9.5 Basic Operation of the ADC10

We now look at some simple examples of measurements using the basic hardware of the ADC10. More complicated aspects, such as triggering from hardware and the data transfer controller, are covered in the following section.

Three steps are required to make a single conversion with the ADC10. I assume that the default references of V _SS and V _CC are suitable so that we need not worry about the settling time of the reference or buffer.

1. Configure the ADC10, including the ADC10ON bit to enable the module. The ENC bit must be clear during this operation because most bits in ADC10CTL0 and ADC10CTL1 can be changed only when ENC = 0.

2. Set the ENC bit to enable a conversion. This cannot be done while the module is being configured in the previous step.

3. Trigger the conversion, either by setting the ADC10SC bit or by an edge from Timer_A.

The last two steps must be repeated for each conversion, which requires clearing and setting the ENC bit again. This might seem a bit cumbersome if you have used an ADC in another microcontroller, where these steps are typically combined. The reason for enforcing two steps is that the ADC10 can be triggered directly from Timer_A, not just from software. A new conversion should not start until the old one has been processed and conversions reenabled by toggling ENC. (It is the same as using the "single sequence" button on a digital storage oscilloscope.)