LM3S812_16 Datasheet, PDF (497/590 Pages) Texas Instruments – Stellaris LM3S812 Microcontroller

Stellaris^® LM3S812 Microcontroller
Figure 15-2. PWM Module Block Diagram
PWM Generator Block
Interrupts /
Triggers
Control
PWMnCTL
Timer
zero
load
dir
PWMnLOAD
PWMnCOUNT
PWM Clock
Comparators
PWMnCMPA
PWMnCMPB
cmp A
cmp B
Interrupt and
Trigger
Generator
PWMnINTEN
PWMnRIS
PWMnISC
Signal
Generator
PWMnGENA
PWMnGENB
Fault
Condition
PWMnFLTSRC0
PWMnMINFLTPER
PWMnFLTSEN
PWMnFLTSTAT0
Fault(s)
PWMn_Fault
Dead-Band
Generator
PWMnDBCTL
PWMnDBRISE
PWMnDBFALL
PWMn_A
PWMn_B
15.2
Signal Description
Table 15-1 on page 497 lists the external signals of the PWM module module and describes the
function of each. The PWM controller signals are alternate functions for some GPIO signals and
default to be GPIO signals at reset. The column in the table below titled "Pin Assignment" lists the
possible GPIO pin placements for these PWM signals. The AFSEL bit in the GPIO Alternate Function
Select (GPIOAFSEL) register (page 250) should be set to choose the PWM function. For more
information on configuring GPIOs, see “General-Purpose Input/Outputs (GPIOs)” on page 230.
Table 15-1. PWM Signals (48QFP)
Pin Name
Pin Number Pin Type Buffer Type^a Description
Fault
47
I
TTL
PWM Fault.
PWM0
25
O
TTL
PWM 0. This signal is controlled by PWM Generator 0.
PWM1
26
O
TTL
PWM 1. This signal is controlled by PWM Generator 0.
a. The TTL designation indicates the pin has TTL-compatible voltage levels.
15.3 Functional Description
15.3.1
PWM Timer
The timer runs in one of two modes: Count-Down mode or Count-Up/Down mode. In Count-Down
mode, the timer counts from the load value to zero, goes back to the load value, and continues
counting down. In Count-Up/Down mode, the timer counts from zero up to the load value, back
down to zero, back up to the load value, and so on. Generally, Count-Down mode is used for
generating left- or right-aligned PWM signals, while the Count-Up/Down mode is used for generating
center-aligned PWM signals.
The timers output three signals that are used in the PWM generation process: the direction signal
(this is always Low in Count-Down mode, but alternates between Low and High in Count-Up/Down
July 14, 2014
497
Texas Instruments-Production Data