2 Firmware Implementation

One benefit of this design is that firmware does not need to be programmed into the device. This design utilizes the ROM functions inside of the RF430FRL152H. The device is initialized “over the air” by a NFC/RFID Reader/Writer device that writes the configuration registers. Subsequently, the thermistor measurements are read out by this same Reader/Writer device. When utilizing the graphical user interface (GUI) software as discussed in Section 3, the RF430FRL152H will be configured as shown below. It is important to note that with this specific configuration, each sample requires 128 ms for acquisition. The reference resistor and thermistor must be sampled for each measurement, which brings the total conversion time to 256 ms. This is just one implementation of the ADC configuration register that can be modified to meet the needs of a given application.

• Sensor Control Register
  The Sensor Control Register is used to select the thermistor to be sampled. The reference resistor (R3) is also sampled and used for Calibration.
  • Reference/ADC1 Sensor enabled
  • Thermistor/ADC2 Sensor enabled
  • Thermistor enabled, number of passes = 1
• Reference/ADC1 Sensor Configuration Register
  This register is used to configure the ADC1 for the reference resistor. The configuration below sets the ADC for 10-bit resolution and requires 128 ms for each sample. In this application example, 10-bit resolution was used for this for faster conversions.
  • Gain = 2
  • Filter Type = CIC Filter
  • Oversampling = 128
• Thermistor/ADC2 Sensor Configuration Register
  This register is used to configure the ADC1 for the Thermistor. The configuration below sets the ADC for 10-bit accuracy and requires 128 ms for each sample. In this application example, 10-bit resolution was used for this for faster conversions.
  • Gain = 2
  • Filter Type = CIC Filter
  • Oversampling = 128

NOTE

The configuration of the device can also be read out using the RF430FRL152H GUI “Read All Tabs” button and viewing the tabs that contain the affected registers.