The SEQUEL software language

EU ROM ICRO Journal 4 (1978) 30-38 © EU ROM ICRO and North-Holland Publishing Company

The SEQUEL software language Colin Dye Hawker Siddeley Dynamics Engineering Ltd., Hatfield, UK

Synopsis

SEQUEL is a microprocessor based

sequencer controller for control and mon-

itoring operations in industry. It is

designed to be modular in both hardware

and software so that construction, use

and maintenance of the equipment Can be

achieved by plant engineers.

The hardware is based upon double euro-

card size circuit boards contained within

a standard rack system. The range of

boards available comprises CPU, two types

of memory, digital input and output

boards, analogue input and output boards

etc.

A special easy to learn programming language, called SEQUEL, has been devised

to enable the control requirements to be

entered into the system by the plant

engineer. The system does not depend

upon a host computer or specialist programming knowledge for its operation.

Full simulation features as well as all

aids necessary to prepare programmes are

included with the supplied software so

that engineers can write and test their

programmes fully before coupling up to

the plant to be controlled.

i. INTRODUCTION

As a prelude to describing the SEQUEL

system software it may be of interest to briefly explain the origins of the SEQUEL

project. The design and construction

of the SEQUEL hardware will then be des-

cribed as the SEQUEL language, and its facilities are intimately tied to the hardware.

SEQUEL arose from a requirement by the Central Electricity Generating Board

(CEGB) for an electronic sequence con-

troller for equipment in one of the new

power stations. Hawker Siddeley

Dynamics Engineering Limited has been in-

volved in microprocessors almost since

their inception on other control equip-

ment and decided to use a microprocessor

to satisfy this requirement. It was

reasoned that the microprocessor would

give a high degree of flexibility for the

controller, as well as cost reductions

and increased reliability. The design

was well under way when the project was

cancelled due to the rise in fuel

prices coupled with a falling demand for

electricity. The Company decided that

the concept of the sequential controller

was sound, would be a viable new product

and decided to press ahead with its

development as a Company-funded venture.

The development guidelines were widened

to expand the system into a general-pur-

pose sequence controller for the indust-

rial market.

2. DESIGN CONCEPTS

The design brief for the hardware and

software engineers was to design a system that was -

(i) Simple

it should not require a

qualified programmer to programme the system, or

a qualified electronics

expert to put it together

(ii) Easy-to-use

the equipment was to be aimed at the plant engineer or production man. He is the one who

30

THE SEQUEL SOFTWARE LANGUAGE 31

(iii)

(iv)

understands his problem

and the system should enable

him to easily solve his

problem without expensive,

long training or recourse

to the controller man-

ufacturer

Flexible

the basic building 'bricks',

both hardware and software,

of the system should be

as flexible and as multi-

purpose as possible, with-

out any compromise over

performance

Modular

(vii)

Conditions encountered

are often harsh, hot, dusty,

vibrations from other

machines, electrical inter-

ference etc., and the system

must be designed accordingly

Low Cost

this almost goes without

saying. The advantages

of using microprocessors

must be passed on in a

competitive price. The

total SEQUEL concept, es-

pecially the price, must

make the system attractive

to a wide variety of users

(v)

(vi)

the equipment should

comprise plug-in components

with easy connection be-

tween the modules. The

software also should be

designed on the 'Lego'

principle to allow for

easy additions and amendments to the system

Ease of Maintenance

an almost automatic by-

product of the modular

concept is ease of main-

tenance. Replacement

of the hardware was to be

reduced to a board re-

placement level. In

software terms the use of

software modules means

easier testing and debug

at the programme develop-

ment stage, and quicker

fault-finding sub-

sequently

Robust Construction

the system should be

capable of operating where

it is needed; on the plant. No special en-

closures should be required and it certainly

should not require a computer room environment.

Fig. 1

3. HARDWARE

POWER SUPPLY AND

CARD FRAME

32 C. DYE

The Power Supply is rack-mounted and

supplies all the necessary logic vol- tages with extra supplies for the relay

cards and front panel displays. The

supply has a power-fail detection system

which, in conjunction with SEQUEL soft-

ware, enables the system to cope with

mains interruptions and failures and

protects the memory from corruption.

The Card Rack is a simple 19" double

eurocard rack, with a backplane buss

structure. This enables any module to

be plugged into any position in the rack

aiding assembly and maintenance.

Fig. THE PROCESSOR CARD

The SEQUEL system utilizes the

ubiquitous Intel 8080. It features

three serial interfaces for current loop,

V24 and modem devices driven by a USART:

programmable baud rate and clock rate

counters, power-fail logic in conjunction

with the Power Supply and a bootstrap ROM

for initial programme loading.

