© EUROMICRO EUROMICRO Journal 6 (1980) 24-27

IMP 2000, an Industrial Microprocessor

K. Clausen BUHL AUTOMATIC,Topstykket 24, DK-3460 Birkered, Denmark

Today's complex and highly specialized control schemes for industrial machinery combined with simple operation and fast set-up and adjustment procedures are conveniently realized with mod- ern microprocessor technology. The easy implementation of special control features presented by software programmable systems offers advantages to the user as well as to the manufacturer of control systems by minimizing hardware complexity thereby increasing reliability. The fol- lowing is a presentation of the hardware- and software configuration of the system SPS (Soft- ware Programmable System), a general multiprocessor control system for industrial purpose. An application example is examined - the IMP 2000, which is a dual processor control unit. Special emphasis is laid on the I/O subsystem based on a CMOS external bus architecture.

1. COMPANY BACKGROUND

BUHL AUTOMATIC was founded in 1958 as a produc- t ion company in indust r ia l control . During these 20 years the control systems developed, manufac- tured and marketed by BUHL AUTOMATIC have under- gone a ver i tab le revolut ion s tar t ing with simple sequential controls based on relay techniques. In sh i f t ing to discrete e lectronic components and gradual ly introducing IC-logic component fami l ies as DTL and TTL the cont ro l l ing capabi l- i t y was enhanced with more complex logic func- t ions (d ig i t a l pre-settable timers) and analog functions (analog control of hydraulic valves and measurement of posit ions and hydraulic pres- sure).

In the ear ly seventies the CMOS logic fami ly with i ts high noise immunity and low power con- sumption presented an LSI component family very well sui table to handle logic control functions in noisy indust r ia l environments. Along with the introduct ion of closed loop control of hydraulic systems the CMOS offered a simple way of gener- ating complex pro f i les for time- as well as po- s i t ion dePendent references for pressures and ve loc i t ies .

Now, why scratch the well known conventional concept developed during several years to a pow- erful versat i le system of control modules eas i ly combined to a special ized control unit? The most obvious drawback of the conventional system is that by i t s nature i t is hardwired programmed. One module takes care of one special funct ion. As the v e r s a t i l i t y of the system grows, the amount of hardware grows. Though hardware prices are dropping the amount of necessary hardware is growing in a higher rate so that the f inal , price is actua l ly growing. And more seriously - the complexity of c i r cu i t r y grows causing a r e l i a - b i l i t y drop of the equipment. As a consequence of these aspects a software programmable micro- processor-based system has proved to be a com-

pe t i t i ve technology for future development. The bus-oriented architecture is well suitable to carry on the t rad i t i on for module based systems in the hardware as in the software. Therefore i t combines the r e l i a b i l i t y of r e l a t i v e l y few stan- dard hardware modules with the v e r s a t i l i t y of software programming.

2. IMP 2000 SYSTEM CONFIGURATION

The IMP 2000 presents an appl icat ion example of the SPS system conf igurat ion. The SPS system is a multi-CPU system with from one to four CPUs of Intel 8085 type. The CPUs are combined into one system via a communication l ink which actua l ly is a common RAM area containing a l l data that must be accessed from more than one CPU. These data are:

- temporary data communicated among the various CPUs,

- the handshake type data which controls the communication, and

- the set of data characteristic to the con- trol led process (process parameters).

This last group has a permanent nature, and to save them in power-down situations (during week- ends) the "common RAM" is made in CMOS technol- ogy with battery back-up.

Around the common RAM the CPUs are arranged. In the IMP 2000 two CPUs are supplied as standard, one essentially communicating with the process (controll ing the process-interface) and the other essentially communicating with the operator (con- t ro l l ing the console system). This configuration is i l lustrated in Fig. I.

3. CPU MODULE

The CPU module is a self-contained microcomputer with on board ROM, RAM, and t imer -c i r cu i t as well as b id i rec t iona l bus drivers for extending the

24

K. Clausen 25

F

C O N , 9 0 L It J

Fig. 1. SPS System Configuration.

