7.1 7.2 - analog-to-digital converter on the msp430

The analog to digital converter (ADC) on the ez430 is a type called a Sigma-Delta (SD) Converter. The way it operates is slightly different from what was described in the previous section (although the end result is the same) but those specifics are out of the scope of this course. The SD converter on the ez430 has 8 channels and a 16 bit resolution. The module is highly configurable and can run largely free of program involvement. In this portion of the lab, we will broadly explain the features of the module, but the particular effects of each register are listed, as usual, in Chapter 12 of the User’s Guide .

Range of measurement

The result of each conversion will be 16 bits long in the form of an unsigned integer whose value is:

Input channels for the adc

The following is a table of the 8 input channels on the ez430. "Analog signal input" channels will take any analog source (we will get to the pin mapping's shortly). Other channels perform specific tool integrated tasks. For example, channel A6 is an integrated temperature sensor. For detailed descriptions of the others, see the User's Guide .

Sd16 input channels

• A0 : Analog signal input
• A1 : Analog signal input
• A2 : Analog signal input
• A3 : Analog signal input
• A4 : Analog signal input
• A5 : $\frac{\mathrm{Vcc}-\mathrm{Vss}}{11}$
• A6 : Integrated temperature sensor
• A7 : Short for PGA offset measurement

Operation reminders for the adc

Remember the following when attempting to use the ADC:

• Be sure to enable SD16 interrupts (on SD16CCTL0 ) and to select the specific channel which you are using (on SD16INCTL )
• After configuring the ADC, you must enable the SD16SC bit to start conversion.
• All ADC values will be stored in the SD16MEMx variable where "x" is the number of the channel