path: root/doc/rfc/rfc296.txt

Network Working Group                                          D. Liddle
Request for Comments: 296                           Owens-Illinois, Inc.
NIC: 8484                                                   January 1972

                          DS-1 DISPLAY SYSTEM

Introduction

   This document describes a proposed modular graphic/alphanumeric
   display system containing a 512 x 512 line, 60 line per inch plasma
   display/memory panel and a mini- processor.  It is intended to
   combine the advantages of display memory and local processing power
   to operate in three general modes as follows:

   1. As an "intelligent terminal" operating on data received from the
      network or a local host to perform text editing, picture
      processing, etc.

   2. As a passive terminal in which the mini-processor translates
      existing display lists, command strings and data structure for
      storage tube terminals or other devices into the proper form to
      operate the plasma display.  In particular, a software module for
      simulation of the ARDS 100A is provided.

   3. As an offline system, where the processor is operated as a stand-
      along mini-computer for debugging, editing, and general display
      work.

   The DS-1 consists of a display module, a processor module, and
   keyboard (see Figure 1).  The display model is a DIGIVUE_
   display/memory unit, model 512-60, produced by Owens-Illinois, Inc.,
   containing the plasma panel and associated drive circuitry.  The
   processor module was specially designed and built for the DS-1
   application by the Raytheon Company.

   A modem is enclosed in the processor module, and is described in
   later sections.  An alternative RS 232 interface is also available
   for connection to a TIP or teletype compatible system.

   [Figure 1 DS-1 Display System*]

   In addition to the display module and the processor, the DS-1 has a
   modem for data transmission, and Ascii keyboard, and an I/0 interface
   to support numerous external devices.  The mechanical design of the
   DS-1 emphasizes flexibility, so that both the keyboard and display
   module can be oriented independently of the processor module.





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   Software will be supplied with the DS-1, for such functions as text
   editing, vector generation, data management and various I/0 routines.

   The DS-1 is intended principally to operate as an online terminal;
   the offline mode is used for programming and data preparing chores
   which do not require access to the host computer.  In describing
   system operation, therefore, offline operations are simply a subset
   of online operations in which the only I/0 functions are local.  The
   I/0 operations are accomplished by "direct" input/output
   instructions, a special feature of the 700 series machines developed
   at the Raytheon Company.  A single instruction (DIN for input, DOT
   for output) enables the external device addressed by the instruction
   to accept the data presently in the accumulator (DOT) or to transmit
   data to the accumulator (DIN) over the data buss.

   The plasma display X and Y address registers are seen as output
   devices by the processor; the other basic output device is the modem.
   The keyboard and input modem are the basic input devices, in addition
   to the optional cassette tape system for program loading.  These
   devices, and the interfacing of other peripherals are described in
   later sections.

   Figure 2 is a block diagram of the basic DS-1 configurations,
   emphasizing the I/0 structure.  The principal role of the processor
   module is in the restructuring of input data to an appropriate output
   form, either from modem-to-display (computer to operator) or
   keyboard-to-modem (operator to computer).  Such processing consists
   of handling communication chores,

   [Figure 2 US-1 I/0 Configuration*]

   string and stack manipulation, character suppression or translation,
   vector construction from endpoint data or character-encoded line
   drawing commands, and data stream protocol and management, so that
   the input/output character stream over the modem or channel remains
   compatible with the host computer, while the keyboard inputs and
   display outputs are being effectively and efficiently handled.

   The real significance of the DS-1 as a new display terminal stems
   from its use of the plasma display/memory unit.  Because of its
   inherent memory and selective erase capability, it can be addressed
   asynchronously, requires no special "refresh" or access to buffer
   memory, and is indistinguishable from any other output medium, such
   as tape, etc.  Seen from the operator's point of view, it has very
   desirable human factors, such as high contrast and "crisp" line
   dimensions, no jitter, flicker, or distortion, and the capability for
   rear projection of pictorial or tabular data from slides or
   microfiche, for example.



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   Both the display module and the processor are described in details in
   subsequent sections, as well as the mechanical construction,
   communication interfaces, keyboard, and the system software.

   Section 2. Display Module

   The DS-1 display module is an Owens-Illinois DIGIVUE_ display/memory
   unit Model 512-60.  It contains the plasma panel, drive electronics,
   and display logic.  These three assemblies are described in the
   following paragraphs.

