Analog-to-Digital Converter (ADC)
MCF52110 ColdFire® Integrated Microcontroller Reference Manual, Rev. 1
25-26
Freescale Semiconductor
Preliminary
25.5.2.1
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
.
25.5.2.2
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
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
V
IN
V
REFL
–
V
REFH
V
REFL
–
-----------------------------------------
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
V
IN
1
V
IN
2
–
V
REFH
V
REF LO
–
-------------------------------------------
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.
