IS220PAICH2A GE System software operation

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.

A hardware time-of-day clock maintains the time of day (TOD) in the CPU. The time-of-day clock

maintains the following time functions:

▪ Year (two digits)

▪ Month

▪ Day of month

▪ Hour

▪ Minute

▪ Second

▪ Day of week

The TOD clock is battery-backed and maintains its present state across a power failure. The time-of

day clock handles month-to-month and year-to-year transitions and automatically compensates for

leap years through year 2036.

You can read and set the hardware TOD time and date through the application program using

Service Request function #7. For details, refer to PACSystems RX7i, RX3i and RSTi-EP CPU

Programmer’s Reference Manual, GFK-2950 Chapter 6.

High-Resolution Time of Day Software Clock

A high-resolution software TOD clock is implemented in firmware to provide nanoseconds resolution.

When the high-resolution software TOD clock is set, the hardware TOD clock is set with the YYYY:

Mon: Day: Hr: Min: Sec fields in the POSIX68 time, the RTC is read, and the delta between the

POSIXtime and the value read from the RTC is computed and saved. Thus, if 1-second resolution is

desired the hardware TOD clock is read. Otherwise, the high-resolution software TOD clock is read to

provide greater resolution. When the latter occurs, the hardware RTC is read and the saved delta

added to the value read.

When the SNTP Time Transfer feature is implemented, all SNTP time updates received at the CPU will

cause the high-resolution software TOD clock to be updated.

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