   PANEL

   The DIGIVUE_ display panel (or plasma panel) is a matrix device.  It
   is constructed from two pieces of 1/4" plate glass, upon which very
   fine gold electrode lines are deposited.  These electrodes are then
   completely covered by a dielectric film.  These two plates are then
   sealed together with a gap of a few thousandths of an inch between
   them, and with their electrode patterns orthogonally oriented.

   This "sandwich" is then baked out and pumped down to high vacuum,
   backfilled with a gas mixture consisting largely of Neon, and sealed
   off.  The addition of flexible ribbon cable connectors completes the
   fabrication of the panel.  The device is fat, roughly _" thick, and
   virtually transparent.

   The panel is operated in such a way that any location (i.e., any x, y
   intersection) may be individually turned "on" or "off" as a source of
   visible light.  Further, such a location has a "memory" and is
   sustained in the 'on" or "off" state until a new selection signal
   changes it.

   An AC voltage is applied between all x and all y electrodes in
   parallel, so that an AC signal less than the breakdown potential is
   applied across the gas at all times.  This is called the sustaining
   voltage, VS.  When a single x,y point is to be addressed, a voltage
   pulse, VP, is applied to the appropriate x and y lines, such that the
   total addressing voltage at their intersection is given by

                             V ADD = VS + 2VP,

   which exceeds the breakdown potential of the gas, initiation a
   discharge.

   Since the electrodes are covered by a dielectric, no discharge
   current can flow in the external circuit.  Rather, the ions and
   electrons produced by the discharge are carried by the applied field
   and are deposited as stored charge on the dielectric surfaces, until



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   the resultant net field is nearly zero, quenching the discharge after
   about one microsecond.  As the AC sustaining voltage changes
   polarity, however, this stored charge constitutes a bias voltage,
   adding to the sustaining signal and producing a new discharge, which
   results in stored charge causing another discharge on the next half
   cycle, etc.  Thus, once addressed, a single x,y location continues to
   produce a discharge twice in every sustainer period, or about 100
   thousand times per second.  Naturally, this appears as a continuous
   glow to the eye.  A sustained location may be turned off by
   addressing in such a way that the stored charge is allowed to return
   to zero.  Thus, a location, or 'cell", may be turned on or off in a
   bistable, random access manner.

   The plasma display has a number of extremely useful visual
   characteristics.  Its transparency permits the use of rear-projected
   data from microfilm, color slides, maps, forms, etc., to be "mixed"
   with the dynamic, computer generated data to be displayed
   (characters, plots, graphics, etc.). In addition to the high
   brightness of the gas discharge, the contrast ration is extremely
   nigh.  The panel used in the model 512-60 has 512 x 512 lines at 60
   lines per inch.  This high resolution and large size allows highly
   readable characters and graphics to be mixed, without distortion or
   jitter of the data.  Dot matrix characters are especially attractive,
   since the "dots" of the discharge sites have very clean, crisp
   dimensions.

   A significant system characteristic of the plasma display matrix is
   its random access memory property.  Unlike storage tube displays, it
   may be selectively erased as well as written, changing a single
   point, curve, or character without altering the contents of other
   locations on the panel.  Large quantities of text, time histories of
   measured data, or complex memory.  This allows more efficient use of
   the processor and simpler data management within computer memory.

   The 512-60 panel used in the DS-1 application will have an active
   area of 8.5 x 8.5 inches, containing 512 x 512 lines.  There will be
   an additional 4 line peripheral border around the addressable area to
   provide conditioning of the discharge sites.

   The back of the panel will be frosted with an optically diffusing
   surface suitable for the projection of optical images.  A
   circularly-polarizing neutral density filter with anti-glare coating
   will be provided on the front of the display.  The brightness and
   contrast will be sufficient for use in a normal lighted laboratory
   area.






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   Drive Electronics

   The Drive electronics for the display module will be the standard
   Owens-Illinois circuits requri3ed to operate a 512 x 512 line panel
   as part of our model 512-60 standard display unit.  They consist of a
   sustaining generator, which maintains cells, once addressed, in the
   appropriate state ("on" or "off") after removal of the addressing
   signal, and pulse-forming circuits for the generation and appropriate
   mixing of addressing pulses at the selected panel sites.

