mc9s08sg4 Freescale Semiconductor, Inc, mc9s08sg4 Datasheet - Page 118

• Manufacturer Part Number: mc9s08sg4
• Description: 8-bit Microcontroller Family
• Manufacturer: Freescale Semiconductor, Inc

Chapter 9 Analog-to-Digital Converter (S08ADCV1)
9.1.2
The ADC module is capable of performing conversions using the MCU bus clock, the bus clock divided
by two, the local asynchronous clock (ADACK) within the module, or the alternate clock, ALTCLK. The
alternate clock for the MC9S08SG8 MCU devices is the external reference clock (ICSERCLK).
The selected clock source must run at a frequency such that the ADC conversion clock (ADCK) runs at a
frequency within its specified range (f
determined by the ADIV bits.
ALTCLK is active while the MCU is in wait mode provided the conditions described above are met. This
allows ALTCLK to be used as the conversion clock source for the ADC while the MCU is in wait mode.
ALTCLK cannot be used as the ADC conversion clock source while the MCU is in either stop2 or stop3.
9.1.3
The ADC hardware trigger, ADHWT, is the output from the real time counter (RTC). The RTC counter
can be clocked by either ICSERCLK, ICSIRCLK or a nominal 1 kHz clock source.
The period of the RTC is determined by the input clock frequency, the RTCPS bits, and the RTCMOD
register. When the ADC hardware trigger is enabled, a conversion is initiated upon an RTC counter
overflow. The RTIE does not have to be set for RTC to cause a hardware trigger.
The RTC can be configured to cause a hardware trigger in MCU run, wait, and stop3.
9.1.4
To use the on-chip temperature sensor, the user must perform the following:
Equation 9-1
Temp = 25°C, using the ADC1 at f
0.0017 is the uncalibrated voltage versus temperature slope in V/°C. Uncalibrated accuracy of the
temperature sensor is approximately
To improve accuracy the user should calibrate the bandgap voltage reference and temperature sensor.
Calibrating at 25°C will improve accuracy to
118
•
•
•
Configure ADC for long sample with a maximum of 1 MHz clock
Convert the bandgap voltage reference channel (AD27)
— By converting the digital value of the bandgap voltage reference channel using the value of
Convert the temperature sensor channel (AD26)
— By using the calculated value of V
V
Characteristics”.
Alternate Clock
Hardware Trigger
Temperature Sensor
BG
provides an approximate transfer function of the on-chip temperature sensor for V
the user can determine V
Temp
MC9S08SG8 MCU Series Data Sheet, Rev. 3
C
ADCK
= 25 - ( (V
±
ADCK
12°C, using
= 1.0MHz and configured for long sample.
DD
) after being divided down from the ALTCLK input as
. For value of bandgap voltage, see
TEMP
±
DD
4.5°C.
, convert the digital value of AD26 into a voltage,
- 0.7013) / 0.0017 )
Equation
9-1.
Section A.6, “DC
Freescale Semiconductor
DD
Eqn. 9-1
= 5.0V,
V
TEMP