MC9S08QG8 Datasheet, PDF (116/300 Pages) Freescale Semiconductor, Inc – 8-BIT HCS08 Central Processor Unit

Chapter 9 Analog-to-Digital Converter (S08ADC10V1)
9.1.1.3 Alternate Clock
The ADC is capable of performing conversions using the MCU bus clock, the bus clock divided by two,
or the local asynchronous clock (ADACK) within the module. The alternate clock, ALTCLK, input for the
MC9S08QG8/4 MCU devices is not implemented.
9.1.1.4 Hardware Trigger
The ADC hardware trigger, ADHWT, is output from the real-time interrupt (RTI) counter. The RTI counter
can be clocked by either ICSERCLK or a nominal 1-kHz clock source within the RTI block.
The period of the RTI is determined by the input clock frequency and the RTIS bits. The RTI counter is a
free running counter that generates an overflow at the RTI rate determined by the RTIS bits. When the ADC
hardware trigger is enabled, a conversion is initiated upon a RTI counter overflow.
The RTI can be configured to cause a hardware trigger in MCU run, wait, and stop3.
9.1.1.5 Analog Pin Enables
The ADC on MC9S08QG8 contains only one analog pin enable register, APCTL1.
9.1.1.6 Temperature Sensor
The ADC module includes a temperature sensor whose output is connected to one of the ADC analog
channel inputs. Equation 9-1 provides an approximate transfer function of the temperature sensor.
Temp = 25 - ((V_TEMP -V_TEMP25) ÷ m)
Eqn. 9-1
where:
— V_TEMP is the voltage of the temperature sensor channel at the ambient temperature.
— V_TEMP25 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 V_TEMP25 and m values from Section A.10, “ADC Characteristics,”
in Appendix A, “Electrical Characteristics.”
In application code, the user reads the temperature sensor channel, calculates V_TEMP, and compares to
V_TEMP25. If V_TEMP is greater than V_TEMP25 the cold slope value is applied in Equation 9-1. If V_TEMP is
less than V_TEMP25 the hot slope value is applied in Equation 9-1.
For more information on using the temperature sensor, consult Freescale document AN3031.
9.1.1.7 Low-Power Mode Operation
The ADC is capable of running in stop3 mode but requires LVDSE and LVDE in SPMSC1 to be set.
MC9S08QG8 and MC9S08QG4 Data Sheet, Rev. 1.01
116
Freescale Semiconductor