   The sustainer will operate with a basic period of 20 microseconds,
   with a peak voltage of approximately 130 volts.  Exact voltage
   levels, frequency and waveshape are adjusted for optimal performance
   subject to power supply constraints and data rate requirements.

   The address circuits are multiplexed to reduce the number of active
   circuits required and employ a non-linear mixing scheme for line
   selection.  A pulse of 100 volts is applied with the proper time
   phase to achieve writing and erasing.  The pulse is disabled in all
   but the selected line pair.

   Provision is also made for bulk erasure in which the entire panel is
   erased in two sustainer periods.  A power supply of high density
   design will provide the necessary sustaining, addressing, and logical
   level voltages.  The design will employ high-frequency invertors and
   switching regulation for maximum efficiency and reduced size.  It
   requires about 250 watts, and will be housed inside the processor
   module.

   Display Logic

   The logic included in the display module provides the timing and
   control required for the sustaining generator and the address pulses,
   and also provides the logic level interface to the processor module.
   The interface is TTL compatible.  It contains 2 nine-bit address
   ports X0-X8 and Y0-Y8, which [not legible*], in absolute binary code
   the x,y intersection which is to be addressed.  These addresses are
   accepted when given a write command or an erase command by the
   control lines W or E, respectively.  These inputs must all be held
   steady until acceptance of the data and completion of the operation
   has been indicated by the status line, a logic level output from the
   display unit.  Ad additional control line, B, is used in conjunction
   with the H line to cause a bulk erasure of the entire screen.








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   The model 512-60 display unit proposed in this document is of the
   serial address type, and thus can write or erase a single point each
   20 u/seconds.  This permits vectors to be drawn at more than 800
   inches/second.  Characters in a 5x7 dot matrix can be written at a
   rate of about 1400 characters per second.

   A parallel address type display unit is presently being developed at
   Owens-Illinois.  This module, when available, will be compatible with
   the DS-1 system with no modification to the processor required.  This
   display will address 16 lines in parallel, which will allow more than
   6,000 characters per second to be displayed, or a complete page to be
   generated in .330 seconds.

   Section 3 Processor Module

   The Processor is a minicomputer (Figure 1) that accepts ASCII encoded
   commands and generates outputs to control the writing of information
   by the display module.  The Processor performs the functions of
   storing information, data and instructions and regulating the flow of
   information between the terminal's Keyboard, Modems, Display Module,
   and Program Loading Device (Figure 2).

   In a typical operation, the processor calls up input commands from
   the modem and the keyboard and generates instructions to the display
   module driver circuitry to produce the required characters, vectors,
   or editing programs.

   Instructions and data are stored in 16 bit words.  Arithmetic
   functions are performed in 2's complement form.  The basic machine
   cycle time is 1.6 microseconds.

   The major functional units of the processor are: (Figures 3 & 4)

   o  Memory

   o  Memory Address Register

   o  Program Counter

   o  Instruction Register

   o  Accumulator

   o  Instruction Processing Synchronizer

   o  Terminal I/O Circuitry

   These units are briefly described next.



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   Memory

   An operational memory of 2048 - 16 bit words plus bootstrap memory of
   64-16 bit words are provided.  The 2038 word memory is a Random
   Address Memory (RAM) and is used to store the character generator,
   the vector generator, and the editing programs needed to provide the
   specific operational requirements of the terminal.  Using the RAM
   type memory provides the flexibility

   [Figure 3 Processor Data Flow*]

   [Figure 4 Instruction Processor Synchronizer*]

   to alter instruction routines and to tailor the terminal for the
   application.  Since the terminal uses RAM, an operational program
   loading device (a magnetic tape cassette read/write recorder) is
   proposed so that the operational program can be loaded when the
   terminal is turned on.

   The RAM size is sufficient to permit storage of 128 characters, a
   vector generation routine and an instruction set.

   The bootstrap memory is provided for storing a terminal start up
   program that puts the terminal in a state for reading instruction
   data into its operational memory from external sources.  Read Only
   Memory (ROM) devices are used for the bootstrap memory.  Both the RAM
   and the ROM memories are made up entirely of MOS.

