Use of Microprocessors in Introductory Control laboratory

Control System Experiment: Use of Microprocessors in Introductory Control laboratory* R. La1 Tummala Department of Electrical Engineering and Systems Science, Michigan State University, East Lansing, MI 48824 ABSTRACT: Microprocessors have been extensively used in the design of real time control systems. To familiarize the students with microprocessors, several experiments are introduced in our introductory control laboratory. The purpose of this paper is ro give a detailed description of rhese experiments.

Introduction Theavailability of lowcostmicroprocessors created a great dealof interest inthedesignofmicroprocessor-based controlsystems.Tofamiliarizethestudents with the microprocessor control, a set of new experiments are added to the introductory control laboratory at MichiganStateUniversity [ I ] . In theseexperiments, the microprocessor is used to acquireanalogdata by interfacingan analog to digitalconverter: to outputa digital data which if used in conjunction withadigitaltoanalogconverter, providestheanalogoutput;tocontrolthe position ofa D.C.Servomotor;andto control the speed of a stepper motor. The purpose of this paper is to give a detailed description of these experiments and the equipment used.

in theseexper-

1) MEK 6800D2 Evaluation Kit available from the Motorola Corporation shown in Fig. 1, 2) An experiment board shown in Fig. 2, and 3) A position servo system with data acquisition board shown in Fig. 3. MEK6800D2evaluationmodule built around a 6800 microprocessor is a twoboardsystem withahexkeyboardand display. It also contains simple a *Received April 14. 1982. Accepted by Associate Editor G . H . Hostetter.

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Experiments

Fig. 2. Experimentboard used for microprocessor interfacing experiments.

Equipment Theequipmentused iments consists of

Fig. I . Assembled MEK 6800D2 kit

Phillips Controls, Cheshire, Conn., part #K-82701); and driver a SAA1027 (North American Phillips Control Corporation),ananalogtodigitalconverter (part #AD571K, Analog Devices, Inc.), andadigital to analogconverter(part #NE50 18. SigneticsCorporation).The block diagram is shown in Fig. 4. The positionservosystemshown in Fig. 3 is a locally built system with off the shelf components and28V permanent magnetD.C.Servomotormanufactured by Electro-craftCorporation,Hopkins, Minn. [2]. Thesystemwasdesigned in sucha waythatstudentscanperform bothanaloganddigitalcontrolexperiments.Theblockdiagram is shownin Fig. 5.

monitoring system called JBUG, random accessmemory (RAM) andparallelinput/output.TheJBUGmonitor lets the userentermachinelanguageprograms, debugthemandexecutethem.The kit also contains a serial interface which can beusedinconjunctionwithacassette tape recorder for storing programs. The parallel I/O chip,calledaPeripheral InterfaceAdapter(PIA),actuallycontainstwo 8 bit I/O portsfortheuser’s interface. When assembled, the kit providesafullyfunctionalmicrocomputer system and performs an adequate job in the microprocessor control experiments. Theexperimentboardconsistsofa 12Vsteppermontor(NorthAmerican

The students begin these experiments MEK by gainingfamiliaritywiththe 6800D2using thedocumentationprovidedwiththesystem by the manufacturer. They learn the step-by-step procedure to enter machine language programs, debug and execute them using the JBUG monitor [3]. Experimentsdealing withthemicroprocessor interfacing are performed next. In thispart,thestudentsinterfacethe microcomputertotheexternaldevices usingtheperipheralinterfaceadapter (PIA) chip. The PIA, which is housed in a 40 pin package, has two separate eight bidirectional data busses usually known as Port A and Port B for interfacingto the outside world. The 16 bidirectional input/output lines may be programmed to act either as imput or output lines. The datadirectionregister is used for this purpose(seeFig. 6) [4]. Thefollowing experiments are performed by interfacing thevariouscomponentsontheexperiment board and the microprocessor (Fig. 7). a) Initialization of PIA This is animportantpartofallthe experimentswherethe 16 bidirectional

control systems magazine

Fig. 3. PositionServosystem:

lines of PIA are defined as inputs and/or outputs. For example, the program shown in Fig. 8 defines all 8 data lines of “PORT A” as inputs and the 8 data lines of “PORT B” as outputs. b) Display different bit patterm on LED array Usingtheinitializationprocedurein part (a), the 8 data lines, PBO-PB7, that are connected to the LED’s through the buffer on the experiment board (Fig! 4) are set up as output lines. The desired bit patternsareoutputtedusingtheperipheral data register in the PIA. A sample program is shownin Fig. 9. This program outputs0,1,2,. . ., etc.intheconseca utiveorderon PBO-PB7 lineswith delay of specified duration.

