Week-3

3-7 Jan 2014

Objectives Memory & File Organization and Addressing

Examples of Boolean and Karnaugh Maps to Ladder Logic

Operation of Latches

Operation of Timers Rockwell Automation

MODICON

GE Fanuc

Operation of Counters Rockwell Automation

MODICON

GE Fanuc

Rockwell Memory & File Organization

Understanding File Organization and Addressing is very essential to program a PLC

There exists two types of memories in Rockwell PLCs (RAM)

Program Memory

Data Memory

Each contains 256 files (0-255)

Program Memory:

File 0 contains processor type, I/O Configurations etc

File 1 is reserved

File 2 contains the main ladder logic

File 3-255 are user created according to subroutines in the main ladder

Data Memory:

Data Memory also has 256 files

Mainly contains the status of I/O and other instructions used in the main ladder and subroutine ladders

There exists different files with different functions:

File 0 (O) : Stores the status of outputs. If you want to change the status of the output you could put 0 or 1 in the correct bit

File 1 (I) : Stores the status of the inputs. You can check the status of any input by looking in the file

File 2 (S): Mainly stores status bits corresponding to the processors state.

File 3 (B): Used to store bit information. You can store different information relating to contacts and coils.

File 4 (T): Used to store Timer information.

File 5 (C): Used to store data corresponding to Counters

File 6 (R): Used for control, example when working with Sequencers & Shift registers

Rockwell Memory & File Organization

File 7 (N): Used to store Integers or Bit information

File 8 (F): Used to store floating point numbers. These numbers could be gains for PID blocks or outputs corresponding to them.

File 9-255: These files are user defined. The user can define them according to his requirements. They can be used to store integers, floating points etc

Rockwell Memory & File Organization

Memory Addressing

Memory addressing is the processing of reading or writing data to the files

The first letter in the input address is called the identifier

The second letter is the file number (the default number is 1)

The next item is the delimiter (colon)

The next item after limiter is the slot number (in the chassis) and after that the Bit number

I1:0/1 Input Register (File 1)

Slot 0

Channel 1

Memory Addressing

File Type Identifier File Number

Output O 0

Input I 1

Status S 2

Bit B 3

Timer T 4

Counter C 5

Control R 6

Integer N 7

Float F 8

Memory Addressing

Power

Supply

CPU

Input

Output

Input

Output

Output

SLOT NO. 0 1 2 3 4 5

How would you address different slots and channels within those

slots??????

Similarly Timer and Counter Files can also be addressed however they contain additional parameters that can be addressed

Timers & Counters and additional parameters that can be addressed in them will be discussed in upcoming lectures

Memory Addressing

Boolean Representation - Example

Example

Make Boolean Function & Simplify!!!

Example

Exercise

Convert to Boolean Logic Simplify and then write the ladder logic

Karnaugh Maps

Given a Truth table it can be used to get a (Simple) Boolean Function

Karnaugh Maps Example

Asher JohnSticky Note. when we have to combine two blocks from columns and rows. rows first and then columns

Rslogix 500

Mainly used for Micro Logix, Flex logix & SLCs

Timers & Counters - Motivation

Complex systems cannot be controlled by Combinatorial Logic alone

A system can be Event driven, Time driven or a combination of both

Basic events which need to catered for are (Event + Time based):

Delays

Count of Events

Latch Or Unlatch (to turn something On or Off)

Common theme in all these events are:

How long? (Time based)

How many? (Count of events)

Response of a Device in Event Driven Systems

The response of a device to an event can be classified into following two categories:

Logical Response

Event Response

Consider the scenario when a push button is pressed, the device responds in the following manner:

Latches

Latch & Unlatch:

It can be considered as a sticky switch when it is turned on it remains ON

It must be pulled (unlatched) to turn it off

Different instructions are used to Latch & Unlatch the variables

Example

These scan times are just an example to clarify things and dont depict the actual scan times of a PLC

An Actual Timing Diagram

Real timing diagram for the Scenario mentioned before

Another Example

Draw the Timing Diagram

Draw the Timing diagram of corresponding outputs to the Inputs

Latches in case of Other Vendors

Latch & Unlatch blocks are not used universally by all PLC vendors

Siemens uses SR Flip flops to perform latching & unlatching operations

SR Flip Flop:

S R Action

0 0 No Change

1 0 Q=1

0 1 Q=0

1 1 Not Specified

Siemens

Timers

Mainly used for providing delays in between sequences & operations

There are 4 different types of Timers:

Off Delay Timers

On Delay Timers

Retentive On timers

Retentive Off timers

Examples of Usage:

Consider a garage light which should remain ON for 2 minutes before turning off.