   Memory Address Register

   The Memory Address Register (MA) is a twelve bit register that can be
   loaded with the program counter or the address portion of the memory
   data.

   Program Counter

   The Program Counter (PC) is a 12 bit counter-register that can be
   loaded with the address portion of the instruction register.

   Instruction Register

   The Instruction Register (IR) is a 16 bit register of which 4 bits
   contain the instruction and 12 bits the data associated with the
   instruction.  This can be loaded with a 16 bit memory word.







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   Accumulator (AC)

   The Accumulator (AC) is a 16 bit shift register that can be loaded
   with the contents of the program counter, the data inputs, or the
   arithmetic unit.

   Instruction Processing Synchronizer (IPS)

   The Instruction Processing Synchronizer controls the timing and data
   flow in the processor.  Clocked by its own oscillator, the IPS calls
   up instructions from the memory, which then dictates the sequence to
   be followed.

   Terminal I/O Circuitry

   The processor communicates with the other elements of the terminal
   either directly on the I/O bus or via one of three device
   controllers.  The controllers are required to make the I/O devices
   compatible with the processor.  Separate controllers are provided for
   Keyboard, Display Module, and Serial I/O devices.

   The I/O Bus includes:

   o  16 Parallel Input Data Lines

   o  16 Parallel Output Data Lines

   o  4 lines for selecting the I/O device to communicate with the
      processor

   o  4 Lines for specifying the function to be performed

   o  16 sense lines for monitoring the status of each I/O device

   o  2 strobe lines to initiate the transfer of data to and from the
      I/O devices

   o  1 system clock line

   Each of these lines are available at the I/O Bus Connector.  The
   lines required by each controller varies with the function performed
   by the controller (Figure 4).  Three ports are provided with the
   Serial I/O Channel Controller, two asynchronous and one synchronous.
   The latter is for use with an optional cassette tape recorder that
   can be either supplied as an option with the terminal or purchased at
   a later date.  The two asynchronous ports are for interface with a





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   teletypewriter modem (not supplied) and a telephone modem that is
   supplied with the terminal.  Direct connection with a data processing
   machine ca be accomplished at the I/O bus connector.

   The processor provides a single level interrupt that causes the
   processor to transfer control to a designated sub-program while
   automatically storing the contents of all appropriate registers and
   the return linkage.  The mask and unmask instructions cause the
   interrupt line to be gated according to the state of an inhibit
   flip-flop.  The last instruction (Interrupt Return) restores the
   program counter, accumulator, and overflow indicator to the condition
   existing at the time of interrupting.

   Software

   The desired terminal operations, that is, the logical capabilities of
   the display terminal will be implemented in software.  This approach
   provides a degree of flexibility and versatility to the terminal's
   editing and display writing capability.  In the latter area, the
   generation and display of characters, symbols, and graphics are
   limited in variety only by the resolution (60 dots per inch) and the
   size (8-1/2" x 8-1/2") of the display screen.  The flexible nature of
   this approach is enhanced by the expandability of the memory to 4K
   (32K optional).

   The software is divided into two segments: (1) servicing routines for
   the input modem, the output modem, the keyboard, and the display
   module and (2), specific function routines for line generation,
   editing, point generation, and character generation.

   Typical software processing starts with the program in an idle loop
   checking the input sense line.  When a bit is ready in the modem, the
   sense line goes true, the processor skips and the program inputs the
   bit.  The sense line resets.  The program counts the bit, saves it,
   and returns to an idle loop waiting for subsequent bits.  As each bit
   is input, it is stored in proper sequence.  When a word is entirely
   memory, it is moved to another memory location where it can be
   decoded.  The program resets the input, counts for the next word, and
   transfers to the task routine which analyzes the command and
   determines which segment of the program is to perform the function.

   For this case, assume that the program was instructed to plot a
   character.  The program computes a table from the value of the
   character code.  The table contains a compacted image of the dots
   representing the character.  The image is unpacked from the table
   into a temporary hold area.  Then, starting at the top left corner,
   the program outputs the coordinates and the one or zero value of the
   image.  The next point is output in the next lower Y position.  The



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   process is repeated until 14 bits have outputted (one column).  The
   program resets the Y coordinate to the original Y and increments the
   X.  The next column is output the same as the first.

