The operation of the clock is not affected or inhibited by
any normal activity or event in the system. The clock runs
when the CPU is in the wait or stopped state or in the
instruction-step, single-cycle, or test mode. Its operation is
not .affected by system reset or the IPL procedure.
Depending on the implementation, the clock mayor may
not run with CPU power off.
Three states are distinguished for an operational clock:
set, not-set, and error. The state determines the condition
code set by STORE CLOCK.
When the power for the clock is turned on, the value of
the clock is set to zero, and the clock enters the not-set
state.