Non Retentive

Off Delay Timers

The timer turns ON as soon as the input turns high

Starts incrementing when the input has turned false and turns OFF when a certain time has been achieved

Examples:

A garage light which should remain ON for 2 minutes before turning off.

Consider a car whose ignition key has been turned off but the car engine remain ON for some time

Cooling fans remain ON for some time after the oven has been turned off

ON Delay Timers

Starts incrementing when the input has becomes true and turns ON when a certain time has been achieved

It turns OFF immediately as the input turns OFF.

Examples:

Consider a car whose ignition key has been turned ON but the car engine turns ON after some delay

An On delay timer would allow an oven to reach a specific temperature before starting production

Retentive Timers

Retentive timers:

They dont lose their accumulated values once the enable input lines go low

They retain the accumulated value until the enable input lines goes high again

They function like stop watches. They can start and stop and retain their current values until a reset button is pressed

Non Retentive timers:

The timer value goes to Zero once the enable input goes low

Thus non retentive timers lose the accumulated value

Basic Similarities in Timers

There are some basic common aspects in a Timer blocks made by different PLC vendors:

Timers will have a number to identify them (for example T7 in case of Rockwell)

Time Base:

Timers can be programmed with different time basis, for example 1 second, 0.1 second and 0.01 second

Example:

If a timer has 0.1 second time base and the user entered 50 as the number of delay increments then delay would be 5 seconds

Preset Value:

The preset value is the number of increments the timer has to count before it changes it output. 50 is the preset value in the previous case

Accumulated Value:

It refers to the current increment the timer has reached during its operation

Rockwell Timers

On Delay Timer: It starts accumulating when the rung

becomes true and continues until the

preset value becomes equal to the accumulated value or the rung goes false

Basic Symbol used is T and the file number is 4 (T4).

Status Bits Usage: Enable Bit (EN): It turns on immediately when the rung goes true and

remains set until the rung goes false or timer is reset

Timing Bit (TT): It remains true when the rung goes true or accumulated value is less then preset value

Done Bit (DN): It is set when the accumulated value equals the preset value

Example of On Delay Timer

The preset value is 4000ms, so delay of 4 seconds. The preset value is 4000ms, so delay of 4 seconds.

Asher JohnSticky Noteas TT goes down DN bit gets ON.

Addressing Special Bits

RsLogix 500 RsLogix 5000

Rockwell Timers

Off Delay Timer: It starts accumulating when the rung

becomes False and continues until the

preset value becomes equal to the accumulated value or the rung goes True

Status Bits Usage: Enable Bit (EN): It turns on immediately when the rung goes true and

remains set until the rung goes false or timer is reset

Timing Bit (TT): It remains true when the rung goes False and accumulated value is less then preset value

Done Bit (DN): It is set when rung becomes true and reset when accumulated value is equal to preset value

Example of Off Delay Timer

The preset value is 3500ms, so delay of 3.5 seconds.

Retentive ON timer

Similar to ON timer except that it retains its value.

The preset value is 4000ms, so delay of 4 seconds

How can we use the timer after the cycle has completed?

Example

Example

Consider the scenario in which a start button turns on the Heater

and the Stop button (normally closed) turns it off. Initially there is a

delay of 10 sec before the heater turns ON. After the heater is turned OFF the cooling fans remain ON for 5 minutes

Cascaded Timers

The timers are connected to each other and thus are called

cascaded timers

Each timer drives the other timer

Mainly used when a single timer cant provide the delay required

Timers of other PLC Vendors

GE FANUC TIMERS & CONTACTS:

There are of the following basic types:

ONDTR (On delay timer) Retentive timer

OFDT (Off delay timer) Retentive timer

TMR (On delay timer) Non retentive timer

Contact addressing in GE FANUC:

