Advertisement
6.
The following chart shows the clock setting at
the start of various years. The clock settings,
expressed in he'xadecimal notation, correspond
to 0 AM Greenwich Mean Time on January 1
of ,each year.
Year
Clock Setting (Hex)
1900
0000 0000 0000 0000
1976
8853 BAFO B400 0000
1980
8F80 9FD3 2200 0000
1984
96AD 84B5 9000 0000
1988
9DDA 6997 FEOO 0000
1992
A507 4E7A 6COO 0000
1996
AC34 335C DAOO 0000
2000
B361 183F 4800 0000
7.
The stepping value of time-of-day-clock bit
position 63, if implemented, is 2-
12
micro-
seconds, or approximately 244 picoseconds.
This value is called a clock unit.
The following chart shows various time
intervals in clock units expressed in
hexadecimal notation.
Interval
Clock Units (Hex)
1 microsecond
1000
1 mi 11 i second
3E 8000
1 second
F424 0000
1 minute
39 3870 0000
1 hour
D69 3A40 0000
1 day
1 41DD 7600 0000
365 days
lCA E8Cl 3EOO 0000
366 days
lCC 2A9E B400 0000
1,461 d ays l
72C E4E2 6EOO 0000
1 Number of nays in four years,
including a leap year.
Clock Comparator
The clock comparator provides a means of causing
an interruption when thetime-of-day-clock value
exceeds a value specified by the program.
The clock comparator has the same format as the
time-of-day clock. In the basic form, the clock
comparator consists of bits 0-47, which are
compared with the corresponding bits of the
time-of-day clock. In some models, higher
resolution is obtained by providing more than 48
bits. The bits in positions provided in the clock
comparator are compared with the corresponding
bits of the clock. When the resolution of the clock
is less than that of the clock comparator, the
4-18
IBM 4300 Processors Principles of Operation
contents of the clock comparator are compared
with the clock value as this value would be stored
by executing STORE CLOCK.
The clock comparator 'causes an external
interruption with the interruption code 1004 (hex).
A request for a clock-comparator interruption exists
whenever either of the following conditions exists:
1. The time-of-day clock is running and the value
of the clock comparator is less than the value in
the compared portion of the clock, both values
being considered unsigned binary integers.
Comparison follows the rules of unsigned
binary arithmetic.
2. The time-of-day clock is in the error state or
the not-operational state.
A request for a clock-comparator interruption
does not remain pending when the value of the
clock comparator is made equal to or greater than
that of the time-of-day clock or when the value of
the time-of-day clock is made less than the
clock-comparator value. The latter may occur as a
result of the time-of-day clock either being set or
wrapping to zero.
The clock comparator can be inspected by
executing the instruction STORE CLOCK
COMP ARA TOR and can be set to a specific value
by executing the SET CLOCK COMPARATOR
instruction.
The contents of the clock comparator are
initialized to zero by initial program reset.
Programming Notes
1. An interruption request for the clock
comparator persists as long as the
clock-comparator value is less than that of the
time-of-day clock or as long as the time-of-day
clock is in the error or not-operational state.
Therefore, one of the following actions must be
taken after an external interruption for the
clock comparator has occurred and before the
CPU is again enabled for external
interruptions: the value of the clock comparator
has to be replaced, the time-of-day clock has to
be set, or the clock-comparator submask has to
be set to zero. Otherwise, loops of external
interruptions are formed.
2.
The instruction STORE CLOCK may store a
value which is greater than that in the clock
comparator, even though the CPU is enabled
for the clock-comparator interruption. This is
because the time-of-day clock may be
Advertisement
Chapters
