A Review Paper on Microprocessor Based Controller Programming
ABSTRACT:
Designing of microprocessor based controllers requires specific
hardware as well as software programming. Programming depends upon type of the
software whether operating software or application software. Programming
requires knowledge of system configuration and controller specific programming.
Programs are always in digital form so microprocessor can control directly at
digital level called Direct Digital Control(DDC).
Keywords: Controller Software, DDC, Controller Configuration,
Controller Programming, Custom Level Programming,Digital Form
1. INTRODUCTION
In
the early 1960 computer based controllers were used. They were having one main
frame computer and all control action was dependent on it, moreover they were
costly. But with the advent of microprocessor cost of controlling the plant
decreased very less.
In actual a microprocessor is a computer on a
chip, and high-density memories reduced costs and package size dr amat i cal l
y and i ncreased appl i cat i on fl exi bi l i t y. These controllers’ measur e si gnal s from
sensors, per for m cont rol rout i nes i n software programs, and take
corrective action in the form of output signals to
actuators.
Since the programs are in digital form, the controllers perform what is known
as direct digital control (DDC). Microprocessor can directly control the plant
digitally. A direct digital control can be defined as the controller which
updates the process as function of measured output variable and input provided.
As the output world talks in analog form so for control digitally it has to be
converted into digital form. For this A/D and D/A converters are used as shown
in fig. 1
Figure1: A microprocessor based control system use A/D- D/A converter
A
block diagram of microprocessor based digital
control system along is shown in
figure2 [1].
Figure2: Mi croprocessor based digital control
system
Figure
2 shows the analogi nput and output hrough A/D and D/A converter.
In
addition, a communications port is not only a desirable feature but a
requirement for program tuning or interfacing with a central computer or building
management system. Timing for
microprocessor operation is provided by a battery-backed clock. The
clock operates in the microsecond range controlling execution of program
instructions. Program memory holds the basic instruction set for controller
operation as well as for the application programs. Memory size and type vary
depending on the application and whether the controller is considered a
dedicated purpose or general purpose device. Dedicated purpose configurable
controllers normally have st andard programs and are fur ni shed wi t h read
onl y memory (ROM) or programmable read only memory (PROM.). General purpose
controllers often accommodate a variety of
individual customprograms
and are
supplied with field - alterable
memories such as electrically erasable, programmable, read only memory (EEPROM)
or flash memory. Memories used to hold the program for a controller must be
nonvolatile, that is, they retain the program data during power outages. A/D
converters for DDC applications normally range from8 to 12 bits depending on
the application. An 8bit A/D converter provides a resolution of one count in
256. A 12-bit A/D converter provides a resolution of one count in 4096. If the A/D
converter is set up to provide a binary coded decimal (BCD)output, a 12-bit converter
can provide values from 0 to 999,0 to99.9, or 0 to 9.99 depending on the decimal
placement [3].
3. CONTROLLER SOFTWARE
Although
use of microprocessor controller for any application depends upon the hardware
but software
determines
the functionality. Controller software falls basically into two categories:
1. Operating software which controls the basic
operation of the controller
2. Application software which addresses the
unique control requirements of specific
applications
3.1 Operating software
It
is generally stored in volatile memory such as ROM, PROM. Operating software
includes the operating system (OS) and routines for task scheduling, I/O
scanning; priority interrupt processing, A/D and D/A conversion, and access and
display of control program variables such as set points, temperature values,
parameters , and data
file information .
Tasks
are scheduled sequentially and
interlaced with I/O scanning and other routine tasks in such a way as to make operation
appear almost simultaneous[4]. If any higher priority task appears to operating
software then current going task is ceased and data held in registers and
accumulators are temporarily transferred to temporary registers. These
interrupt requests are processed by priority interrupt register. When interrupt
task is over then normal routine is resumed and data is transferred back from
temporary registers to mainstream. The effect of these interrupts is
transparent to the application that the controller is controlling
3.2
Application Software
Application
software includes direct digital control, energy management, lighting control,
and event initiated programs plus other alarm and monitoring software typically
classified as building management functions. The system allows application
programs t o be used individually or in combinat ion. For example, the same hardware and operating
software can be used for a new or existing
building
control by using different programs to match the application. An
existing building, for example, might
require
energy management software to be added to the existing control system. A new
building, however, might require a combination
of direct digital control and energy management software[5].
