LM3S9B81 Datasheet, PDF (1005/1155 Pages) Texas Instruments – Stellaris® LM3S9B81 Microcontroller

Stellaris® LM3S9B81 Microcontroller
As shown in Figure 21-2 on page 1005, 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 21-2. Structure of Comparator Unit
- ve input
+ ve input ⁰
+ ve input (alternate) ¹
2
reference input
CINV
output
IntGen
TrigGen
ACCTL
ACSTAT
21.3.1
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 21-3 on page 1005. The internal reference
is controlled by a single configuration register (ACREFCTL). Table 21-3 on page 1006 shows the
programming options to develop specific internal reference values, to compare an external voltage
against a particular voltage generated internally (V_IREF).
Figure 21-3. Comparator Internal Reference Structure
VDDA
8R
R
8R
R
R
•••
EN
VREF
RNG
15 14
•••
1
0
Decoder
internal
reference
VIREF
June 29, 2010
Texas Instruments-Advance Information
1005