LM3S818 Datasheet, PDF (447/572 Pages) Bookham, Inc. – Microcontroller

Stellaris^® LM3S818 Microcontroller
the possible GPIO pin placements for the Analog Comparator signals. The AFSEL bit in the GPIO
Alternate Function Select (GPIOAFSEL) register (page 249) should be set to choose the Analog
Comparator function. The positive and negative input signal are configured by clearing the DEN bit
in the GPIO Digital Enable (GPIODEN) register. For more information on configuring GPIOs, see
“General-Purpose Input/Outputs (GPIOs)” on page 230.
Table 13-1. Analog Comparators Signals (48QFP)
Pin Name
Pin Number Pin Type Buffer Type^a Description
C0+
42
I
Analog Analog comparator 0 positive input.
C0-
44
I
Analog Analog comparator 0 negative input.
C0o
43
O
TTL
Analog comparator 0 output.
a. The TTL designation indicates the pin has TTL-compatible voltage levels.
13.3 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 13-2 on page 447, 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 13-2. Structure of Comparator Unit
- ve input
0
+ ve input
1
+ ve input (alternate)
2
reference input
CINV
output
IntGen
TrigGen
ACCTL
ACSTAT
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). The operating modes of the
comparators are shown in the Comparator Operating Mode tables.
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.
July 14, 2014
447
Texas Instruments-Production Data