADDATA to set up consecutive configuration registers. The configuration registers are reset
to 0 on all forms of reset and are not writable by the user.
*When ADCFG = 1, unrestricted read, but can only be written to when ADCONV = 0.
Bit
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Name — — — — — — — — EXTEMP ADGAIN ADACQEN ADALIGN ADDIFF ADCH2 ADCH1 ADCH0
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Access r r r r r r r r rw* rw* rw* rw* rw* rw* rw* rw*
BIT NAME DESCRIPTION
15:8 —
Reserved. The user should not write to these bits.
7 EXTEMP
External Temperature Mode: Setting this bit to one chooses external temperature sensing operation.
If this bit is set to zero, the ADC operates in normal voltage conversion mode for ADCH = 0–5. For
ADCH = 6 or 7, the internal temperature is measured regardless of the setting of this bit. For external
temperature measurement, the ADC does the following:
• A current source generated on the chip is directed to one of six positive ADC channel pins
(AD0P–AD5P) based on channel select bits described in the configuration section.
• The current passing through the external diode is expected to return on the negative input pins
(AD0N–AD5N) of the corresponding channel.
• The voltage across the positive and negative inputs of the channel is then scaled appropriately to
produce a temperature sample with a slope of 2.4mV/NC.
• The internal reference is chosen during both temperature measurement modes, external and
internal, regardless of IREFEN bit value.
• The slope of the temperature can additionally be controlled by up to +2% in increments of ~0.25NC
to accommodate the variance in ideality factor of the diode being used. The slope comes
preprogrammed with a 2N3904 used as a reference. The control register is at ETS (M1[16]) SFR.
• The slope of the internal temperature sensor is not user adjustable and set at the factory.
• The measured temperature is reported in the ADDATA register.
6 ADGAIN
ADC Reference Select. This bit selects the ADC scale factor.
IREFEN ADGAIN ADCSCALE
1 0 ADCG1
1 1 ADCG5
0 X ADCG1
5 ADACQEN
ADC Acquisition Extension Enable. Setting this bit to 1 enables additional acquisition time to be insert-
ed prior to this conversion. Clearing this bit to 0 disables the extended acquisition time.
4 ADALIGN
ADC Data Alignment Select. This bit selects the ADC data alignment mode. Setting this bit to 1
returns ADC data left-aligned in ADDATA [15:3] with ADDATA[2:0] zero padded. Clearing this bit to
0 returns ADC data in right-aligned format in ADDATA[12:0] with ADDATA[15:13] sign-extended by
ADDATA[12].
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