LM3S101-CRN20-XNPT Luminary Micro, Inc., LM3S101-CRN20-XNPT Datasheet - Page 253

• Manufacturer Part Number: LM3S101-CRN20-XNPT
• Description: Microcontroller
• Manufacturer: Luminary Micro, Inc.

Analog Comparators
13.2.1
253
Internal Reference Programming
The structure of the internal reference is shown in Figure 13-3. This is controlled by a single
configuration register (ACREFCTL). Table 13-3 shows the programming options to develop
specific internal reference values, to compare an external voltage against a particular voltage
generated internally.
Figure 13-3.
Table 13-3. Internal Reference Voltage and ACREFCTL Field Values
EN Bit Value
EN=0
EN=1
ACREFCTL Register
VREF
RNG
Comparator Internal Reference Structure
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
)
March 22, 2006