Chapter 4. CPU Operation
GFK-2222AD
April 2018
157
4.8
Clocks and Timers
Clocks and timers provided by the CPU include an elapsed time clock, a time-of-day clock, and software
and hardware watchdog timers.
For information on timer functions and timed contacts provided by the CPU instruction set, refer to
Timers
in
PACSystems RX7i, RX3i and RSTi-EP
CPU Programmer’s Reference Manual,
GFK-2950 Chapter
4.
4.8.1
Elapsed Time Clock
The elapsed time clock tracks the time elapsed since the CPU powered on. The clock is not retentive
across a power failure; it restarts on each power-up. This seconds count rolls over (seconds count returns
to zero) approximately 100 years after the clock begins timing.
Because the elapsed time clock provides the base for system software operations and timer function
blocks, it may not be reset from the user program or the programmer. However, the application program
can read the current value of the elapsed time clock by using Service Request #16 or Service Request
#50, which provides higher resolution.
