8.8 Power-Up Sequence
The ADC resets to the ADC off state. Before writing to any of the ADC registers the ADCENCLK bit in the
PCLKCR0 register must be set. For a description of the PCLKCR0 register, see the System Control and
Interrupts section in this manual. When powering up the ADC, use the following sequence:
1. If an external reference is desired, enable this mode using bit 3 (ADCREFSEL) in the ADCCTL1 register.
2. Power up the reference, bandgap, and analog circuits together by setting bits 7-5 (ADCPWDN,
ADCBGPWD, ADCREFPWD) in the ADCCTL1 register.
3. Enable the ADC by setting bit 14 (ADCENABLE) of the ADCCTL1 register.
4. Before performing the first conversion, a delay of 1 millisecond after step 2 is required.
Alternatively, steps 1 through 3 can be performed simultaneously.
When powering down the ADC, all three bits in step 2 can be cleared simultaneously. The ADC power levels
must be controlled via software and they are independent of the state of the device power modes.
Note
This type ADC requires a 1ms delay after all of the circuits are powered up. This differs from the
previous type ADC's.
8.9 ADC Calibration
Inherent in any converter is a zero offset error and a full scale gain error. The ADC is factory calibrated at
30-degrees Celsius to correct both of these while allowing the user to modify the offset correction for any
application environmental effects, such as the ambient temperature. Except under certain emulation conditions,
or unless a modification from the factory settings is desired, the user is not required to perform any specific
action. The ADC will be properly calibrated during the device boot process.
Note
If the system is reset or the ADC module is reset using Bit 15 (RESET) from the ADC Control Register
1, the Device_cal() routine must be repeated.
8.9.1 Factory Settings and Calibration Function
During the fabrication and test process Texas Instruments calibrates several ADC settings along with a couple
of internal oscillator settings. These settings are embedded into the TI reserved OTP memory as part of a
C-callable function named Device_cal(). Called during the startup boot procedure in the Boot ROM this function
writes the factory settings into their respective active registers. Until this occurs, the ADC and the internal
oscillators will not adhere to their specified parameters. If the boot process is skipped during emulation, the
user must ensure the trim settings are written to their respective registers to ensure the ADC and the internal
oscillators meet the specifications in the data sheet. This can be done either by calling this function manually or
in the application itself, or by a direct write via CCS. A gel function for device calibration is included in CCS when
the appropriate .ccxml file is created for the target MCU.
For more information on the Device_cal() function refer to the Boot ROM section in this manual.
Texas Instruments cannot assure the parameters specified in the data sheet, if a value other than the factory
settings contained in the TI reserved OTP memory is written into the ADC trim registers.
8.9.2 ADC Zero Offset Calibration
Zero offset error is defined as the resultant digital value that occurs when converting a voltage at VREFLO. This
base error affects all conversions of the ADC and together with the full scale gain and linearity specifications,
determine the DC accuracy of a converter. The zero offset error can be positive, meaning that a positive digital
value is output when VREFLO is presented, or negative, meaning that a voltage higher than a one step above
VREFLO still reads as a digital zero value. To correct this error, the two's complement of the error is written into
the ADCOFFTRIM register. The value contained in this register will be applied before the results are available
in the ADC result registers. This operation is fully contained within the ADC core, so the timing for the results
Analog-to-Digital Converter (ADC)
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
TMS320x2806x Microcontrollers
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Содержание TMS320 2806 Series
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