%I represents inputs %I0005 represents real input 5

%Q represents outputs %Q0003 represents real output 3

%R represents system registers

%AI Analog Inputs

%AQ Analog Outputs

ONDTR

TB

Time

Base R

PV

%R0001

Enable Input Output ONDTR

TB

R

PV

%R0001

Enable Input Output

Time

Base

ONDTR

TB

R

PV

%R0001

Enable Input Output ONDTR

TB

R

PV

%R0001

Enable Input ONDTR

TB

R

PV

%R0001

Enable Input ONDTR

TB

R

PV

%R0001

Enable Input Output

Time

Base

ONDTR

TB

R

PV

%R0001

Enable Input ONDTR

TB

R

PV

%R0001

Enable Input ONDTR

TB

R

PV

%R0001

Enable Input Output

Timers of other PLC Vendors Gould Modicon Timers & Contacts:

The figure shows a Non retentive Gould

Modicon Timer.

The delay can be calculated by multiplying the

preset value with the time base

The Timer has two outputs, one which operates when the timer accumulated value equals the preset value and the other output is

inverted

Contact Addressing:

0 at the start represents outputs 0005 represents the 5th real output

1 at the start represents inputs 1002 represents the 2nd real input

4 at the start represents Storage registers example 4004

Reset

Preset Value

Time Base

Storage Register

Enable Output

Output

Solve

Solve

Timing Diagram of a Retentive Timer (Assignment 3)

Draw the timing diagram of the following retentive timer

Counters

Counters are used in many important industrial applications

Mainly used in Production lines where the items have to be counted

When we are counting the number of products we might use a count up timer

When we are counting the number of parts left we might use a count down timer

The choice of counter to be used depends on the application

Operation of Counter

There are different types of counters:

Count up

Count down

They use a low to high transition for counting action

Timers count time increments whereas counters count pulses on input lines

Timer increments its value with each low to high transition and turns ON when the accumulated value equals the preset value

Counters are edge triggered devices and dont accumulate when the level is remain high (level triggered)

Rockwell Automation Counters

Rockwell Automation Counters Use the filer number 5 for counters and the symbol C

So counter values would be stored in C5:0

Counters are retentive and a reset bit must be used to return the accumulated value to zero

Counters have the following essential elements: CU (Count Up bit)

CD (Count Down bit)

DN (Done bit)

OV (Overflow bit)

UN (Underflow bit)

PRE (Preset value)

ACC (Accumulated value)

Count Up Timers

Count Up Timers (Retentive): The accumulator (ACC) value increases

with every low to high transition

The done bit (DN) is set when the accumulated value equals the preset value

The over flow bit (OV) turns on when the counter value increases by 32,767. It then wraps around and starts counting from -32,768 (this is how 16 bit signed numbers are stored)

The count up (CU) shows that the Counter has been enabled (it turns on when ever the rung condition goes true)

Example of Count Up Counter

Contact B is used to Reset the counter

Example

A count up (CU) Counter is used to remove the 6th Part of

every 11 parts that are detected and then resets the

counters

Count Down Counter

Count Down Timers (Retentive): The accumulator (ACC) value decreases

with every low to high transition

The done bit (DN) is set when the accumulated value equals or greater then the preset value

The over flow bit (OV) turns on when the counter value decreases by -32,768. It then wraps around and starts counting from 32,767

The count down (CD) shows that the Counter has been enabled (it turns on when ever the rung condition goes true)

Example of Counters

Count Up & Count Down Counters can have the same registers

Cascading Counters

What is happening here?

When will the last counter done bit (DN) be set?

What is the output?

Counters from Other Vendors

GE FANUC TIMERS:

There are of the following basic types:

UPCTR (Up counter) Retentive Counter

DNCTR (Down Counter) Retentive Counter

UPCTR:

Every time the input turns High it increments the Counter value by 1 and if it is equal to the preset value, the counter turn ON

The R input is used to reset the counter

DNCTR:

Every time the input turns High it decrements the Counter value by 1 and if it is equal to the preset value, the counter turn ON

The R input is used to reset the counter

ONDTR

TB

R

PV

%R0001

Enable Input ONDTR

TB

R

PV

%R0001

Enable Input UPCTR

R

PV

%R0001

Enable Input Output

Gould MODICON Counters:

When the input pin transitions from

Low to high the counter increments the

Counter value

The reset pin must be high for the counter to

Count

The output value goes high when the input value equals the preset value

The counter also provides an inverted output

Counters from Other Vendors

Reset

Preset Value

CTR

Storage Register

Enable Output

Output

Solve