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Week-3
3-7 Jan 2014
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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
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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
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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
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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
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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
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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
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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??????
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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
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Boolean Representation - Example
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Example
Make Boolean Function & Simplify!!!
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Example
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Exercise
Convert to Boolean Logic Simplify and then write the ladder logic
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Karnaugh Maps
Given a Truth table it can be used to get a (Simple) Boolean Function
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Karnaugh Maps Example
Asher JohnSticky Note. when we have to combine two blocks from columns and rows. rows first and then columns
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Rslogix 500
Mainly used for Micro Logix, Flex logix & SLCs
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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)
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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:
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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
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Example
These scan times are just an example to clarify things and dont depict the actual scan times of a PLC
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An Actual Timing Diagram
Real timing diagram for the Scenario mentioned before
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Another Example
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Draw the Timing Diagram
Draw the Timing diagram of corresponding outputs to the Inputs
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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
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Siemens
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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
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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
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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
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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
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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
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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
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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.
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Addressing Special Bits
RsLogix 500 RsLogix 5000
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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
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Example of Off Delay Timer
The preset value is 3500ms, so delay of 3.5 seconds.
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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?
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Example
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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
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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
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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
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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
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Solve
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Solve
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Timing Diagram of a Retentive Timer (Assignment 3)
Draw the timing diagram of the following retentive timer
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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
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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)
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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)
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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)
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Example of Count Up Counter
Contact B is used to Reset the counter
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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
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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)
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Example of Counters
Count Up & Count Down Counters can have the same registers
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Cascading Counters
What is happening here?
When will the last counter done bit (DN) be set?
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What is the output?
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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
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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
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Solve
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