Fig. 3 MEMORY MODULES

Two types of memory module are shown in

Fig. (iii), the 8K Core Store and the PROM/RAM board.

Core memory is used for development of SEQUEL control programmes and when the event-log facility is required. PROM/

RAM is used when absolute programme security is required. In practice we

have found the core stores to be virt-

ually incorruptable.


The analogue output board has four

channels per board. Each output has 12

bits resolution and provides a physical

output of plus or minus ten volts or

+_ 20mA. The output can be updated as of-

ten as required by the programme.

In addition to these boards others are

currently under design or the subject of

ongoing research and development.

From the foregoing it can be seen how the

design criteria has been met with regard

to the hardware. The system builds up

in the 'Lego' manner and expansion is

merely a question of adding more modules and racks as necessary. Future develop-

ments will follow the existing construction

principles and be fully compatible with

the current range of modules.

Fig. 4 DIGITAL INPUT AND OUTPUT BOARDS

There is a range of digital input and

output boards as shown in Fig. (iv).

They come in two variations.

16-way isolated input and output boards,

where each input or output is isolated

from each other and from ground. These

boards are used to connect to or from

the plant.

32-way non-isolated input and output

boards. This type of interface is used

mainly to connect to and from control

panels and to drive displays.

In addition, there are analogue input

and output boards.

The analogue input is driven through a

32-channel multiplexer board. Up to

four multiplexers may be attached to any

one A-D board giving 128 channels per

A-D. The A-D itself is the integrating type giving l!-bit resolution plus sign

with seven programme selectable input

ranges and overload detection.

3. SOFTWARE

Now how have the original design con-

cepts been implemented in software?

The requirement for simplicity and ease

of use precluded the use of assembly lan-

guage as the programming language. The

system must be capable of being program-

med by a user with the minimum of

training. In our view the typical user

will not be trained in programming, and

rightly so, and need not even have an

appreciation of the operation of computers.

We could utilise one of the ~stablished

high-level languages but these are

generally large in core usage, and often

require the use of a disc drive for

compilation. The use of a disc drive

would make the cost of the system unac-

ceptably high, and would certainly rule

out the use of the equipment in adverse

environments. Also considered was the use of an interpretive language, such as

Basic, but it was soon realised that such

a language did not fit in with the

original design aim and would not execute

fast enough. It was therefore decided

to design our own language.

Fig. (v) shows a typical control require-

ment.

34 C. DYE

L,~,,

SEQUEL PROGRAMMABLE

CC~('fFIR OLLE R

co.,.o, ,,.c~ 0,,,~*,,-

Fig. 5 TYPICAL CONTROL CONFIGURATION

The controller accepts information from

the plant in various formats, it inter- prets the pattern of signals received and

sends control information back to the

plant, based upon the received data. To

perform the control function we must be

able to uniquely indentify any signal to

or from the plant, and be able to refer-

ence these signals from within the pro-

gramme. To achieve this any individual

plant signal to or from the plant is

called a Line.

Because an 8-bit microprocessor is used

these Lines are referenced in groups of

eight, which are called Ports. Thus,

any digital signal to or from the plant

can be uniquely identified by its Port

and Line number. These digital signals

may be in one of two states, either ON

or OFF, usually denoted by a 1 or an 0.

This 0 or 1 state is called the condition.

We now have a means to reference any

signal to or from the plant, and to test

or to set its condition. This plant

connection referencing system is the base

from which the language is constructed.

Each individual action that the controller is to perform is defined by one pro-

gramme instruction. Every instruction

must have an 'instruction identifier'

somewhere so that programme action can

be followed and programme changes can be

easily made. A means must be devised

to indicate the type of action to be performed by the instruction: and also a means to tie that action to a particu-

lar plant connection.

Here is a typical SEQUEL instruction -

735 TLI 3,5,1 IS VALVE CLOSED?

First, is the 'instruction identifier'

or statement number which uniquely

identifies the instruction. The state-

ment number can be regarded as a 'label'

to the instruction. It is referenced by

other SEQUEL instructions to transfer con-

trol within a programme and by the various programme testing aids, simulation, pro-

gramme monitor panel etc. to indicate the

position of the programme.

Next comes a three-letter mnemonic field

which defines the action to be performed.

In this case, TLI means ~est Line. All

SEQUEL mnemonics are indicative of the

action to be performed, helping to make

them easily memorised.

Following the mnemonic field is the argu-

ment field. This contains information

which, when taken in conjunction with the

mnemonic field, defines precisely the

operation to be performed.

