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Macroinstructions.
The macro-assembler program
within the DXIO operating system allows the user to
define macroinstructions that activate assembly-
language subroutines. If a particular application
program requires repetitive use of an instruction
sequence, the sequence can be incorporated into a
macroinstruction definition and activated by
reference to the macroinstruction.
Macroinstructions differ from XOPs in that
macroinstructions are defined at assembly time and
may be local to a given application program. XOPs
must
be
defined at DXIO system-generation (sysgen)
time and can apply to all application programs.
990 CPU On-Board Loader
A loader is a short, simple program that contains
the instructions required to read other programs
from an input device to memory. The basic
requirements for a loader are
(1)
that it not be
altered by power interruption and (2) that it be
either permanently resident in main memory or
readily loaded by hardware action.
The 990 CPU is supplied with a I024-byte loader
ROM devices. The loader is activated by the front-
panel LOAD switch to initiate a bootstrap read of
the DXIO operating system from a disk-storage
system. The loader also can load the DXIO
operating system from a 733 ASR terminal cassette,
an 804 card reader, or a 979A magnetic-tape
transport. The ROM loader includes a programmer-
panel management utility, which controls the front-
panel indicators and accepts panel-switch commands.
Purchasers of DS990 hardware-only systems may
wish to use a different loader or to "burn" their own
loader programs. Texas Instruments offers a variety
ill ·loatiers-
-as-
standard price;;;hst· items- and· offers· a
device kit, which consists of two 256-word by 8-bit
programmable read-only memories. The maximum
limit of two device kits (1024 bytes) is determined by
socket space on the logic board.
Programmer Panel
The programmer panel is a CR U device, which
contains logic, switches, and indicators that allow
user control and observation of computer operations.
Functions of the indicator lights and switches are
defined by panel firmware included in the standard
disk-loader ROM. The built-in programmer-panel
logic includes a switch debounce timer. The
programmer-panel logic is connected to the 990 CPU
by a 20-conductor flat cable.
The three-position, key-operated POWER OFF,
LOCK, UNLOCK switch at the left side of the
panel controls the computer system's ac power and
42
prevents the inadvertent halting of the computer.
The key can be removed from the lock when the
switch is in either the POWER OFF or LOCK
position. When the switch is in the POWER OFF
position and the key is removed from the lock, no
unauthorized turn-on of the computer can occur.
When the switch is in the LOCK position, the other
programmer-panel switches are locked out and
cannot start, stop, or otherwise affect computer
operation. The programmer panel is operable, and
manual control from the panel can be exerted with
the key lock in the UNLOCK position.
990 Memories
DS990 systems are supplied with a minimum of
128K bytes of error-checking-and-correcting (ECC)
16K semiconductor memory. This random-access
read/write memory (RAM) is required for operating-
system storage, application-program and data
storage, workspace-register I/O buffering, and
execution scratch-pad areas. The DXIO operating
system rolls programs and overlays between the disk
and memory to manage the available memory space
for best use and minimum execution time.
Additional me.i11ory
may
~
required
in systems with
mUltiple VDTs. However, the 990 system has a
2048K-byte maximum memory-addressing capability.
The devices used for 990 memory expansion are
the 16K dynamic RAMs. The term RAM refers to
read / write memory in which access time to any two
storage locations is the same. A dynamic RAM
requires periodic refreshing of the stored data; this is
performed automatically by the memory-board logic.
The refresh circuits steal one memory cycle each
15.5
microseconds. The refresh operation is transparent to
the user.
The dynamic-RAM devices used in the 990
memory are the most reliable memory components
available today. However, good system design
requires some form of error correction for large
memories. The DS990 system uses ECC memory for
greater reliability. A unique 6-bit Hamming code is
attached to each 16-bit word stored in memory. This
code permits automatic (hardware) detection and
correction of all I-bit errors and detection of all 2-
bit errors.
Automatic correction of I-bit errors allows the
system to operate normally despite a failure that
would otherwise require immediate service. Repair of
failed memory modules usually can be deferred to
regular maintenance periods, thus reducing
downtime.
The basic ECC memory consists of an ECC
controller board with the necessary TILINE interface
logic, refresh control, error-detection-and-correction
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