LM3S317 Luminary Micro, Inc, LM3S317 Datasheet - Page 302

• Manufacturer Part Number: LM3S317
• Description: Lm3s317 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

Analog Comparator
14.3
302
Figure 14-3. Comparator Internal Reference Structure
Table 14-2. Internal Reference Voltage and ACREFCTL Field Values
Initialization and Configuration
The following example shows how to configure analog comparator to read back its output value
from an internal register.
1.
2.
3.
4.
EN Bit Value
Enable the analog comparator 0 clock by writing a value of 0x00100000 to the RCGC1 register
in the System Control module.
In the GPIO module, enable the GPIO port/pin associated with C0- as a GPIO input.
Configure the internal voltage reference to 1.65 V by writing the ACREFCTL register with the
value 0x0000030C.
Configure comparator 0 to use the internal voltage reference and to not output a value on the
C0O pin by writing the ACCTL0 register with the value of 0x0000040C.
EN=0
EN=1
ACREFCTL Register
VREF
RNG
EN
RNG Bit Value
RNG=X
RNG=0
RNG=1
AVDD
8R
Preliminary
0 V (GND) for any value of VREF; however, it is recommended that
RNG=1 and VREF=0 for the least noisy ground reference.
Total resistance in ladder is 32 R.
The range of internal reference in this mode is 0.825–2.37 V.
Total resistance in ladder is 24 R.
The range of internal reference for this mode is 0.0–2.0625 V.
R
Output Reference Voltage Based on VREF Field Value
15
R
14
•••
Decoder
•••
V
V
R
REF
REF
V
V
V
V
REF
REF
REF
REF
=
1
=
R
=
0.825
AV
=
=
=
AV
AV
AV
0.1375 VREF
DD
0
DD
+
DD
DD
×
0.103 VREF
8R
(
-----------------------------
×
×
×
VREF
⋅
(
------------------- -
R
--------------- -
R
--------------- -
VREF
VREF
VREF
R
R
32
24
⋅
T
T
+
)
8
internal
reference
)
February 6, 2007