RCA 70/46 Reference Manual page 106

Special Function #4
Load Interval Timer
(LIT)
General Description
I Code
Privileged
Instructions
• This Special Function loads the Interval Timer with a halfword. 'The
address of the halfword to be loaded is indicated by the contents of the
memory location addressed by the address field of the Function Call instruc-
tion. If the value loaded is a nonzero value, the timer begins to decrement
by one. If the value loaded is zero, and the timer is not counting, the
instruction has no effect. If this instruction is executed while the timer is
running, the contents of the counter are replaced by the specified halfword.
If the specified halfword is zero, the timer is reset to zero (shut-off) and
no interrupt occurs for this condition.
• 02.
Format Base
Displacement
Condition Code
Interrupt Action
Notes
0 3 4
• Unchanged.
• Address Error.
Power Failure.
Machine Check.
Paging Error.
Paging Queue.
15
• 1.
If either this Special Function or the timer halfword addresses are
not on halfword boundaries, an Addressing Error Interrupt condi-
tion occurs.
2. If the counter is reset to zero after zero occurs and the interrupt
flag has been set, the interrupt flag will not be cleared.
3. Use of the Interval Timer and Diagnostic Snapshot by programs
may not occur together, since the counter register is common to both.
If the Diagnose function is initiated while the Interval Timer is
running, the shared counter is cleared to zero without occurrence
of the Interval Timer Interrupt and the Diagnose function assumes
control of the counter. If the function being diagnosed is the Load
Interval Timer, the actual loading of the counter is inhibited but
the E. O. Flow is Diagnosed.
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