In this case, the action is to test Port

3, Line 5 for the condition one, (or 'on'

Lastly, comes a comment field, which is

used by the programme writer to describe

his prograntme as he sees fit.

S E Q U E L M N E M O N I C S

P L A N T C O N D I T I O N S

T L I - - T E S T O N E

OLI - - O U T P U T LINE

T P T TEST PORT

O P T - - O U T P U T PORT

p R O G R A M C O N T ! : E ) L J M p - - UNCONOIT rONAL JUM~

JEQ J U M P IF EQUAL

j , '~E - - . J U M ~ IF N O T EQUAL

j G T - - j U M p ?F GREATER THAN

J L T - - J U M P IF" LESS THAN

T I M E R S

R E G I S T E R S

M E S S A G E

S T I - - S T A R T T~MER

C T [ COMPARE T IMER

ip R ~ INPUT PORt T O REGISTER

ORP O U T P U T PEGISTER TO PORT

PEQ -- REGISTER ESTATE

I E INCREMENT REGISTER

DEC - - DECREMENT REGISTER

ADD ADD REGISTERS

SUB - - SLr~TRACT REGISTERS

A N D - - L jOGEAL ANO REGISTERS O ~ R LOGICAL OR R E G I S T E R S

XO R -- LOGICAL EXCLUSWE OR REGISTERS

SL L - - SHIFT LEFT LOGICAL SRL SHIFT RIGHT LOGfCAL

MQV - - MOV E ~EGI~TER TO REGISTER

ERR - - COMPARE REGISTER TO REGISTER

CRG COMPARE REGISTE~ T O LITERAL

PRT - -

SEQUEl_ INTERLOCKS

ASQ -- ACTIVATE SEQUENCE

O S Q - - D E A C T I V A T E S E Q U E N C E

O S Q - - O V E R R I D E SEQUENCE

C S N - - C O M P A R E S T A T E M E N T N U M B E R

Fig. 6 SEQUEL MNEMOniCS


Using this structure we built up a range

of instructions for all the actions that

we wished the controller to perform.

Fig. (vi) gives a list of all the basic

SEQUEL mnemonics, or instructions.

In later versions of the software, the

register capability of the system has

been enhanced to allow the use of floating

point numbers, thus greatly increasing the

tasks that this system is capable of

performing.

The first four instructions are used to

test or set plant conditions. The TLI

and OLI instructions operate on individ-

ual lines, whilst the TPT and OPT in-

struction is used to test lines in groups

of eight. This can be very useful when

searching for a particular combination

of plant conditions. A refinement of

the Port instructions is the use of X

in the argument field to denote 'don't

care', i.e.

830 TPT 6,01XXI011

This allows us to test from 2 to 8 lines

for any desired simultaneous combination.

The next five instructions are used to

transfer programme control within the

programme. Their argument fields are

the statement numbers of other instruc-

tions. They are used following a test

type instruction, so that programme

action can be made conditional upon the

result of that test.

All plant controllers require timing fun-

ctions to set delays or to time events.

The two Timer instructions allow Timers

to be started and tested at any subsequ-

ent point within the programme. Within

SEQUEL, a 24-hour clock is maintained so

that delays of up to 24 hours can be made

with a resolution of i0 milliseconds.

The CTI instruction can be used as often

as required so that multiple events can

be timed from one timer.

The Print instruction allows messages to

be displayed on any suitable terminal

device. These messages may be instruc-

tions to an operator, test results, or

whatever. The contents of registers as

well as time and date can be printed.

The use of this facility allows quite

sophisticated displays to be constructed

as well as just simple messages.

So far the SEQUEL language and its inst-

ructions have been treated as if it were

one long sequential programme. It was

decided early on in the software design

that the system must be capable of mon-

itoring several plant conditions simul-

taneously. With only one programme in

the machine it is more than likely that

the controller may be performing actions

defined by one part of the programme and

completely miss an important occurrence

on the plant because it is not at the

relevant part of the programme.

This problem was overcome by the use of

Sequences.

Any plant control programme can be

broken down into a number of self-con-

tained functions or tasks. Thgse tasks

are called Sequences. Each sequence

can be allocated to perform a definite

plant function, such as 'start motor'

or 'check lubricating oil circuit', etc.

An important feature of SEQUEL is that

sequences are run in parallel. Fig.(vii)

shows this feature diagramatically.

Within the system are areas in which data

may be stored and manipulated. These

areas are called Registers, and like

ports they are eight lines, or bits, wide.

Data can be read to or from the ports

into these registers, or they may be

loaded with data from within the program-

me. As well as manipulating what is in

effect port data in the registers, we can

also do simple integer arithmetic and logic functions.