   When nine columns have been output, the program returns to the idle
   loop.

   Instruction Description

   Instructions and data are in the form of 16 bit words.  Arithmetic
   functions are performed in 2's complement form.  The following word
   formats are applicable:

   Instruction              0  1  3  4     15
                            I   OP    Address

   Address Data             0  1           15
                            I     Address

   Data                     0 1            15
                            S      Data

   The instruction format provides 1 bit to indicate indirect
   addressing, 3 bits for the operations code (OOP) and 12 bits for the
   address.  The address data format contains 15 bits of address and 1
   bit for indicating indirect addressing.  The data word format
   includes 1 sign bit and 15 bits for data.

   Logical control of data flow in the display processor is centered
   about the accumulator, with the majority of the operations involving
   it, or the sensing of data conditions involving the accumulator.  The
   19 processor operations represent 6 types of instructions:

   o  Data Movement (Through the accumulator)

   o  Logical operations (on accumulator contents)

   o  Condition Checking

   o  Input/Output

   o  Jump Control

   o  Indexing

   Each of these instruction types are briefly discussed next.  Refer to
   Appendix I for a complete description of the instruction set.




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              Data Movement Instructions - CLA, LDA, ADD, STC

   These four instructions: enable the accumulator to be cleared or to
   be loaded with data; effect the addition of a word to the
   accumulator's contents; and enable the accumulator contents to be
   stored in memory.

                  Logical Operations - AND, CMP, RAL, SAL

   These four instructions: enable a word in memory to be logically
   "anded" to the accumulator; permit the 2's complement of the
   accumulator's contents to be formed; enable a left rotation of the
   accumulator contents, and permit a left shift of the accumulator's
   contents to be made.

               Condition Checking - SAZ, SNZ, SAC, SNA, SNO

   These five instructions allow for various condition checks.  SAZ and
   SNZ permit the accumulator to be checked for zero or non-zero
   contents.  SAG and SNA enable any bit position in the accumulator to
   be checked for a 1 or 0 setting.  SNO provides a check for
   accumulator overflow.

                        Input/Output - SS, DIN, DOT

   The SS instruction provides a means of determining whether devices
   which interface with the processor (e.g., modem display module) are
   ready for data transfers.  Actual transfer of data occurs through the
   accumulator, one word at a time.  DIN causes one 16-bit word to be
   transferred from an external device to the accumulator.  DOT
   indicates the transfer of one 16-bit word from the accumulator to an
   external device.  The particular device DIN or DOT address is
   indicated by the value in the device address field of the
   instruction; the instructions enable controller I/O with a variety of
   peripheral units.

                          Jump Control - JMP, JSR

   These instructions provide the means for altering the flow of program
   logic.  JMP is an unconditional transfer of control to a designated
   memory location.  JSR provides a subroutine capability to the
   program.  The execution of a JSR instruction involves saving the
   return address to the jump at a designated location.  By designating
   the store for the return address as not being in line with executed
   code, the program which is in execution can be held in read only
   memory.

                              Indexing - IAS



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   These instructions provide an indexing facility to the order code.
   The indexing occurs in the memory location specified in the address
   field of the IAS instruction; thus, multiple indexing is possible.

   The above instruction types provide a fundamental but general
   programming capability.  A basic symbolic assembly language has been
   built about this instruction set and is used to write programs which
   do character, assembler program; the assembler is written in FORTRAN
   language.

   Modem

   The display terminal is supplied with a modem for interfacing the I/O
   controller with a telephone line.  The modem operates asynchronously
   through one of the three I/O controller ports (Figure 5).  It is an
   FSK unit that operates at data rates from 0 to 1800 bps in a four
   wire full-duplex mode and from 0 to 1200 bps in a half-duplex mode.
   In the four wire full-duplex mode, both the local and remote modem
   operate fully independently.  A data transfer sequence may be
   originated from either model at any time by activating the Request To
   Send signal.  The data transfer sequence is terminated by dropping
   the RTS signal at the originating modem.  In the half-duplex mode,
   the modem operates with any data format.  Selection between transmit
   and receive modem identity is determined by the status of the Request
   To Send signal from the processor.

