Tag Archives: indirect addressing plc

Building a PLC Program Part 4 – Traffic Light

In part 1 we looked at writing PLC programs to control a traffic light using discrete bits and then using timed sequencing using indirect addressing. Part 2 used indirect addressing for inputs as well as output to control the sequence of pneumatic (air) cylinders in the program. Part 3 returned to the traffic light application and expand our program significantly. We looked at the sequence of operations using Input, output, and mask tables. Part 4 will now continue with the programming of the logic in the PLC.


Let’s look at the sequence that we are controlling – Building a PLC Program – Traffic Light

Note that I have color-coded the outputs that will be on in the sequence. This makes it easier to read how the lights will behave. All bits without ‘1’ are assumed to be ‘0’. The pedestrian walk signals flash before they change to walk signals.

The weekend sequence looks like this. We have an overlap of the red signal lights. The arrows are not used.
Building a PLC Program Part 4 - Traffic Light

The weekday off-peak times sequence looks like this. We have an advanced flashing green light for the north and west traffic.
Building a PLC Program Part 4 - Traffic Light

The weekday peak times sequence is as follows. The turn arrows have been added for the north/south and west/east directions.
Building a PLC Program Part 4 - Traffic Light

It is important to note that the sequencing and information contained in these charts must be understood fully before programming can begin. Take the time to review and understand the following tables. Here is a copy of the excel table complete with the inputs, mask, and outputs.

Advantages of Sequencers – Building a PLC Program  – Traffic Light

This method of programming can have a vast number of applications. Here are some of the advantages of using this method:

  • Modification of the program without extensive rewriting
  • Integration with a Human Machine Interface (HMI) to control, modify and/or troubleshoot
  • Ability to sequence forward and backward
  • Easily understood the logic to follow. Looking at the pointers can the on compare instruction will quickly tell you what sensor is not being made.
Troubleshooting this method of programming is easily done. Compare the bits in the input pointed word to the actual bits form the input in binary format. The difference is the input/output that is not working.
The program is basically broken down into three sections:
  • Inputs – Setting bits in the input channel based upon actual and internal conditions.
  • Control  – Control of the pointers, mask and setting the output channel.
  • Outputs – Using the output channel to activate the actual and internal actions required.
 Inputs – Building a PLC Program  – Traffic Light

The program is all controlled by one on-delay timer. This sets the minimum time between each step.
Building a PLC Program Part 4 - Traffic Light Building a PLC Program Part 4 - Traffic Light Building a PLC Program Part 4 - Traffic Light

Control – Building a PLC Program  – Traffic Light

This section of the control will tell the PLC what to do when the unit is first powered on. It resets the pointers and moves the initial output setting to the output word. You will see that since we have three different sequences running, there are three different reset rungs in parallel. The table input pointer is compared to the last value +1 of the sequence running.Building a PLC Program Part 4 - Traffic Light

The mask calculation is next. This is used to ignore the inputs that we do not want to see or may not know the status during the execution of the program.  Building a PLC Program Part 4 - Traffic Light

You will notice that the first three sequences are all the same. On this step, we then determine if the pointers need to be changed for the other two. The first is for weekday off-peak times.  Building a PLC Program Part 4 - Traffic Light

This is for the weekday peak times.  Building a PLC Program Part 4 - Traffic Light

We now compare the actual inputs after the mask with the input table word. If they are equal then move the output table word to the output channel and increment the pointers to the next step.  Building a PLC Program Part 4 - Traffic Light

Outputs – Building a PLC Program  – Traffic Light

The actual outputs are set using the output word bits. You will note that the flashing green lights are done when both green outputs are not on. This way will give me the greatest flexibility when developing different sequences. The ‘do not walk signal’ is not part of the sequence but is controlled when the flashing walk or walk is not on.

Building a PLC Program Part 4 - Traffic Light Building a PLC Program Part 4 - Traffic Light Building a PLC Program Part 4 - Traffic Light Building a PLC Program Part 4 - Traffic Light

The program will not change much for completely different sequences.

This program and the data tables can be downloaded here. Note that in order to run this program you must call up the input, mask, and output tables and write them to the simulator or PLC.

Part 5 will make a Game of Simon by learning all about bit manipulation and sequencers.

Watch on YouTube: Building a PLC Program that You can be Proud Of – Ultimate Traffic Light Control

If you have any questions or need further information please contact me.
Thank you,
Garry



If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLCs are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII, and Floating Point.

To get this free article, subscribe to my free email newsletter.


Use the information to inform other people how numbering systems work. Sign up now.

The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.


Here is a Method for a Faster PLC Program

PLC programming involves both direct and indirect addressing. Direct address programming involves writing each ladder logic rung to do the operation required. We often forget about using powerful indirect addressing to solve our logic.