SEQUENCE I

Fig. 7

SEQUENCE 2 SEQUENCE 3

~0 TLI ~.29 . . . . . . . . SO,EQ 2 ~ . . . . . . . 3'~0 S!L4

~ L 1 6 7 . 1 . . . . . . . 7 0 IPR 6.5 . . . . 4 0 5 JL3 2 . 0

l l SIMULTANEOUS INSTRUCTIONS

36 C. DYE

Only three sequences are shown as active,

but the dotted line shows the flow of

control taken by the processor. It can

be seen that while each sequence progres-

ses down through its own task, the SEQUEL

software ensures that only one instruc-

tion from any one sequence is processed

before moving control to the next sequ-

ence. Thus, the system is able to per-

form concurrent tasks and these tasks

need bear no relationship to each other.

modifications to be easily made by

copying a programme from one cassette to

another, inserting or deleting programme

instructions as required. A search

facility on the terminal allows a search

at high speed for a particular statement

number to be made speeding up the editing

process. New programmes can be typed up onto cassette and edited completely

off-line from the controller without tie- ing up the machine.

This feature is very useful when provid-

ing a 'safety monitor' type function for

a plant, as the monitoring can be con-

tinuous irrespective of the control as-

pects of the plant.

5. SUPPLIED SOFTWARE

SEQUEL systems are supplied with three system programmes -

Parallel sequences are used to provide

interlocking of plant functions and a

range of mnemonics are available to con-

trol this.

ASQ and DSQ activate and de-activate

sequences respectively. (see SEQUEL

INTERLOCKS - Fig. (vi).

A de-activated sequence has no effect on

the plant. Override sequence, OSQ, and

compare statement number, CSN, are used

to monitor and override any one sequence

from any other sequence.

The objective in designing SEQUEL is

that it must be simple and easy to use.

The modular nature of the hardware means

that physically the system can be easily put together. On the software side,

the programme instructions are simple,

and easy to learn, but the user must

have a means to easily input his instruc-

tions to the machine, and test that his

progra~ne will function correctly. He

should also be able to make programme

changes and modifications quickly and

readily.

4. TERMINALS

For simplicity, it was decided to use a proprietary terminal to construct and

edit programmes. The system is able to use a variety of terminals, including

the ubiquitous Teletype, but the Texas Instruments Silent 700 is preferred. The

twin cassette facility allows programme

The Executive

This programme is permanently resident in

the machine. It is initially loaded by

pressing an Executive Programme Load

button on the control panel, which acti-

vates a bootstrap ROM on the CPU board.

Once in, the programme need only be re-

loaded in the event of a memory failure.

For systems with PROM/RAM memory this

programme will be already present in the PROM.

The Executive provides basic 'house- keeping' facilities for the SEQUEL system,

(i) Real-Time Clock

A 24-hour clock is maintained

which can be set or displayed at any time. The clock reso-

lution is i0 msecs. A cal- endar facility is also in-

cluded, geared to the real-

time clock.

(ii) Power-Fail Management

The power supply indicates to the processor the onset of

power failure. Software is

provided for an orderly shut- down of programme activity.

When power is restored, the

system is able to restart

where it left off if required. This feature guards against

memory corruption due to

supply fluctuations.


iii)

(iv)

(v)

Health Monitor

Every clock pulse the system

retriggers an indicator on

the CPU board. If for any

reason, hardware or software,

the system fails to retrigger

the lamp it goes out, in-

dicating a system failure.

Communications

The system is able to talk to

a variety of terminal devices,

or other processors, through

any one of the three inter-

faces on the front of the

CPU board. Input and out-

put are interrupt driven

into and out of separate

buffers.

Tape Handling Facilities

Software is provided to

drive remotely the $700

terminal. Each cassette

unit can be commanded

individually to Rewind,

Load, Playback or Record.

The user just needs to ask

the system to Read or Write

a particular tape and the

system does the rest.

In addition, the Executive holds common

sub-routines which are used by the

Translator or Interpreter programme.

The system will only allow an error-

free control programme to be run, so the

user is forced to correct all errors.

Once an error-free programme is obtained,

the Write facility of the Executive can

be used to obtain a machine code copy of

the programme onto a cassette. Subsequ-

ently, if this particular control program-

me is required, it can be quickly loaded

into the system in machine code form

without having to perform a re-Trans-

lation.

The Interpreter

The interpreter takes the machine code

SEQUEL instructions and applies them to

the plant. It contains all the software

necessary for the simultaneous processing

of sequences, the timers, registers, etc.

To aid in programme development some use-

ful features have been built into the

Interpreter.

