Programmable logic devices are one of many electronic
devices that used to build and configure the

Digital circuit. Compare to logic gate, this is undefined
function at the time of manufacture. First

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

Programmable logic was introduced at the time of 1969. It
was founded by Motorola, known as XC-157.

This is composed of 12gates and 30 uncommitted input or
outputs. After that, Texas instruments

made another new programmable logic that programmable IC.
This is based on IBM-read associative

with Memory or ROM. This device is known as the TMS 2000.
This device is composed of 17 inputs and

18 outputs with 8 JK flip flop for memory. In 1971, Company
knows as General Electric founded new

programmable logic device. This electronic device improved
on IBM’s ROAM with allowing multilevel

logic. In 1973 National Semiconductor introduced a PLA
device with 14 inputs and 8 outputs with no

memory registers.

      There are various
advantages that programmable logic devices have. First, There is no need for
the

time-consuming logic design of random-logic gate. This makes
program quicker than just wiring

bunch of electronic circuit with complex system. Second,
checking the design is easy, and change the

design is also easy. Third, Layout is far simpler than that
for random-logic gate. So, it is less time-

consuming. Fourth, PLA is a very inexpensive approach,
greatly shortening designing time. PLAs have the

following disadvantages compared with random-logic gate
networks.

    There are several
disadvantages of the programmable logic devices. First, for storing the same

function or tasks, PLAs can be smaller than ROMs. Second, Design
and the layout of random-logic gate

networks are far more tedious and time- consuming.

      Also, there are
many different types of logic devices. First, I want to talk about SPLD. This
is simplest,

and smallest, and not much expensive form of programmable
logic device. This is very similar to a

Complex form, but an SPLD will have less IO pins and programmable
components, consumes less

Power and requires special programming device to figure out.
This is non-volatile and remaining their

state after power is removed.  Microchip SPLD products consist of industry
standard 16V8 and 22V10s in

a variety of voltage. They typically composed of 4 to 22
fully connected macro-cells. These macro-cells

typically composed of some combinatorial logic like And /OR
gate. It used in boards to change the

standard basic logic of And/OR gate.

       Another unique
type of programming logic devices are known as the CPLD. It stands for complex

programmable logic device. It is device that have the architectural
features of both, PALS and FPGAs.

CPLD is composed of two features. Non-volatile memory, and
legacy CPLD devices. CPLD is an

evolutionary step from even smaller devices than PLAs.

     The main
distinction between FPGA and CPLD device architectures is that FPGAs are internally
based

on look-up tables. FPGA is stands for the field-programmable
gate array. This is an integrated circuit

designed to be configured by a customer or a designer after
manufacturing – hence “field-

programmable”. This is composed of array of
programmable logic blocks. Logic blocks exist  to perform

complex combinational functions, simply logic gates like
AND/XOR. This device trying to implement

complex digital computations. Examples are PAL known as
programmable array logic, General array

logic, Programmable logic array, programmable logic
device.  Most important feature of SPLD
is

macro-cell. Macro-cell is fully connected to the others in
the device. Some of SPLDs use either fuses or

non-volatile memory cells such as EPROM, EEPROM, or FLASH to
define the functionality. Most SPLD’s

are used within EPROM, EEPROM, or FLASH to define the
functionality.

   CPLD is compose of
the two to 64 SPLDs. CPLD composed of tens to a few hundred macro-cells.

CPLD is just multiple PAL- logic blocks with 4 to 16
macro-cells.  Field Programmable Gate
Array are

 Logic Cell Array,
programmable ASIC, FLEX, APEX, ACT, ORCA, Vertex, Quick logic. Those are came
from

each different company. This is distinct from SPLD and
CPLD. 

    Actually Programmable
Logic Controller have features are sequential control, counters and timers,

ease of programming, reliable controlling capabilities.  PLC is using for washing machine, elevator,
traffic

signal. Programmable logic have multiple modules. Such as CPU
module, Power supply module, I/O

module, PLC Architecture. Each module have various different
characteristics.

