Datasheet

Chapter 10 Analog-to-Digital Converter (S08ADC12V1)
MC9S08JM16 Series Data Sheet, Rev. 2
134 Freescale Semiconductor
NOTE
Selecting the internal bandgap channel requires BGBE =1 in SPMSC1, see
Section 5.7.7, “System Power Management Status and Control 1 Register
(SPMSC1).” For value of bandgap voltage reference see Appendix A.8,
“Analog Comparator (ACMP) Electricals.”
10.1.1.2 Alternate Clock
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
ALTCLK on this device is MCGERCLK.
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
ADCK
) after being divided down from the ALTCLK input as
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 stop3.
10.1.1.3 Hardware Trigger
The RTC on this device can be enabled as a hardware trigger for the ADC module by setting the
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 MC9S08JM16 series contain 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 – ((V
TEMP
– V
TEMP25
) ÷ m) Eqn. 10-1
where:
—V
TEMP
is the voltage of the temperature sensor channel at the ambient temperature.
01111 AD15 V
REFL
ADPC15 11111 module
disabled
None N/A
1
For more information, see Section 10.1.1.5, “Temperature Sensor.”
Table 10-1. ADC Channel Assignment (continued)
ADCH Channel Input Pin Control ADCH Channel Input Pin Control