( I ) Microcomputer, (2) Controller, ( 3 ) Motorandgears,and

(4) Power supply.

is determined by the following rpm (0) relations: Frequency =

#steps

w

rev

60

-* - Hz

(1)

Since the stepper motor we have chosen has 48 steps per revolution [ 5 ] , we get:

The program is given in Fig. 10. d) Data acquisition This experiment teaches the students to interface A/D andD/Aconverters, an important part of the microprocessor controlsystem.Thestudentswritea

Fig. 4. Block diagram of the experiment board shown in Fig. 2.

c) Speed control of stepper motor In this part, the speed control of stepper motoron the experiment board is controlled by outputtingavariablefrequency square wave. The microcomputer is thus used as variable a frequency square wave generator. Even though one of the PIA data lines can be used for this purpose, it is decided to use one of the control lines such as CB2 (Fig.6 ) in bit 3 followingmode.Thedesiredfrequency of the square wave for a given speed in

Fig. 5 . Block diagram of the position Servo system shown

in Fig. 3 .

8 DATA LINES FROM PERIPHFR~L

program to read an analog voltage using an A/D converter into microprocessor at adesiredsamplingrateandoutputthis value to a D/A converter.The COMeCtions are shown in Fig. 11. In this program, "PORT A" is set up as an 8 bit input port, and "PORT B" is used as an 8 bitoutputport.Use ofinterrupts are introduced.The flow chart ofthisprogram and the listings are shown in Fig. 12 and Fig. 13. The input to the A/D converter is asinewaveofagiven frequency.Thesamplingfrequency,is vaned to observe the aliasing effects.

a

DATA LINES FllOM PERlPHERIl

CONTROI LINES

K":;;"":"T",/"'"

I IVES

rj RSO = 0

fl RS1 = 0 CRA2 = 0

REGISTER A

CONTROL

i

REGISFER E

"0'

"1

'

INPUT

:

OUTPUT

- GRD - PWR l+5!

~

R

REGISTER A

]

INTERRUPT RESET READ A TO hlPU

I

H

S

RSl = 0 I )7

" \/

OR WRITE R E G 8 l SDTA t HT A SELECT FROM LINES TO PAPU MPU

REGISTER B F;

I

R

ENABLE

S

/ - "% -

hlPU FROM ADDRESS LINES

O

RS1 = 1 = 1

INTERRUPT L-"-f E TO hlPU CHIP SELECT FROM hlPU ADDRESS LINES

Fig. 6 . Internal architecture of Peripheral Interface Adapter (PIA). [4]

Experiment using Position Servo system

In this experiment, the microcomputer is introduced in the control loop of the position servo system as shownin Fig. 5. The voltage of the output potentiometer whichrepresentstheoutputposition is an inputted to the microcomputer through analogdigitalconverter(Fig. 14). The desiredpositionisenteredviathekeyboardasadigitalvalue.Themicrocomputer computes the error between the output position and the desired position. Thiserror is thenused to generatea control signal which is converted into an analog form withadigitaltoanalog converter and applied to the inputs of the 15). amplifiersdrivingthemotor(Fig. Thecontrolsignalgeneratedcan bea

Fig. 7. Experimental board andthe microprocessor.

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control systems magazine

Memory Loc (HEX)Instruction (HEX)

Comments Losd ACCA with zero

0000

86

0002

B7 8005

Enable Data Direction Register A

0005

B7 8007

Enable Direction Data Register B

00

B7 8004

0008

PAO-PA7 lines are inputs

FF

OOOB

86

OOOD

B7 8006

PBO-PB7 lines are, outputs

Memory Loc (HEX) Instruction (HEX) 0000

86

0002

B7 8007

0005

86

0007

B7 8006

Enable DDRB

OOOA Fig. 8. PIA Initialization.

Memory Loc (HEX)Instruction (HEX) 0000

86

0002

B7 8007

0005

86

0007

B7 8007

OOOA

CE HHHH

OOOD

09

OOOE 00 10

.

30

26

Comments

30

FF

Define PBO-PB7 as outputs

04 86

oooc

B7 8007

OOOF

86

0011

B7 8006

0014

CE

0017

09

0018

26

OOlA

4c

00 1B

20

Enable Peripheral data register B

01

Output "1" on the PBO-PB7

CB2 = 0

34

CB2 = 1

T

~

Delay = 2

FD

86

0011

B7 8007

CB2 = 0

0015

CE HHHH

T Delay = 3

0018

09

0019

26

OOlB

7E 0005

Comments

00

HHHH* Delay FD Increment ACCA Branch t o 0011

F4

*H = Hex number Delay = 1 3 Sec. ~ multiplied by the decimal value equivalent of the hex number, HHHH Fig. 9. LED program.

FD Jump to 0005

Fig. 10. Stepper motor control program.

DAC

ANALOG VOLTAGE OUTPUT

JI GND Fig. 11. Interfacing ADC and DAC to the microprocessor.