    First, CPU module
is just central processor that performing computation, processing data by
accepting

input and  output.
Second, Power supply module is supply the power to the whole system by
converting

AC power to DC power for CPU and I/O module. I/O module is
input and output module of the PLC for

the connection 
between sensor and actuator. Sensors are such as measuring the temperature,
pressure

and flows. There are two type of I/O modules are digital and
analog. Another type is Communication

Interface Module. This transfers the information between a
CPU and communication network. Central

processing Unit of programmable logic controller consists of
operating system and user programs.

   There are some of
steps of the running for PLC Scan cycle. First, Operating system starts cycling
and

monitoring. The CPU starts to read the data from input
module and checks status of all inputs. The

CPU executing the application program written in
relay-ladder logic/ PLC programming language. Then,

CPU performs communication tasks.  And data goes through the output modules and
outputs are

automatically automated. Pressure switch, temperature switch
are input field devices. And manual push

buttons are hardwired to an input module.

  The glass industry
run by the Programmable logic devices. During the 1980s, Programmable logic

controls widely used to assembling of workshop of the glass
industry. While the increasing the demand

of Programmable logic, PLC became known as intelligent
device for the glass industry. Glass industry is

a type of the distributed control system attribute with
Programmable logic device.

   Programmable logic
control also used in Cement industry. DCS with bus technology is used in the

production of the cement industry. The PLC is in user mode
of SCADA. SCADA mode configuring the PLC

and main computer that control the programmable logic
control.  The main computer have 2
stations

which knowns as the Slave and master station.  The most common function of Programmable logic

device is actually industrial automation.

    Their programming language is sequence of
binary number of machine code. This is used to translate

mnemonics into the code of machine. Those devices using
specific symbols known as the ladder logic.

Ladder logic is the schematic of the relay circuit diagrams.
This is the diagram that composed of two

Vertical lines representing the power rails, horizontal
lines between two verticals are representation of

the relay ladder logic circuit.  

    Ladder logics have
their own unique features. First, Power flows from left to right. Second, Output
on

right side cannot be connected directly with left side. Third,
Contact cannot be placed on the right of

output. Fourth, Each rung contains one output at least.
Fifth, each output can be used only once in the

program. Sixth, a particular input a/o output can appear in
more than one rung of a ladder.

Seventh, the inputs a/o outputs are all identified by their
addresses, the notation used depending on the

PLC manufacturer.

    Most fundamental
symbols of the programmable logic is instructions. There are many kinds of the

Symbol like Examine if closed, which is normally open. Examine
if closed, which is normally closed.

OTE, which is Output Enable. The instruction is the action of
the conventional relay coil. TON, which is

stands for the timer ON. If enabled until set-point is
reached then the timer output goes true, and stays

true until the input (enable) line goes false. Off Timer,
which is stands for TOF. OFF timers begin timing

on a true-to-false transition, and continue timing as long
as the preceding logic remains false. When the

time equals the set-point the Time-OFF, output goes on, and
stays on until the rung goes true.  RTO

stands for the retentive timer ON. This does not reset the time
when the input condition goes false.

There are two types of the latching relays. Output latch and
Output Unlatch are stands for OTL, and

OTU. If the unlatch instruction is true then the relay
output is false. Latch and unlatch relays are

separate operators. JSR is Jump to subroutine. This is for
the umping from one rung.

    There is also
international standard of the logic controller. This is known as the IEC 61131.
This is

first independent standardized programming language for
industrial automation. Demand is driven by

the increasing software complexity of control and automation
requirements. Labor cost, and

cost of control software has a major cause of the developing
of the international Programmable logic

control.  This device combined
with revolutionary architectures to be able to control an entire controller

to be delivered in an embedded system.

     This enables to transport
automation with the solutions to other platforms improved over PLC

Applications. IEC have unique elements. Such as Data Typing,
Configuration, Resources, and Tasks,

Program Organizations Units, unique type of programing
languages, and Co-De-Sys.

     This is one of
the example of the code of the IEC.

 FOR I:=1 TO 16 BY 1
DO

ARRAY_OUTPUTSI := FALSE;

END_FOR;

 

   IEC encouraged
function block reuse in 1993. It is important to consider robustness of the
software.

This is easier to transfers, no Steep Curve, no benefit from
function block. 

Author