6.2 Laboratory signal acquisition: lab3 - sd16_a adc conversion  (Page 9/2)

Laboratory signal acquisition: lab3 - sd16_a adc conversion

Introduction

This laboratory gives examples of the uses of the ADC types available in the hardware development kits. A different laboratory is developed for each kit, taking into account that both the ADC10 and the SD16_A laboratories implement a temperature data logger. The ADC12 laboratory also uses operational amplifiers to perform the analogue signal conditioning.

Overview

This laboratory ( Lab3_ADC.c ) implements a temperature data logger using the hardware kit’s integrated temperature sensor. The device is configured to perform a data acquisition once every minute for one hour. Each temperature’s (ºC) value is transferred to flash info memory segment B and C. When the microcontroller is not performing any task, it enters into low power mode.

Resources

The SD16_A module uses V _REF+ = 1.2 V as reference voltage.

It is necessary to select the channel 6 of the SD16_A to use the integrated temperature sensor as an input. Timer_A generates an interrupt once every second, which starts conversion on the SD16_A. At the end of conversion, an interrupt is requested by the converter and the temperature value is written to flash memory.

The voltage value is converted into temperature using the mathematical expression provided in the eZ430-F2013 data sheet. After transferring the value to the flash memory, the system returns to low power mode LPM3.

The resources used by the application are:

- SD16_A;

- Timer_A;

- Ports I/O;

- Interrupts;

- Low power mode.

Software application organization

The application starts by stopping the Watchdog Timer.

System tests for the presence of calibration constants in info memory segment A. The CPU execution will be trapped if it does not find this information.

The digital controller oscillator (DCO) is set to 1 MHz to provide clock sources for MCLK and SMCLK, while the Basic Clock System+ is configured to set ACLK to 1.5 kHz.

The controller’s flash timing is obtained from MCLK, divided by three to comply with the device specifications.

Port P1.0 is configured as output and will blink the LED once every second.

The SD16_A is configured to use the input channel corresponding to the on-chip temperature sensor (channel A6). The configuration includes the activation of the internal reference voltage: V _REF+ = 1.2 V and the selection of SMCLK as clock signal. The converter is configured to perform a single conversion in bipolar mode and offset binary format. At the end of conversion an interrupt is requested.

The Timer_A is configured to generate an interrupt once every second. ACLK/8 is selected as the clock signal using VLOCLK as clock source and will count until it reaches the TACCR0 value (up mode). The system enters into low power mode and waits for an interrupt.

Flash memory pointers and interrupt counters are initialized. The Timer_A ISR increments variable counter and when this variable reaches the value 60 (1 minute), the software start of conversion is requested. At the end of this ISR, the system returns to low power mode.