Datasheet

MC68HC908QB8 Data Sheet, Rev. 3
Freescale Semiconductor 37
Chapter 3
Analog-to-Digital Converter (ADC10) Module
3.1 Introduction
This section describes the 10-bit successive approximation analog-to-digital converter (ADC10).
The ADC10 module shares its pins with general-purpose input/output (I/O) port pins. See Figure 3-1 for
port location of these shared pins. The ADC10 on this MCU uses V
DD
and V
SS
as its supply and reference
pins. This MCU uses BUSCLKX4 as its alternate clock source for the ADC. This MCU does not have a
hardware conversion trigger.
3.2 Features
Features of the ADC10 module include:
• Linear successive approximation algorithm with 10-bit resolution
• Output formatted in 10- or 8-bit right-justified format
• Single or continuous conversion (automatic power-down in single conversion mode)
• Configurable sample time and conversion speed (to save power)
• Conversion complete flag and interrupt
• Input clock selectable from up to three sources
• Operation in wait and stop modes for lower noise operation
• Selectable asynchronous hardware conversion trigger
3.3 Functional Description
The ADC10 uses successive approximation to convert the input sample taken from ADVIN to a digital
representation. The approximation is taken and then rounded to the nearest 10- or 8-bit value to provide
greater accuracy and to provide a more robust mechanism for achieving the ideal code-transition voltage.
Figure 3-2 shows a block diagram of the ADC10
For proper conversion, the voltage on ADVIN must fall between V
REFH
and V
REFL
. If ADVIN is equal to
or exceeds V
REFH
, the converter circuit converts the signal to $3FF for a 10-bit representation or $FF for
a 8-bit representation. If ADVIN is equal to or less than V
REFL
, the converter circuit converts it to $000.
Input voltages between V
REFH
and V
REFL
are straight-line linear conversions.
NOTE
Input voltage must not exceed the analog supply voltages.