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General Description - RCA Spectra 70 Training Manual

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GENERAL DESCRIPTION
INTRODUCTION
The RCA 70/25 is the intermediate member of the
Spectra 70 Data Processing series.
It
is a powerful
small-to-medium scale data processor.
Equipped
with communications gear, the 70/25 has high-speed,
high-volume message switching or remote processing
capabilitie s.
70/25
PROCESSOR
The RCA 70/25 Processor is a general-purpose,
stored program, digital machine that includes High-
Speed Magnetic Core Memory, Program Control, and
the appropriate Input/Output logic for the Spectra 70
Systems standard Interface Unit.
HIGH-SPEED MEMORY
The High-Speed Memory (HSM) is a magnetic core
device that provides storage and work area for pro-
grams and data. The memory capacity is either
16,384,
32,768,
or 65,536 bytes. A byte is the
smallest addressable unit in memory, and consists
of eight information bits and a parity bit.
Each byte
location maybe accessed with a 16-bit binary address
consisting of two parts: a displacement carried in an
instruction, and a base address stored in a general
register. The sum of the two form an effective mem-
0ry address.
The Memory Cycle is
1.
5 microseconds, which is
the time it takes to transfer four bytes from HSM to
a memory register and to regenerate the bytes
in storage.
PROGRAM CONTROL
The Program Control executes the instructions of
the program stored in the HSM. An instruction can
be interpreted and executed by the Program Control
only after it has been brought out of HSM. The
process of interpreting and placing the components
of the instruction in the proper registers is called
staticizing. An instruction is first staticized and
then executed by the Program Control logic.
AUTOMATIC INTERRUPT
The RCA 70/25 can staticize and execute all instruc-
tions in one of two programming states; the Proces-
sing State and
the
Interrupt State.
The Processing;
State is the normal mode of operation. A condition
that causes interrupt will transfer the computer to
the Interrupt State. Interrupt is mechanized in the
70/25 hardware. It automatically senses the pres-
ence of interrupt conditions, and transfers control to
the Interrupt State.
INSTRUCTION COMPLEMENT
The RCA 70/25 Order Code consists of thirty-one
instructions which can be divided into four classeso
1.
DATA HANDLING
The data-handling instructions allow for the move-
ment of data fields within HSM.
Data may be moved
without changing format or it can be packed, unpacked
or edited for printing during the movement. A Trans-
late instruction facilitates code conversion and data
validation.
2.
ARITHMETIC INSTRUCTIONS
This set includes Decimal Add, Subtract, Multiply
and Divide instructions, as well as Binary Add and
Subtract operations. It also incorporates the ability
to perform Boolean Operations on bit structures.
3.
DECISION AND CONTROL
The decision and control instructions allow for the
comparing of both Decimal and Binary fields, and
the branching to a location in HSM according to a
Condition Code Indicator. Also included are Branch
and Link and Branch-Qn-Count instructions that
simplify subroutine linkage, and control of iterative
coding.
4.
INPUT/OUTPUT
Read and Write instructions transfer data between
the processor and all peripheral equipment on-line
to the 70/25. Included are the necessary instructions
to control the devices and to recognize and recover
from error conditions.
INSTRUCTION FORMAT
There are three basic instruction formats in the
70/25; six-byte, four-byte, and a two-byte instruc-
tion. The first byte of every instruction is the
operation code. Depending on the instruction, the
remaining
byte~
refer to field lengths, register and
storage addresses,
or contain peripheral device
identification.
DATA FORMAT
The basic unit of storage is the byte, which can

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Spectra 70/25