CPU bus to other modules. The 64k memory space of the 8085 is al located as fol lows:

- 32k of ROM of which 16k is avai lable when using the 2k by 8 PROM type. I f needed the 4k by 8 PROM type can be supplied extending the program area to 32k.

- 4k of scratch-pad RAM for processing; - 8k of common RAM for communication to the

other CPUs; - 13k of RAM area divided into lk sections each

of which can be al located to peripheral de- vices, one by one or a r b i t r a r i l y col lected in groups as required. The remaining 7k of memory space is not avai lab le but is par t ly used for the control of the on board timer and I /0 c i r - cu i t .

4. I /0 SUBSYSTEM - EXTERNAL BUS

The most in terest ing peripheral device in the indust r ia l context is the process inter face. The process inter face is the l ink that t ies together the processor and the process contro l led. To do this properly for a great many processes the I /0 subsystem must

- comprise a wide var ie ty of signal condit ioning modules to control machine power and measure events,

- provide a transmission l ink between real world and the processor,

- guarantee e f f i c i e n t noise reduction, and - provide error detect ing/correct ing capab i l i t y .

To meet these demands and yet keep the system manageable one should keep in mind some optim- iz ing considerations:

- signal condit ioning modules share common ele- ments where possible to minimize hardware costs;

- processor-dependent interface logic not on signal conditioning modules to minimize hard- ware complexity;

- CMOS logic to reduce noise sens i t i v i t y and power consumption;

- memory mapped I /0 ; - no need for in ter rupt -dr iven A/D conversion.

The answer given in the IMP 2000 is the EXTERNAL BUS shown in Fig. 2. The external bus is real ized in CMOS technology and is en t i re l y control led by the bus-interface module (BIF). I t mult iplexes a l l input and output via the same set of opto- iso lators on the BIF. On one hand this saves op- to - i so la to rs , on the other hand i t provides iso- la t ion of a l l input-output including A/D -con- verters.

The operation of the external bus is transparent to the CPU and vice versa making the I /0 t rue ly memory mapped.

The updating rate of the mul t ip lexing is approx- imately one cycle per ms. This means that when- ever the CPU needs an input value i t gets a val- ue which has been updated within the las t m i l l i - second. I t also means that i f e lec t r i ca l noise succeeds to switch an output, th is output w i l l be re-establ ished within i ms.

5. PRIMARY SECURITY

Two d ig i ta l input modules have CMOS logical out- puts which d i rec t l y re f l ec t the state of the corresponding input signal. Likewise the output modules have CMOS inputs, which block the active state of the i r corresponding outputs when held in high state. This provides for primary securi ty (personal securi ty) which according to author i ty demands must be made as d i rec t l y as possible, i . e . , independent of software.

I t is in terest ing to notice that this f a c i l i t y also enables the user to do some (simple) pro- gramming by wiring the rack.

6. SELF-CHECK

The IMP 2000 has a detai led self-check scheme. I t

J[ CPU'/~us eomp~ti61e ~u//ree aee~ I

1F .u, I optoooupter .pa.,.i°. I

Ir JL I eMos .,,,.,,,~,lZ.,s~o,,t,ot I

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Fig. 2. SPS Bus Interface and External Bus.

26 IMP 2000

carr ies out self-check in two levels cal led software check and hardware check. Software check is carr ied out by a l l CPUs during power-up i n i t i a l i z a t i o n . I t comprises ROM, RAM, bus- in- terface and inputYoutput modules for each CPU. The CPU can control a check mode c i r c u i t on the BIF module. In the check mode I the external bus is disabled, and on the external side a short c i r c u i t is established from the output area on the BIF to the input area, and thus the CPU can control the proper funct ion of input /output buf- fers and opto- iso la tors . In the check mode 2 and 3 the output modules are contro l led for the a b i l i t y to receive the signals 0 and i and the input modules to give the signals 0 and I .

