Input/Output Control; Interval Timer - RCA 70/46 Reference Manual

INPUT /OUTPUT
CONTROL
INTERVAL TIMER
System Structure
• The RCA 70/46 Processor communicates with all input/output devices
through the RCA standard interface.
The 70/46 Processor can have
up
to four selector channels (optional).
Each selector channel contains two standard interface trunks. Each stand-
ard interface trunk controls one device subsystem (from 1 to 16 devices).
All selector channels can operate simultaneously.
In addition to the selector channels, a multiplexor channel is standard
equipment on the 70/46 Processor.
The multiplexor channel on the 70/46 contains eight standard interface
trunks. Each trunk controls one device subsystem. All trunks on the multi-
plexor channel can operate simultaneously. Also, the multiplexor channel
and all selector channels can operate simultaneously.
• The 70/46 has a variable 16-bit Interval Timer which can be set and
read by the program. Upon being set to a nonzero value, the least significant
bit position of the timer is decremented by one every 100 microseconds
until its count becomes zero. Further decrementing is suppressed and the
Interval Timer (Flag Position 12) interrupt is effected, subject to the
corresponding mask. The Interval Timer runs when set to a nonzero
value; otherwise it does not run. 'The decrement of the count occurs such
that the total elapsed time is never less than the count set in the Interval
Timer. The maximum possible time interval is not greater than 100 micro-
seconds more than the loaded count. This timer is not available to 70/35,
70/45, and 70/55 programs.
The Interval Timer is an independent unit capable of being read and
loaded by Special Functions. Decrementation occurs simultaneously with
processing and causes no interference to either processing (except for
program interrupt upon lapse of count) or I/O servicing. When the proces-
sor is halted, the Interval Timer decrementing is stopped. General reset
causes the Interval Timer to be reset to zero.
Note: Use of the Interval Timer and Diagnostic Snapshot by programs
may not occur together because 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 func-
tion 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.
8