   The modem may be used over a dial-up network using the half-duplex
   mode.  Operation in this manner requires the use of the November,
   1968, Data Access Arrangement, number F-57951, supplied by the Bell
   System.  In this operating mode, a data call is originated by the
   phone set associated with the Data Access Arrangement.  At the remote
   location, the call is manually answered and the data key on the phone
   se is placed in the data position.

   Keyboard

   A multimode keyboard with standard ASCII character-to-key assignments
   is proposed.  The keyboard includes codes for upper and lower case
   alphanumerics and special function keys and codes for editing
   operations.

   [Figure 5 DS-1 I/O Data Lines*]

   Section 4 Mechanical Considerations

   The DS-1 consists of three separate self-contained sub-units: the
   display module, the processor module, and the keyboard.




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   Display Module - The Display Module will contain the plasma panel and
   the driver electronics.  It's overall size will 14" W x 14" H x 61/2"
   D, and will weight approximately 25 pounds.  An 8-1/2" x 8-1/2"
   viewing area will be provided.

   Interconnections to this unit will be provided at the rear of the
   assembly.

   Processor Module - The processor enclosure will contain circuit board
   assemblies, three separate power supplies, and a cassette tape
   recorder (optional).  The overall size of this unit will be
   approximately 20" W x 6-1/2" H x 26" D and will weigh approximately
   60 pounds.

   Input/Output connectors will be provided at the rear of the enclosure
   to accommodate the units with which it must interface.

   Keyboard - This unit will provide a full alphanumeric keyboard housed
   in a desk top enclosure approximately 15" W x 3" H x 7" D.  The unit
   will include:

   o  The entire displayable character set in the standard ASCII layout.

   o  Special Function keys for editing and I/O control.

   Keyboard operation is similar in touch characteristics to an electric
   typewriter and suitable for use by an inexperienced operator.

   Appendix I

   DS-1 Instruction Set The following instructions are provided;

   The execution item for instructions having indirect addressing
   (optional with instruction marked*) requires one cycle for each
   indirect level.

   LDA, A, I Load Word      0  1  2  3  4      15
                            I  0  0  0      A

   This instruction loads the contents of address A into the
   accumulator.  The previous contents are lost.  The program counter is
   indexed by 1.

                              Time = 1 cycle*
                            0  1  2  3  4      15
   JMP, A, I, Jump          I  0  0  1      A





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   This instruction causes program control to be transferred to the
   address A.  The contents of the accumulator are not altered.

                              Time = 1 cycle*
                            0  1  2  3  4      15
   JSR, A, I, Jump & Save   I  0  1  1      A
                   Return

   This instruction stores the present address plus 1 at the location
   specified by the contents of memory location A and transfers program
   control to location A+1.  The accumulator is cleared.

                              Time = 3 cycles*
                            0  1  2  3  4      15
   ADD, A, I, Add           I  0  1  0      A

   This instruction adds the contents of memory at location A to the
   accumulator.  The overflow indicator is set to the appropriate state
   and remains set until the next ADD, IAS, or CLA instruction is
   processed.

                              Time = 2 cycles*
                            0  1  2  3  4      15
   AND, A, I And            I  1  0  0      A

   The instruction ands logically the contents of the accumulator with
   the data stored in Location A.  The results is stored in the
   accumulator.

                              Time = 2 cycles*
                            0  1  2  3  4      15
   STA, A, I Store          I  1  0  1      A
           Accumulator

   This instruction stores the contents of the accumulator in memory
   Location A.

                              Time = 2 cycles*
   IAS, A, I Index & Skip   0  1  2  3  4      15
             If Zero        I  1  1  0      A

   This instruction reads the contents of memory location A and adds 1
   to it.  The results are then stored back in location A of the memory.
   If the results of the addition is zero (i.e., an overflow generated)
   the next instruction is skipped.  Otherwise, the next instruction is
   executed.  The accumulator contains the contents of A plus 1.





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                              Time = 3 cycles*
                            0  1  2  3  4  5  6  7  8   11  12  15
   SAL, N Shift             0  1  1  1  0  0  0  0    n
   Accumulator Left

   This instruction shifts the contents of the accumulator left by n
   bits, the least significant bits become zero.

