Élan™SC520 Microcontroller User’s Manual 18-1
CHAPTER
18
SOFTWARE TIMER
18.1 OVERVIEW
The software timer is intended to provide a millisecond timebase with microsecond
resolution. Ideal applications for this function include providing a system wide software
timebase, code profiling, and precise measurement of the time between events. Features
of the software timer include:
■ One 16-bit millisecond counter that increments with a period of one millisecond. This
yields a maximum duration of 65.5 seconds. Note that this timer is accurate to the
precision of the 33-MHz crystal used in the system.
■ A microsecond latch register that provides the number of microseconds since the last
time that the millisecond register was read.
■ The 16-bit millisecond counter is reset to zero when it is read.
■ The software timer can be configured to maintain an accurate time when either a 33.000-
MHz or 33.333-MHz crystal is used in the system.
18.2 BLOCK DIAGRAM
Figure 18-1 shows a block diagram of the software timer.
Figure 18-1 Software Timer Block Diagram
Microsecond
33 MHz
Software Timer
/33
1 MHz
Millisecond
Counter
Rollover
Signal
Microsecond
Register
Latch
Latch
Enable
UPCTR
Élan™SC520 Microcontroller
SWTMRMILLI SWTMRMICRO
Up Counter
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