HCS08 datasheet(135/374 Pages) NXP

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Chapter 10 Analog-to-Digital Converter (S08ADC12V1)

MC9S08JM60 Series Data Sheet, Rev. 5

Freescale Semiconductor

135

ADCSC2[ADTRG] bit. When enabled, the ADC will be triggered every time RTCINT matches

RTCMOD. The RTC interrupt does not have to be enabled to trigger the ADC.

The RTC can be configured to cause a hardware trigger in MCU run, wait, and stop3.

10.1.1.4

Analog Pin Enables

The ADC on MC9S08JM60 series contains only two analog pin enable registers, APCTL1 and APCTL2.

10.1.1.5

Temperature Sensor

The ADC module includes a temperature sensor whose output is connected to one of the ADC analog

channel inputs. Equation 10-1 provides an approximate transfer function of the temperature sensor.

Temp = 25 – ((VTEMP – VTEMP25) ÷ m)

Eqn. 10-1

where:

—VTEMP is the voltage of the temperature sensor channel at the ambient temperature.

—VTEMP25 is the voltage of the temperature sensor channel at 25°C.

— m is the hot or cold voltage versus temperature slope in V/

°C.

For temperature calculations, use the VTEMP25 and m values from the ADC Electricals table.

In application code, the user reads the temperature sensor channel, calculates VTEMP, and compares to

VTEMP25. If VTEMP is greater than VTEMP25, the cold slope value is applied in Equation 10-1. If VTEMP

is less than VTEMP25 the hot slope value is applied in Equation 10-1.

To improve accuracy, calibrate the bandgap voltage reference and temperature sensor. Calibrating at

°C will improve accuracy to ±4.5°C. Calibration at 3 points, –40°C, 25°C, and 125°C will improve

accuracy to ±2.5

°C. Once calibration has been completed, the user will need to calculate the slope for both

hot and cold. In application code, the user would then calculate the temperature using Equation 10-1 as

detailed above and then determine if the temperature is above or below 25

°C. Once determined, if the

temperature is above or below 25

°C, the user can recalculate the temperature using the hot or cold slope

value obtained during calibration.

10.1.2

Low-Power Mode Operation

The ADC is capable of running in stop3 mode but requires LVDSE and LVDE in SPMSC1 to be set.

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