Hardware check is carr ied out cont inuously during the normal operation by the hardware c i r c u i t r y . A l l output modules have a supervision of board fa i lu res as well as disconnection and overload of the external connection. Two check status b i ts from each board indicate via the external bus to the CPU the current status of the board. The alarm handling rout ine test - these b i ts and takes necessary action whi le s igna l l i ng the f au l t to the operator.

7. CONSOLE SYSTEM

The console system is the inter face between the "machine in te l l i gence" and the human brains. I t must transform the character is t ics of the con- t ro l l ed process to a form that relates d i r ec t l y to the conceptions of the human operator. While the process inter face must re f l ec t only the character is t ics of the process, the console sys- tem must re f l ec t the "charac ter is t ics" of the operator as wel l . Therefore the IMP 2000 console system inc luding the f ron t plate lay-out may be custom-designed for each appl icat ion.

In the appl icat ion example given (Fig. 3) the f ron t plate contains the fo l lowing funct ions:

i . System mode push buttons for manual mode, one complete automatic cycle and f u l l y automatic mode.

2. Program select push buttons for optional funct ions that , when selected, w i l l be run along with the main cycle. These funct ions may be pre- programmed or they may be created by the user.

3. Parameter display and update f i e l d . I t com- prises push buttons for select ing process param- eters to be displayed on the alpha-numeric d is- play, which holds up to s ix parameters a l l at once. Below the display s ix push buttons are ar- ranged for select ing a parameter to be updated via the keyboard. A new value keyed in is ad- justed to the ind iv idual parameter speci f ica- t ions and tested for l i m i t v io la t ions before the actual updating takes place. Updating can take place any time during the automatic cycle but the new value w i l l not be used before the current machine funct ion is completed. In the actual example there are about 130 parameters (e.g. , set-points for pos i t ions, ve loc i t i es , pressures, t imers, counters, and temperatures) which may be fast and eas i ly surveyed and changed by the user.

While he concentrates on the e f fec t on the pro- cess the console system assures that the input values are compatible wi th the control system.

4. Slots for interchangeable "set-point memory" and "user program memory". These are bus-com- pat ib le peripheral devices with a so l id -s ta te , non-vo la t i le memory (EAPROM) mounted in a small r i g id box. When plugged into the s lo t one can store a l l user-defined parameters and user- created program sections, take them out and put them away together whith the tools for the spe- c i f i c product. When the same or a s l i g h t l y d i f - ferent product l i ne shall be establ ished, the plug in memory uni ts provide for a very fast and re l iab le set-up to the or ig ina l well tested con- d i t ions .

5. Alarm f i e l d with opt ical ind icat ion of major alarm condi t ions. In addi t ion a l l a larmcondi- t ions are recorded in memory, and they w i l l be displayed in the data display ( in groups of 6) when the alarm push button is pressed.

Together with actual alarms a l l wai t ing points in the automatic cycle are recorded cur rent ly at the time, where they become expected by the pro- gram and cancelled again when the wai t ing condi- t ion is f u l f i l l e d . The cur ren t ly recorded wait ing points w i l l be displayed when the "display cycle fa i l u res " push button is pressed. This gives a very select ive means of spott ing fau l t s , i f a contro l led sequence stops due toe e.g. a mis- funct ion ing l i m i t switch.

6. Optical ind icat ions (LED) for on/o f f l i m i t switches and valve outputs to give a d i rec t re- cord of the current state of the process.

7. A 20-character p r in te r to give production re- cords in a permanent wr i t ten form. This of fers a p o s s i b i l i t y to create productions s t a t i s t i c s in a way un-known from the conventional control

6 3 5

g o

e l g O O O e l e l

g o o o

g O

o o o o

,11"" • " ! ::::1

0 o : o o o o

' 0 0 ...-]

1 2 4

Fig. 3. IMP 2000 Console; 1. System Mode Selec- t i on ; 2. Program Select ion; 3. Parameter Control F ie ld; 4. Set Point and Program Memory; 5. Alarm Fie ld ; 6. Indicat ions for Limit Switches and Valves; 7. Pr in ter .