Indirect Addressing – Faster PLC Program

The below-animated picture will show a simple example of using indirect addressing. This will use the MOVE instruction and transfer a word indirectly to output word V100. V[V0] means that the value in V0 will point to the V memory to get the value to move. You can think of this as a pointer for the memory location to move.

Here is a Method for a Faster PLC Program

Of course, we need to monitor V0. Our values are in sequence from V1 to V6. We need to ensure that V0 is always in the range from 1 to 6.

Program Example – Faster PLC Program

Let’s take a look at a program sample using the Do-more Designer Software. We will set up the sequence similar to the animation above but expand the program.
Just like above, we will set up the pointer at V0 and the output at V100 memory locations. V1 to V37 will hold our output data sequence. These are outputs that we want to set on each event and/or time frame. You can see some of the registers and the corresponding values. These are set as a hexadecimal value. The following link will provide a review of the numbering systems in the PLC. (WHAT EVERYBODY OUGHT TO KNOW ABOUT PLC (PROGRAMMABLE LOGIC CONTROLLER) NUMBERING SYSTEMS)

Here is a Method for a Faster PLC Program

This is the logic to set up the move instruction. The source is V[V0] which means the pointer is V0 in this memory area. The destination will be V100.

Here is a Method for a Faster PLC Program

An internal timing bit ST5($100ms) is used to increment the pointer V0. This could also be done by an event or series of events. The pointer is then compared to ensure that it is between 1 and 37.

Here is a Method for a Faster PLC Program

Finally, the output word is then transferred to the physical outputs. This is done by using MAPIO instruction. Each bit can be set independently.

Here is a Method for a Faster PLC Program

This example uses indirect addressing to program a sequence based upon time. We could just as easily used indirect addressing to compare inputs to a table and set the outputs accordingly. You can see how this method can greatly reduce the amount of time to develop your program. This holds especially true if the sequence needs to be changed. It would be just a matter of changing data values in the table.

The following are separate posts that use indirect addressing:

Building a PLC Program You Can Be Proud Of – Part 1
This uses the control of an intersection traffic light to demonstrate direct versus indirect addressing.

Building a PLC Program That You Can Be Proud Of – Part 2
A sample program to control valves. This uses indirect addressing for the inputs as well as the outputs.

Now You Can Have Robust Data Logging for Free – Part 1
Using indirect addressing, this sample program will log information in the PLC to be retrieved at a later time.

Indirect addressing is a powerful method of programming to simplify and program faster than you ever thought possible. You can even use indirect addressing in the PLC to scale a non-linear analog input signal. Let me know your thoughts on using indirect addressing. What can you come up with?

Watch on YouTube: Here is a Method That is Helping PLC Programmers to Program Faster

If you have any questions or need further information please contact me.
Thank you,
Garry



If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.

To get this free article, subscribe to my free email newsletter.


Use the information to inform other people how numbering systems work. Sign up now.

The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.


Now You Can Have Robust Data Logging for Free – Part 12

Now You Can Have Robust Data Logging for Free – Part 12

HTML and Scripting Languages

 We have the following accomplished:
  • PLC program
  • Visual Basic Program
  • Data collected in a Database
  • IIS web service established
  • ASP Script Written
iis106
Let’s take a closer look at the ASP Script ( AccRL.asp) that was written in part 11:



The <html> is at the start of the file and the </head> is at the end of the file. These tags all have to have a start and end.  The ‘/’ indicates the end of the tag.
The <head> is used to place the information for the web page. The refresh will load the page after 300 seconds (5 minutes). This way the information will always be the latest. The title is used to label the page. This is the information at the top of the browser. The SHORTCUT ICON is used for the icon at the top of the browser near the page address.
<html>

<head>
<meta HTTP-EQUIV=”Refresh” CONTENT=”300″>
<title>ACC Automation – Robust Logger</title>
<LINK REL=”SHORTCUT ICON” HREF=”http://192.168.1.3/ACC_Do.ico”/></head>

ActiveX Data Objects (ADO) is used to access databases from your web pages. ADOVBS.inc is a file that has all of the ADO constants defined.  Be sure to add this file in your root web application directory.
<!– #include virtual=”/adovbs.inc” –>

The <% and %> symbols indicate the start and finish of VBScript in the page. We dimension our variables for StartTime and EndTime. These will be used to determine how long our script took to execute.
<%
Dim StartTime, EndTime
StartTime = Timer

We dimension the variables that are used for the connection to the database file.
Dim OBJdbConnection
Dim rs1
Dim objCmd

We set up the connection to the database and determine what information we need to retrieve.
Set OBJdbConnection = Server.CreateObject(“ADODB.Connection”)