(a) Programme Monitor Panel

The use of this panel allows

the progress of any sequence

to be monitored. The desired

sequence number can be called

up and the corresponding

statement number within that

sequence will be displayed.

In addition any sequence may

be started or held at any

statement within that sequ-

ence by use of push buttons.

(b) Simulation

The Translator

This programme and the Interpreter both

occupy the same area in memory, and are

thus mutually exclusive. The Translator

is read into the system by the Executive.

Its job is to read through the control

programme, written in the SEQUEL lan-

guage, and convert it to machine code.

Simultaneously, it will produce a paged

listing of the programme for record pur-

poses, and indicate any syntax or logic

errors. The user must correct any pro-

gramme errors by using the edit facilit-

ies of the Terminal.

This allows the programme to

be completely debugged with-

out the need to be connected

to the plant to be controlled

In simulation mode the Inter-

preter displays the sequence

and statement number of every

instruction as it is being

performed. When an instruc-

tion requires a plant condit-

ion i.e. a TLI instruction,

the system asks the operator

to enter the condition, it

does not reference the plant.

Similarly, if an instruction

is encountered which will

C. DYE 38

change a plant condition,

the change is displayed to

the operator, rather than

being sent to the plant. A

sample print-out of the

simulation mode is shown

in Fig. (viii).

-START l.lO SEQUENCE N~:01.STATEMENT NUMBER:00010 OE~O pRC~RA~ SEQUENCE NO:01.STATEMENT NUMBS:00020 ~N ON SWITCH 1 SE~ENCE NO:OI.STAT~E~ ~MB~R:00030 INPUT PORT:015.pREV~OUS STATUS:O0000000.CURRENT STATUS:?0000000 SEQUENCE NO:01.STATEMENT NUMgSR:O0040 SEQUENCE NO:02.STATKME~NT ~.~M~SR:000[0 SEQUENCE NQ~OI.STAT~MENT NUMBER:00050 OUTPUT PORT:015.pREVIOUS STATUS:OIO]OIOI.CURRENT STATUS:J0101010 SEQUENCF. NO:02. STATEMENT N~MBF.R:O0020 SEQUENCE NO:01. STATEMENT NUMSE~ :00060 OUTPUT PORT:016.PREVIOUS STATUS:01010101.CURRENT STATU5:IOIOI01) SEQUENCE NO:02.STATEMENT N"OMB£R:00030 SEQUENCE NO:01.STATEMENT STATUS:00070 SEQUENCE NO:O2.STATKMENT hq/MBER:0004O SEQUENCE NO:OI.STAT~MKN~ NUMBER:000@0 SEQUENCE NO:02.STATF24ENT NUMBER:O0050 SEQUENCE NO:04.STATF~SNT N~M,ER:000[O SEQUENCE NO:02.STATKMENT NUMBER:00060 SEQUENCe NO:O4.STATEMENT NL~I~R:00020 OUTPUT PORT:OI5.PR~VIOUS ZTA?US:I01OI010.CL~RENT STATUS:r~I0101CI

Thus, the user is able to

completely test his pro-

gramme, trying all con-

ceivable combinations of

plant conditions and

verifying that the desired

response is made before

connection to the plant.

The usefulness of this

feature is self-evident,

especially when very

expensive plant is involved.

The Interpreter also allows

the status of registers to

be displayed and changed

at any time. The condition of any Ports may also be

interrogated and individual

Lines may be overridden to

be on or off as desired to

overcome any plant mal-

function.

6. THE FUTURE

This then is what SEQUEL is and how it has developed so far. What of the

future?

The system is in a constant process of

evolution, and the use of the micro-

processor in the system is crucial to

its flexibility. The advances in

microprocessor technology allow us to

build sophisticated interface boards at

low cost. For instance, we have al-

ready built A to D and D to A boards and

we are currently building counter/timer,

stepper motor drive and SDLC link distri-

buted control hoards as well as investi- gating further facilities.

On the software side, the use that can

be made of these boards and the facilities

that can be built into the language seem

almost endless. Already floating point

mathematics and analogue capability are

offered. Shortly three-term control

and data logging will be available. Soft-

ware will also be available for the new

boards as and when they arrive. Distri- buted control is a new and expanding

field and the subject is being followed

closely.

The advent of microprocessors has meant

that we are able to produce a flexible,

simple, powerful industrial controller

with the capability to satisfy most

industrial control problems at a reason-

able cost. Our experience has shown

that new users of SEQUEL are able to use

the equipment effectively to solve their

control problems within a matter of

days. We already have systems in the

field with over a years continuous

operation and the interest shown by

industry leads us to believe that this

equipment is the answer to many control

problems.

Documents

The SEQUEL software language