RCA 70/46 User Manual

OPTIONAL
FEATURES
FEATURE 500 1-46
MEMORY PROTECT
Operational
Characteristics
FEATURE 5002-46
ELAPSED TIME
CLOCK
Operational
Characteristics
• Data in memory can be protected from destruction or intrusion by the
erroneous storing or fetching of information during program execution
through the optional Memory Protect feature. This feature provides store
protection or store and fetch protection for memory blocks of 2,048
bytes each.
• Memory protection is accomplished by a five-bit storage key associated
with each block of 2,048 bytes of main memory. Whenever data is to be
stored
or accessed in main memory during the execution of an instruction,
the five-bit protection key in the Interrupt Status register for the current
program state is compared with the five-bit storage key. During a channel-
to-memory
data transfer, the protection key (as specified in the channel
address word) is compared with the storage key. If the storage and
protection keys are equal, or either one is zero, the storage or access of
data is completed.
If the storage and protection keys do not match (neither is zero),
the execution of an instruction that stores data into memory or accessor
data is suppressed or terminated. An address error (protection) interrupt
occurs, and the protected memory remains unaltered. If the storage and
protection keys mismatch during a channel-to-memory data transfer, the
data transfer is terminated and a channel termination interrupt occurs.
The protected memory is
unaltered and the indication of mismatch is stored
in the input/output channel registers in scratch-pad memory for the
specified channel.
The storage key can be changed by the privileged instruction Set
Storage Key and can be inspected by the privileged instruction Insert
Storage Key.
When
the Memory Protect feature is not installed and the protection
key is non zero,
an address error (specification) interrupt occurs.
• The elapsed time clock is an optional feature available on the 70/46
Processor.
• The elapsed time clock occupies a full word beginning at main memory
location 80. The word is treated as a signed binary operand and follows
the rules of fixed-point arithmetic.
The clock count is performed by decrementing bit positions 21 and 23
every
1/60th of a second (60 cycle processor) or by decrementing bit
positions 21 and 22 every 1/50th of a second (50 cycle processor) . In either
case, the effect is equivalent to reducing the elapsed time clock by one in
bit position 23 every 1/300th of a second (every 3.3 milliseconds). When the
clock goes from positive to negative, an elapsed time clock interrupt occurs.
Normally,
an updated elapsed time clock is available after the com-
pletion
of each instruction execution. However, when input/output data
transmission approaches the limit of main memory capability, or a Read
Direct instruction time is excessive, elapsed time clock updating can
be skipped.
220

RCA 70/46 Specifications

General

Brand	RCA
Model	70/46
Category	Computer Hardware
Language	English