MC9S08GB60A Datasheet, PDF (227/302 Pages) Freescale Semiconductor, Inc – HCS08 Microcontrollers

Analog-to-Digital Converter (S08ATDV3)
Table 14-1. Signal Properties
Name
AD7–AD0
V_REFH
V_REFL
V_DDAD
V_SSAD
Function
Channel input pins
High reference voltage for ATD converter
Low reference voltage for ATD converter
ATD power supply voltage
ATD ground supply voltage
14.2.1.1 Channel Input Pins — AD1P7–AD1P0
The channel pins are used as the analog input pins of the ATD. Each pin is connected to an analog switch
which serves as the signal gate into the sample submodule.
14.2.1.2 ATD Reference Pins — V_REFH, V_REFL
These pins serve as the source for the high and low reference potentials for the converter. Separation from
the power supply pins accommodates the filtering necessary to achieve the accuracy of which the system
is capable.
14.2.1.3 ATD Supply Pins — V_DDAD, V_SSAD
These two pins are used to supply power and ground to the analog section of the ATD. Dedicated power
is required to isolate the sensitive analog circuitry from the normal levels of noise present on digital power
supplies.
NOTE
V_DDAD1 and V_DD must be at the same potential. Likewise, V_SSAD1 and V_SS
must be at the same potential.
14.3 Functional Description
The ATD uses a successive approximation register (SAR) architecture. The ATD contains all the necessary
elements to perform a single analog-to-digital conversion.
A write to the ATD1SC register initiates a new conversion. A write to the ATD1C register will interrupt
the current conversion but it will not initiate a new conversion. A write to the ATD1PE register will also
abort the current conversion but will not initiate a new conversion. If a conversion is already running when
a write to the ATD1SC register is made, it will be aborted and a new one will be started.
14.3.1 Mode Control
The ATD has a mode control unit to communicate with the sample and hold (S/H) machine and the SAR
machine when necessary to collect samples and perform conversions. The mode control unit signals the
S/H machine to begin collecting a sample and for the SAR machine to begin receiving a sample. At the
end of the sample period, the S/H machine signals the SAR machine to begin the analog-to-digital
conversion process. The conversion process is terminated when the SAR machine signals the end of
MC9S08GB60A Data Sheet, Rev. 2
Freescale Semiconductor
227