LM3S9D81 Datasheet, PDF (1111/1277 Pages) Texas Instruments – ARM and Thumb are registered trademarks and Cortex

Stellaris^® LM3S9D81 Microcontroller
As shown in Figure 20-2 on page 1111, the input source for VIN- is an external input, Cn-. In addition
to an external input, Cn+, input sources for VIN+ can be the C0+ or an internal reference, V_IREF.
Figure 20-2. Structure of Comparator Unit
- ve input
+ ve input ⁰
+ ve input (alternate) ¹
2
reference input
CINV
output
IntGen
TrigGen
ACCTL
ACSTAT
20.3.1
A comparator is configured through two status/control registers, Analog Comparator Control
(ACCTL) and Analog Comparator Status (ACSTAT). The internal reference is configured through
one control register, Analog Comparator Reference Voltage Control (ACREFCTL). Interrupt
status and control are configured through three registers, Analog Comparator Masked Interrupt
Status (ACMIS), Analog Comparator Raw Interrupt Status (ACRIS), and Analog Comparator
Interrupt Enable (ACINTEN).
Typically, the comparator output is used internally to generate an interrupt as controlled by the ISEN
bit in the ACCTL register. The output may also be used to drive an external pin, Co or generate an
analog-to-digital converter (ADC) trigger.
Important: The ASRCP bits in the ACCTL register must be set before using the analog comparators.
Internal Reference Programming
The structure of the internal reference is shown in Figure 20-3 on page 1111. The internal reference
is controlled by a single configuration register (ACREFCTL).
Figure 20-3. Comparator Internal Reference Structure
VDDA
8R
R
8R
R
R
•••
EN
VREF
RNG
15 14
•••
1
0
Decoder
internal
reference
VIREF
The internal reference can be programmed in one of two modes (low range or high range) depending
on the RNG bit in the ACREFCTL register. When RNG is clear, the internal reference is in high-range
mode, and when RNG is set the internal reference is in low-range mode.
January 23, 2012
Texas Instruments-Production Data
1111