OBJdbConnection.Open “Provider=Microsoft.ACE.OLEDB.12.0;DATA SOURCE=C:\AccRL\data\AccRL.accdb;Persist Security Info=False;”
set rs1 = Server.CreateObject(“ADODB.recordset”)
with rs1
 .CursorType = adOpenForwardOnly
 .LockType = adLockReadOnly
 .CursorLocation = adUseServer
 .ActiveConnection = OBJdbConnection
 .Source = “SELECT * FROM Minute_Log;”
end with

Using getrows will allow us to execute the Select command and retrieve all of the information in one pass from the database.  This is the quickest method to get the information out quickly.
rs1.Open

arraytime = rs1.getrows()
rs1.close

We now write the information from the database to the page.
Response.Write arraytime(0,0) & “<br>”
Response.Write arraytime(1,0) & “<br>”
Response.Write Year(arraytime(1,0))& “/” & Right(“0” & Month(arraytime(1,0)), 2) & “/” & Right(“0” & Day(arraytime(1,0)), 2) & “<br>”
Response.Write arraytime(2,0)& “<br>”
Response.Write arraytime(3,0)& “<br>”
Response.Write arraytime(4,0)& “<br>”

The EndTime is now set and the total time it took for the process is displayed.
EndTime = Timer

Response.write “<p>Processing took “&(EndTime-StartTime)&” seconds<p>&nbsp;”
%>
</body>
</html>

Now that you have information into the database and IIS running, you can display the data in various ways.
Charts:
iis109 display
Graphs:
iis108 display Gauges:
iis107 display
This ends our robust logger design. For the complete PLC program, VB source code and web page file please send me an email and ask for the ACC Robust Logger Program. I will be happy to email you the information.
If you have any questions or need further information, please contact me.
Regards,
Garry

Now You Can Have Robust Data Logging for Free – Part 1
Now You Can Have Robust Data Logging for Free – Part 2
Now You Can Have Robust Data Logging for Free – Part 3
Now You Can Have Robust Data Logging for Free – Part 4
Now You Can Have Robust Data Logging for Free – Part 5
Now You Can Have Robust Data Logging for Free – Part 6
Now You Can Have Robust Data Logging for Free – Part 7
Now You Can Have Robust Data Logging for Free – Part 8
Now You Can Have Robust Data Logging for Free – Part 9
Now You Can Have Robust Data Logging for Free – Part 10
Now You Can Have Robust Data Logging for Free – Part 11
Now You Can Have Robust Data Logging for Free – Part 12




If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.

To get this free article, subscribe to my free email newsletter.


Use the information to inform other people how numbering systems work. Sign up now.

The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.


Now You Can Have Robust Data Logging for Free – Part 11

Now You Can Have Robust Data Logging for Free – Part 11

HTML and Scripting Languages

 We have the following accomplished:
  • PLC program
  • Visual Basic Program
  • Data collected in a Database
  • IIS web service established



The machine that has the IIS web service must have the Microsoft Access Database Engine 2010 installed. This can be obtained by the following link:
You can select the 32 bit or 64-bit version that matches your computer.

Microsoft Access Database Engine 2010 Redistributable
Note:  If you have office installed on your machine already then you probably will already have this file.

ActiveX Data Objects (ADO) is used to access databases from your web pages. ADOVBS.inc is a file that has all of the ADO constants defined.  Be sure to add this file in your root web application directory. How to add this code to a web page is shown in the sample code below.
You can download ADOVBS.inc from this site in text format. (Just rename to ADOVBS.inc from ADOVBS.txt)
ADO Introduction:
http://www.w3schools.com/asp/ado_intro.asp

Lets set up ASP on IIS to display any error messages to our browser.
Call up Control Panel and then go to Administrative Tools. Call up Internet Information Services (IIS) Manager.iis100

From IIS Manager, double click on ASP under IIS. Expand Debugging Properties and change the Send Errors To Browser to True.

iis102

iis103

Let’s also ensure that your browser is set to display the error messages in internet explorer (IE). Call up Internet options from the main settings.

iis104

iis105

Click the setting for ‘Show friendly HTTP error messages’. This will ensure that the error messages show up in your browser.