                              Time = 1 cycle*
                            0  1  2  3  4  5  6  7  8   11  12  15
   RAL, N Rotate            1  1  1  1  0  0  0  0    n
   Accumulator Left

   This instruction rotates the contents of the accumulator left by n
   bits.  The most significant bit becomes the initial least significant
   bit.

                              Time = cycle*
                            0  1  2  3  4  5  6  7  8    15
   HLT, Halt                0  1  1  1  1  0  0  1

   This instruction causes program execution to stop.  Used primarily
   for debugging purposes, depression of the RUN button or SINGLE CYCLE
   button causes continued execution either continuous or one cycle
   respectively.

                              Time = 1 cycle*
                            0  1  2  3  4  5  6  7  8    15
   SAZ Skip Accumulator     0  1  1  1  0  1  0  0
   Zero

   This instruction causes the next instruction to be skipped if the
   accumulator is zero.

                              Time = 1 cycle*
                            0  1  2  3  4  5  6  7  8    15
   SNZ Skip Accumulator     1  1  1  1  0  1  0  0
   Non-Zero

   This instruction causes the next instruction to be skipped if the
   accumulator is non-zero.

                              Time = 1 cycle*
                            0  1  2  3  4  5  6  7  8  11  12  15
   SAC, B Skip              1  1  1  1  0  1  0  1    B
   Accumulator





Liddle                                                         [Page 15]
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RFC 296                   DS-1 Display System               January 1972


   This instruction causes the next instruction to be skipped if bit
   number B is one (1).  The most significant bit is zero and the least
   significant is 15.

                              Time = 1 cycle*
                            0  1  2  3  4  5  6  7  8    15
   SNO Skip No                 1  1  1  0  0  0  0
   Overflow

   This instruction causes the skipping of the next instruction if the
   overflow is not set.

                              Time = 1 cycle*
                            0  1  2  3  4  5  6  7  8    15
   CMP Complement              1  1  1  0  0  1  1
   Accumulator

   This instruction stores the 2's complement of the accumulator in the
   accumulator.

                              Time = 1 cycle*
                            0  1  2  3  4  5  6  7  8  11  12  15
   DOT Data Output             1  1  1  0  0  0  1   Add    Func.

   This instruction causes the contents of the accumulator to be gated
   to the DIO Data buss and a Data Output Strobe (DOS) pulse to be
   transmitted to the peripheral device.  This pulse is used by the
   device to store the contents of the Standard I/O Buss.  The device
   Address and Function data is transmitted simultaneous with data.

                              Time = 1 cycle*
                            0  1  2  3  4  5  6  7  8  11  12  15
   DIN Data Input              1  1  1  1  1  0  0   Add    Func.

   This instruction causes the device address and function data to be
   transmitted as in the DOT instruction.  Upon detection of this
   address, function and DATA Input Strobe (DIS), the device gates its
   data onto the Standard I/O Buss.  The deactivation of the Data Input
   Strobe indicates that the data has been received and stored.

                              Time = 1 cycle*
                    0  1  2  3  4  5  6  7  8  9  10  11  13  14  15
   INR Interrupt    0  1  1  1  1  1  1  1  0  0   0     L    0    0
   Return







Liddle                                                         [Page 16]
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RFC 296                   DS-1 Display System               January 1972


   This instruction causes the Program Counter, the Accumulator, and the
   Overflow indicator to be restored to the conditions prior to
   servicing the present active level.  Parameter L must be set to the
   level being processed for correct return linkage.  The interrupt is
   returned to the idle state.  See pages 3-3 and 3-4.

                              Time = 4 cycles*
                            0  1  2  3  4  5  6  7  8    15
   MSK Mask Interrupts      1  1  1  1  1  1  1  0

   This instruction causes the interrupt system to be inhibited from
   causing any interrupt to be processed.  Interrupts waiting or
   received while interrupts are _masked_ will be processed when they
   are unmasked.  See pages 3-3 and 3-4.

                              Time = 1 cycle*
                            0  1  2  3  4  5  6  7  8    15
   UNM Unmask Interrupts    0  1  1  1  1  1  1  0

   This instruction causes the interrupt system to be processed in the
   normal manner.  See pages 3-3 and 3-4.

                            Time = 1 cycle*

   * Please see the PDF file for figures and missing text (not legible in
     the original).

























Liddle                                                         [Page 17]
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