Texas Instruments MSP430x1xx - Manual (Page 293)

Introduction
15-3
ADC12
The ADC12 has versatile sample-and-hold circuitry giving the user many
options for control of the sample timing. The sample timing may be directly
controlled by software (via a control bit), or any one of three internal or external
signals (depending on device configuration – see
Sampling section and check
the data sheet for details). Typically, the internal timing signals come from
other MSP430 timers such as Timer_A. Additionally, the sample timing may
be programmed as a multiple of the ADC12 conversion clock.
As with sample timing, the user has several choices for the ADC12 conversion
clock. The ADC12 conversion clock may be chosen from any available internal
MSP430 clock, or may be selected from a dedicated oscillator contained in the
ADC12 peripheral. Additionally, the chosen clock source may be divided by
any factor from 1 to 8.
The ADC12 has four operating modes. It can be configured to perform a single
conversion on a single channel, or multiple conversions on a single channel.
The ADC12 can also be configured to perform conversions on a sequence-of-
channels, running through the sequence once, or repeatedly. When
performing conversions on a sequence-of-channels, the sequence is
completely definable by the user. For example, a possible sequence-of-
channels could be a1–a3–a1–a6–a2, etc. In addition, each channel may be
individually configured for which reference(s) are to be used for the
conversion.
Conversion results are stored in 16 conversion-memory registers. Each of
these registers has its own configuration and control register allowing the user
to select the input channel and the reference(s) used for the conversion result
that is stored in that register.
Some key and unique features of the ADC12 are:
- 200-ksps maximum conversion rate
- 12-bit converter with
±
1LSB differential nonlinearity (DNL) and
±
1LSB in-
tegral nonlinearity (INL)
- Built-in sample-and-hold with selectable sampling periods controlled by
software (via a control bit), a sampling timer, or by other MSP430 timers
- On-chip, dedicated RC oscillator – used as an option for sample-and-
conversion timing
- Integrated diode for temperature measurement
- Eight individually configurable channels for conversion of external signals
- Four internal channels for conversion of temperature, AV
cc
, and external
references
- On-chip reference voltages – 1.5 V or 2.5 V, selected by software
- Selectable internal or external sources for both positive and negative
reference-voltage levels (selectable for each channel independently)
- Selectable conversion clock source