The last part of our project is to display the database information to the network. We do this by using a webpage. The HTML and VBScript can be writing in any editor. (Like Notepad)

There are also a great number of online editors that you can visually see what your page will look like while developing your code.
To learn more about VBScript following the link below:
Lets take a look at the AccRL.asp file:


<html>
<head>
<meta HTTP-EQUIV=”Refresh” CONTENT=”300″>
<title>ACC Automation – Robust Logger</title>
<LINK REL=”SHORTCUT ICON” HREF=”http://192.168.1.3/ACC_Do.ico”/></head>
<!– #include virtual=”/adovbs.inc” –>
<%
Dim StartTime, EndTime
StartTime = Timer

Dim OBJdbConnection
Dim rs1
Dim objCmd

Set OBJdbConnection = Server.CreateObject(“ADODB.Connection”)
OBJdbConnection.Open “Provider=Microsoft.ACE.OLEDB.12.0;DATA SOURCE=C:\AccRL\data\AccRL.accdb;Persist Security Info=False;”
set rs1 = Server.CreateObject(“ADODB.recordset”)
with rs1
 .CursorType = adOpenForwardOnly
 .LockType = adLockReadOnly
 .CursorLocation = adUseServer
 .ActiveConnection = OBJdbConnection
 .Source = “SELECT * FROM Minute_Log;”
end with

rs1.Open
arraytime = rs1.getrows()
rs1.close

Response.Write arraytime(0,0) & “<br>”
Response.Write arraytime(1,0) & “<br>”
Response.Write Year(arraytime(1,0))& “/” & Right(“0” & Month(arraytime(1,0)), 2) & “/” & Right(“0” & Day(arraytime(1,0)), 2) & “<br>”
Response.Write arraytime(2,0)& “<br>”
Response.Write arraytime(3,0)& “<br>”
Response.Write arraytime(4,0)& “<br>”

EndTime = Timer
Response.write “<p>Processing took “&(EndTime-StartTime)&” seconds<p>&nbsp;”
%>
</body>
</html>

Place this AccRL.asp file into the root directory of our web server. Call up the page though our browser (http:\\localhost\AccRL.asp) and the following output will be seen.
iis106
In part 12 we will break down the ASP code and modify. For the complete PLC program, VB source code and web page file please send me an email and ask for the ACC Robust Logger Program. I will be happy to email you the information.
If you have any questions or need further information, please contact me.
Regards,
Garry

Now You Can Have Robust Data Logging for Free – Part 1
Now You Can Have Robust Data Logging for Free – Part 2
Now You Can Have Robust Data Logging for Free – Part 3
Now You Can Have Robust Data Logging for Free – Part 4
Now You Can Have Robust Data Logging for Free – Part 5
Now You Can Have Robust Data Logging for Free – Part 6
Now You Can Have Robust Data Logging for Free – Part 7
Now You Can Have Robust Data Logging for Free – Part 8
Now You Can Have Robust Data Logging for Free – Part 9
Now You Can Have Robust Data Logging for Free – Part 10
Now You Can Have Robust Data Logging for Free – Part 11




If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.

To get this free article, subscribe to my free email newsletter.


Use the information to inform other people how numbering systems work. Sign up now.

The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.


Now You Can Have Robust Data Logging for Free – Part 10

Now You Can Have Robust Data Logging for Free – Part 10

Computer Web Server (IIS)

 We have come a long way. The PLC program has been written. The visual basic program has been written. Information is now being collected from the Do-more PLC via Modbus TCP and stored in a database using visual basic.
The next step is to deliver the information on the network. We will do this by installing Internet Information Services. (IIS) This is a group of internet servers that include a Web or Hypertext Transfer Protocol server (HTTP) and a File Transfer Protocol server (FTP). IIS will allow us to connect the physical hardware to the data. This could be desktop computers, laptops, tablets, cell phones, watches, etc. The advantage of using HTTP is that we can share the information with all of these devices without having to be concerned over the operating system of each of them. As long as they can display a web page we are good to go.



Active Service Pages (ASP) will be installed at the same time. This is a program that will run scripts at the server before delivering the HTML code to the browser. It is similar to CGI and Perl but is simpler and faster.
ASP.Net Tutorial
We will install this on a Windows 8.1 machine.
Call up the Control Panel.
  • Swiping in from the right and searching for “control panel”.
  • Win + x will call a menu to select the control panel.
IIS_000
Select Programs and Features
IIS_001
Select Turn Windows features on or off
IIS_002
Select ASP after expanding Internet Information Services / World Wide Web Services / Application Development Features. This will select all of the other options.
IIS_003
Hit OK to install the services.
IIS_004
IIS_005
We now have IIS installed.
IIS_006
Under the following default directory, you will find the location to put your web pages.
C:\inetpub\wwwroot\
IIS_007
If you call up the iisstart.htm file in this directory it will call up a page from Microsoft to explain the IIS web service.
IIS_009
Installing IIS on windows 7 and XP is very similar to the above procedure. Windows 98 you had to install a personal web service (PWS) and then ASP separately.
Further information on ASP can be obtained from the following website:
This site will walk you through ASP.
In part 11 we will look at HTML and scripting languages like JavaScript or VBScript.
If you have any questions or need further information, please contact me.
Regards,
Garry

Now You Can Have Robust Data Logging for Free – Part 1
Now You Can Have Robust Data Logging for Free – Part 2
Now You Can Have Robust Data Logging for Free – