LM3S1969 Datasheet, PDF (544/677 Pages) Texas Instruments – Stellaris® LM3S1969 Microcontroller

OBSOLETE: TI has discontinued production of this device.
Analog Comparators
Table 15-1. Analog Comparators Signals (100LQFP) (continued)
Pin Name
Pin Number Pin Type Buffer Type^a Description
C2+
23
I
Analog Analog comparator 2 positive input.
C2-
22
I
Analog Analog comparator 2 negative input.
a. The TTL designation indicates the pin has TTL-compatible voltage levels.
15.3 Functional Description
Important: It is recommended that the Digital-Input enable (the GPIODEN bit in the GPIO module)
for the analog input pin be disabled to prevent excessive current draw from the I/O
pads.
The comparator compares the VIN- and VIN+ inputs to produce an output, VOUT.
VIN- < VIN+, VOUT = 1
VIN- > VIN+, VOUT = 0
As shown in Figure 15-2 on page 544, the input source for VIN- is an external input. In addition to
an external input, input sources for VIN+ can be the +ve input of comparator 0 or an internal reference.
Figure 15-2. Structure of Comparator Unit
- ve input
+ ve input ⁰
1
+ ve input (alternate)
2
reference input
CINV
output
IntGen
TrigGen
ACCTL
ACSTAT
15.3.1
A comparator is configured through two status/control registers (ACCTL and ACSTAT ). The internal
reference is configured through one control register (ACREFCTL). Interrupt status and control is
configured through three registers (ACMIS, ACRIS, and ACINTEN).
Typically, the comparator output is used internally to generate controller interrupts. It may also be
used to drive an external pin or generate an analog-to-digital converter (ADC) trigger.
Important: The ASRCP bits in the ACCTLn register must be set before using the analog
comparators.
Internal Reference Programming
The structure of the internal reference is shown in Figure 15-3 on page 545. This is controlled by a
single configuration register (ACREFCTL). Table 15-2 on page 545 shows the programming options
to develop specific internal reference values, to compare an external voltage against a particular
voltage generated internally.
544
July 24, 2012
Texas Instruments-Production Data