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Analog-to-Digital Converter (ADC)
MCF52211 ColdFire® Integrated Microcontroller Reference Manual, Rev. 2
26-26 Freescale Semiconductor
26.5.2.1 Single-Ended Samples
The ADC module performs a ratio metric conversion. For single ended measurements, the digital result is
proportional to the ratio of the analog input to the reference voltage in the following formula:
Single-ended measurements return the max value 32760 when the input is at V
REFH
, return 0 when the
input is at V
REFL
, and scale linearly between based on the amount by which the input exceeds V
REFL
.
26.5.2.2 Differential Samples
For differential measurements, the digital result is proportional to the ratio of the difference in the inputs
to the difference in the reference voltages (V
REFH
and V
REFL
). Figure 26-22 shows typical configurations
for differential inputs.
When converting differential measurements, the following formula is useful:
Differential measurements return the max value 32760 (= 4095 × 8) when the plus (+) input is V
REFH
and
the minus (−) input is V
REFL
, return 0 when the plus (+) input is at V
REFL
and the minus (−) input is at
V
REFL
, and scale linearly between based on the voltage difference between the two signals.
SingleEndedValue round
VIN VREFL–
V
REFH VREFL–
-----------------------------------------
4095×()8×=
VIN = Applied voltage at the input pin
VREFH and VREFL = Voltage at the external reference pins on the device (typically VREFH = VSSA and
VREFL = VDDA)
Note: The 12-bit result is rounded to the nearest LSB.
Note: The ADC is a 12-bit function with 4096 possible states. However, the 12 bits have been left
shifted three bits on the 16-bit data bus so its magnitude, as read from the data bus, is now
32760.
DifferentialValue round
VIN1VIN2–
V
REFH VREFLO–
-------------------------------------------
4095×()8×=
V
IN
= Applied voltage at the input pin
V
REFH
and V
REFL
= Voltage at the external reference pins on the device (typically V
REFH
= V
SSA
and V
REFL
=
V
DDA
)
Note: The 12-bit result is rounded to the nearest LSB.
Note: The ADC is a 12-bit function with 4096 possible states. However, the 12 bits have been left
shifted three bits on the 16-bit data bus so its magnitude, as read from the data bus, is now
32760.