Memory locations 0000-000F contain the program t o set up PAO-PA7 lines as inputs and PBO-PB7 as outputs (see Figures).

21PFJ0-PB7 as WIPUIS 31CA2 line as Output 41Clea1 ntermpls

B? 86

neby a

sarnpk lime

Fig. 12. Flow chart for data acquisition using ADC and DAC.

2E

Memory Loc (HEX)

Instruction (HEX)

0010

86 04

0012

B7 8005

Enable peripheral - data Register A

0015

87 8007

Enable peripheral data Register B

0018

B6 8004

Clear Interrupts

OOlB

86 34

OOlD

8005

0020

3C

0022

B'7 8005

0025 34

86

0027

B7 8005

002A

B6 8005

002D

1

Comments

Output a convert pulse on the CA2 line

Conversion complete?

FB

002F

B6 8004

Read the output of AID and clear i n t e r rupts

0032

B7 8006

Output the value on PBO-PB7

0035

CE .HHHH

0038

09

0039

26 FD

003B

7E OOlB

Delay

Jump to 00 1B

_____

Fig. 13. Data acquisition program.

simple multiple of the error or the result of complex a controlalgorithmprogrammed microprocessor. into the Studentswriteprogramstocontrolthe position and study the effects of sampling period on the system response. An example is shown in Fig. 15 and Fig. 16. Advanced students program complex such as PID and control algorithms digital equivalents of a n a l o g compensating networks and determine the effects of these on the system response.

Concluding Remarks

I Fig. 14. Data acquisition board associated withthe position Servo.

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The experiments described in this papercomplement verywellwiththe other experiments in the lab dealing with the analog control systems [I], and form a basis to understand and design real time control systems using a microcomputer. We found that this can be done witha

control systems magazine

ZIPBb-PB7 as outputs 3)Clearinterrupts

(HEX) Instruction Memory Loc (HEX) Comments

-V Outputaconvertpulseona

Memory locations 0000-0031 contain the same program as g i v e n i n F i g u r e 14 Desired position is stored in location 0080. Actual position is stored in l o c a t i o n 0081.

CA2 line

97

0032

Store a c t ut ahle

81

position 96

0036

C90o m p4u1t e

0038

B7

003A

C EH H H H

003DDelay

09

J

003E

26

on P B W B 7 lines

0040

7 E OOlB

&+ Determine the error between the desired position and the actual position

Output the error

80

0034

Loop

8006

the e r r o r Otuhtep u t

error

FD Repeat

Delay (sample time)

Fig. 16. Program

Fig. 15. Flow chart for position control

-

minimal comouter background. Many of the students are motivatedbythis experience and pursue further work in the form of independent study. This usually and construction of involves the design microprocessor based systems. Typical Phillips Controls, Cheshire, student projects in the past included the microprocessor controlled growth chamb e r a n d 3 DOF mechanical manipulator. ~~~

[3] MEK 6800D2 Evaluation Manual.

Motorola Corporation. [4] R. Bishop,“Basicmicroprocessorsand the 6800,” Hayden Book Company, 1979. [SI Data sheets from North American CT.

References R . L. Tummala,1980.“Control Systems Lab Manual.” Departnent of Electrical Engineering and Systems Service, Michigan State University, East Lansing, MI. [2] D . C . Motors, Speed Controls, ServoSystems, AnEngineeringHandbook by Electro-craft Corporation, Hopkins, 1978. MN. Technology. of Institute Madras ing from [I]

February 1983

R. La1 Tummala (S‘66-M‘70) was born in Pamarru. India, on May 22. 1944. He received the B.Sc. degree in mathematics, a pn hd y s i c s , chemistryfromAnd h rUa n i v e r s i t y . N’altair. India. the D.M.I.T.degree in electronicscngineer-

for position control. Madras,India,theM.Tech.degree in industrial electronics from the Indian Institute of Technology,Kharagpur,India,andthe Ph.D.degree in electricalengineering and systems science from Michigan State Unircrsity,EastLansing, in 1961,1964, 1966, and 1970. respectively.Since I966 hehasbeen with Michigan State University, where he has beenResearchAssistant,Human ILearning Research Institute (1966-1967). Kesearch Assistant, Department of Electrical Engineering (1967-1970), and Rcsearch Associate. EnvironmentalSystemsProgram, Division of Engineering Kesearch (1970-1972). He i5 prcsently an Associate Professor in the and Department of ElectricalEngineering Systems Science and the Department of tintomology.Hiscurrentresearchinterestsarc in digital control. robotics and \ystems modeling. He is the author of soera1 papers in theseareas.Dr.Tummala is aSenior Member of the Kobotics intcrnational o l the Society 01 1.Ianufacturiny tingincsrr.

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