mc9s08gt16a Freescale Semiconductor, Inc, mc9s08gt16a Datasheet - Page 230

• Manufacturer Part Number: mc9s08gt16a
• Description: Hcs08 Microcontrollers 8-bit Microcontroller Family
• Manufacturer: Freescale Semiconductor, Inc

Analog-to-Digital Converter (S08ATDV3)
14.4
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 ATDSC register initiates a new conversion. A write to the ATDC register will interrupt the
current conversion but it will not initiate a new conversion. A write to the ATDPE 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 ATDSC register is made, it will be aborted and a new one will be started.
14.4.1
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
conversion to the mode control unit. For V
to set the sampled signal level within itself without relying on the S/H machine to deliver them.
The mode control unit organizes the conversion, specifies the input sample channel, and moves the digital
output data from the SAR register to the result register. The result register consists of a dual-port register.
The SAR register writes data into the register through one port while the module data bus reads data out
of the register through the other port.
14.4.2
The S/H machine accepts analog signals and stores them as capacitor charge on a storage node located in
the SAR machine. Only one sample can be held at a time so the S/H machine and the SAR machine can
not run concurrently even though they are independent machines.
various resistors and capacitors.
230
Functional Description
Mode Control
Sample and Hold
V
AIN
+
–
Figure 14-10. Resistor and Capacitor Placement
R
AS
MC9S08GT16A/GT8A Data Sheet, Rev. 1
C
AS
REFL
INPUT PIN
INPUT PIN
INPUT PIN
INPUT PIN
and V
R
R
R
R
REFH
AIN1
AIN2
AIN3
AINn
.
.
.
CHANNEL
SELECT 0
CHANNEL
SELECT 1
CHANNEL
SELECT 2
CHANNEL
SELECT n
, the SAR machine uses the reference potentials
Figure 14-10
C
AIN
ATD SAR
ENGINE
shows the placement of the
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