K. Clausen 27

systems. The recording capabil i ty can be extended to almost any degree by supplying a communica- tion l ink to a central computer plant.

8. Interactive communication. Especially during the power-up procedure the IMP 2000 with instruc- tions f u l l y spelled out prompts the operator, in his own language to respond appropriately. This releases him from the t r i v i a l thinking of oper- ating procedures so that he can concentrate on his real j o b - to make the process running.

8. SOFTWARE

The IMP 2000 is intended to perform a real- t ime control of indust r ia l processes. So, i t must be able to execute several control tasks simulta- neously. The ent i re process is s p l i t up into a set of possibly para l le l running functions, and each functions is assigned i t s own program sec- t ion. All these program sections are organized as co-routines under the control of a real- t ime monitor.

In this system the response time for the proces- sor is d i rec t l y related to the turn-around time for the current ly act ive co-routines. In time c r i t i c a l appl icat ions such as machine control where response times of a few mil l iseconds may be actual , the programmer must take special precau- t ions to prevent the act ive queue to grow too long in the c r i t i c a l phases. Neither should he introduce heavy mathematical manipulations that can hook up the processor for several m i l l i sec - onds without a release.

8.1. Injection Moulding Machine Control The 'IMP 2000 previously referred to Controls an injection moulding machine for plastic items. The machine consists of a mould unit and an injec- tion unit. The mould cavity is established by moving two mould plates together and pressing them t ight ly . The necessary hold-on force can be two or three hundred tons which indicates that the mould plates must be quite heavy machine parts. To minimize wear on the machine while ob- taining precise positioning of the mould plate i t must be moved with a well controlled accele- ration and deceleration.

The actual processing of the plastic material takes place in the injection unit. A screw in a cylinder is turned around, and while moving backward, the screw takes in plastic granulate. The material is melted by heating and compressed by the screw. The rate of heating, the p last ic i - zing speed and the compression must be controlled to obtain the r ight consistency. By applying a hydraulic pressure on the back of the screw the plastic melt is injected in the mould cavity. The speed of the injection must be controlled in ac- cordance with the cross-section of the cavity. When the cavity is f i l l e d , the pressure on the melt must decrease in a well defined rate while the melt is cooling down.

In summary the software system for an injection moulding machine must provide:

- a sequence control ler capable of controll ing parallel running sequences;

- a prof i le control ler to control analog outputs (flow and pressure valves) according to time as well as position dependent profi les. This section includes a great deal of mathematical computations;

- a temperature control ler; - a system supervisor and an alarm handling sec-

t ion; - an interactive console operation capable of

handling a great amount of machine parameters.

In the actual example the software system amounts to almost 22k of ROM, equally divided between the two CPUs. The console control ler and the prof i le control ler, both of which performs a lot of computation, are situated in one CPU, and the actual machine control is performed by the other CPU.

C O N C L U S I O N

With the technology level within the p last ic . moulding of to-day the actual machine control was performed perfectly well by the conven- tional control units of the "old days". What is gained by introducing the microprocessor, in addition to the hardware considerations given in section 1, is primarily:

- a much more detailed supervision scheme and an in te l l igent reaction on alarm condi- tions,

- a much more powerful console system with en- hanced capabil i ty of handling machine param- eters and fast and easy set-up procedures,

- a much more detailed production record in permanently written form.

But future research is l i ke ly to establish more complex control l ing strategies based on empirical expressions and adaptive regulators. This w i l l ult imately call for computing capa- b i l i t y and here the microprocessor-based con- t ro l system is superior to any other control system technology known to-day,

Ketil Clausen received his M. Sc. degree in Elec- trical Engineering from the Technical University of Denmark in 1971, specializing in digital dataco~nunication, computer science and digital electronics. Since 1974 he has been with BUHL AUTOMATIC, developing hardware and software for industrial control equipment.