Analog to Digital (ATD) Module
MC1321x Reference Manual, Rev. 1.6
Freescale Semiconductor
20-3
20.2
Signal Description
20.2.1
Overview
The ATD supports eight input channels and requires 4 supply/reference/ground pins. These pins are listed
in
20.2.1.1
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 sub module.
20.2.1.2
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.
20.2.1.3
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.
20.3
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.
Table 20-1. Signal Properties
Name
Function
AD7–AD0
Channel input pins
V
REFH
High reference voltage for ATD converter
V
REFL
Low reference voltage for ATD converter
V
DDAD
ATD power supply voltage
V
SSAD
ATD ground supply voltage
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