3.2.1
DIRECT DIGITAL CONTROL SOFTWARE
DDC
software is used for specific control actions. These are set of standard DDC
operators. Key elements in most direct digital control programs are the PID and
the enhanced EPID and ANPID algorithms. While the P, PI, PID, EPID, and ANPID
operators provide the basic control action, there are many other operators that
enhance and extend the control program. Some other typical operators are shown
in Table 1. These operators are computer statements that denote specific DDC
operations to be performed in the controller [6]. Math, time/calendar, and other
calculation routines (such as calculating an enthalpy value from inputs of
temperature and humidity) are also required
4. CONTROLLER PROGRAMMING
Controller
programming makes the controller usable for a specific control action. Programming of microcomputer-based
controllers can be subdivided into four discrete categories:
1. Configuration programming
2. System initialization programming
3
. Data file programming
4. Custom control programming
Some
controllers require all four levels of program entry while other controllers,
used for standardized applications, require fewer levels.
Configuration
programming matches the which hardware and software matches the control action
required. It requires the selection of both hardware and software package to
match the application requirement.
System
initialization programming consists of entering appropriate start up values
using a keypad or a
keyboard. Start up data parameters include set point ,
throttling range, gain, reset
time, time of day,
occupancy
time, and night set back temperature
[7].
These data are equivalent to the settings on amechanical control
system, but there are usually
more items because of t he added functionality of the digital control
system. Requirement of data file
programming depends upon whether the system variables are fixed or variable.
For example at zonal level
programming where input sensors
are fixed and programmer knows whichrelay will get output then the use of data file programming isirrel
evant . But at the system level programming where controller
controls wide variety of sensors and gives out put to various relays, use of data file
programming is must . For the
controller to properly process
input data, for example,
it must know if the point type is
analog or digital . If the point is analog,
the controller must know the
sensor type, the range, whether or not the input
value is linear, whet her or
not alarm limits are assigned, what the high and low alarm limit values are if limits are assigned, and if there is a lockout point .
See Table2. If the point is
digital, the controller must know its
normal state (open or closed) [8],
whether the given state is an alarm state
or merely a status condition, and whether or not the conditiont riggers an event initiated
program.
Custom
control programming is the most involved programming category. Custom control programming
requires
a step-by-step procedure that closely
resembles standard computer programming.
A macroview
of
the basic tasks is shown in Figure 4.
5. CONCLUSION
Microprocessor
based controllers although depends upon the hardware of controller but the main
behavioris
defined in software programming.
Application software is used if a specific cont rolling
action
is needed. Before programming the
controller values initial parameters is
considered. Complexity
of
programming also depends upon the number of controllers to be controlled, input
is analog or digital .
If
many inputs are coming to controller then a data file has to be maintained so
that just by lookinginto
that file constraints of programming can be
identified.
tanks for reading...
REFERENCES
[1] S.D. Kraft and Edward T. Wall,‖ Experimental
Microprocessor-Based Adaptive Control System‖ IEE Control Systems Magazine
[2] www.itswtech.org/Lec/dr.basim/3/lec1.pdf
[3]
http://www.ddc-online.org/Digital-Control-Systems/Introduction-to-Direct-Digital-Control-Systems.html
[4] Robert Yung, Stefan Rusu,
Ken Shoemaker,‖ Future Trend of Microprocessor Design‖ ESSCIRC 2002
[5] Katz, P.: 1981, ―Digital Control System‖,
Springer-Verlag, Berlin
[6]
Alfred C. Weaver, ―A real-time, multi-task programming language for
microprocessor-based industrial process control‖, ACM '78 Proceedings of
the 1978 annual conference - Volume 2 Pages 522 – 525
[7]
Chang-Jiu Chen, Wei-Min Cheng, Hung-Yue Tsai and Jen- Cheieh Wu,‖ A
Quasi-Delay-Insensitive Microprocessor Core Implementation for Microcontrollers‖,
Journal Of Information Science And Engineering 25, 543-557 (2009)
[8]
J.H. Lee, W. C. Lee, and K. R. Cho, ―A novel asynchronous pipeline architecture
for CISC type embedded
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