LM3S2620 Luminary Micro, Inc, LM3S2620 Datasheet - Page 437

• Manufacturer Part Number: LM3S2620
• Description: Lm3s2620 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

17.2.5
17.2.6
17.2.7
17.2.8
July 25, 2008
Interrupt Selector
The PWM generator also takes the same four (or six) counter events and uses them to generate
an interrupt. Any of these events or a set of these events can be selected as a source for an interrupt;
when any of the selected events occur, an interrupt is generated. The selection of events allows
the interrupt to occur at a specific position within the PWM signal. Note that interrupts are based on
the raw events; delays in the PWM signal edges caused by the dead-band generator are not taken
into account.
Synchronization Methods
There is a global reset capability that can synchronously reset any or all of the counters in the PWM
generators. If multiple PWM generators are configured with the same counter load value, this can
be used to guarantee that they also have the same count value (this does imply that the PWM
generators must be configured before they are synchronized). With this, more than two PWM signals
can be produced with a known relationship between the edges of those signals since the counters
always have the same values.
The counter load values and comparator match values of the PWM generator can be updated in
two ways. The first is immediate update mode, where a new value is used as soon as the counter
reaches zero. By waiting for the counter to reach zero, a guaranteed behavior is defined, and overly
short or overly long output PWM pulses are prevented.
The other update method is synchronous, where the new value is not used until a global synchronized
update signal is asserted, at which point the new value is used as soon as the counter reaches
zero. This second mode allows multiple items in multiple PWM generators to be updated
simultaneously without odd effects during the update; everything runs from the old values until a
point at which they all run from the new values. The Update mode of the load and comparator match
values can be individually configured in each PWM generator block. It typically makes sense to use
the synchronous update mechanism across PWM generator blocks when the timers in those blocks
are synchronized, though this is not required in order for this mechanism to function properly.
Fault Conditions
There are two external conditions that affect the PWM block; the signal input on the Fault pin and
the stalling of the controller by a debugger. There are two mechanisms available to handle such
conditions: the output signals can be forced into an inactive state and/or the PWM timers can be
stopped.
Each output signal has a fault bit. If set, a fault input signal causes the corresponding output signal
to go into the inactive state. If the inactive state is a safe condition for the signal to be in for an
extended period of time, this keeps the output signal from driving the outside world in a dangerous
manner during the fault condition. A fault condition can also generate a controller interrupt.
Each PWM generator can also be configured to stop counting during a stall condition. The user can
select for the counters to run until they reach zero then stop, or to continue counting and reloading.
A stall condition does not generate a controller interrupt.
Output Control Block
With each PWM generator block producing two raw PWM signals, the output control block takes
care of the final conditioning of the PWM signals before they go to the pins. Via a single register,
the set of PWM signals that are actually enabled to the pins can be modified; this can be used, for
example, to perform commutation of a brushless DC motor with a single register write (and without
modifying the individual PWM generators, which are modified by the feedback control loop). Similarly,
Preliminary
LM3S2620 Microcontroller
437