User's Manual

System Overview and Functional Block Descriptions
1322x Sensor Node Reference Manual, Rev. 1.1
Freescale Semiconductor 3-5
3.7 Debug/Development Interface
There is a standard JTAG debug port (for pinouts see Section 4.6, “Debug/Development Connector (ARM
JTAG Interface)”). A 20-pin connector is provided for a standard JTAG debug interface that only requires
a simple interface cable to connect to the PC and uses standard ARM software development tools.
3.8 Sensors
The SN provides a temperature sensor, a pressure sensor, and a three axis low-g accelerometer. All three
sensors provide analog voltage outputs and require use of the MC13224/225 ADCs.
NOTE
• There are two VREFH voltages. ADC2_VREFH is tied to the device
VCC and moves with the VCC voltage, i.e., either the regulated voltage
or the battery voltage. ADC2_VREFH is useful if the application wants
the ADC reference to scale with the supply voltage (as for audio),
however, it is unreliable for a fixed voltage reference such as the
temperature sensor. In contrast, ADC1_VREFH is tied to a fixed 1.5 V
reference (see Section 4.10, “ADC Voltage References”). This fixed
reference should be used for battery operation where a known voltage is
required.
• All sensor voltage outputs are conditioned with RC filtering to help
eliminate noise.
• The user is referenced to the individual data sheets for each of the
sensors for detailed information.
3.8.1 Temperature Sensor
The temperature sensor is a National Semiconductor LM61BIM3. Its accuracy is ±3°C, and its output
voltage is typically 0.600 Vdc at 0°C with a slope of +10 mV/°C. The sensor requires only one ADC input
and is constantly powered.
Figure 3-5. Typical Voltage Out vs. Temperature for LM61B
0.000
0.200
0.400
0.600
0.800
1.000
1.200
0 102030405060
Temp (Degrees C)
Temp Vo (Vdc)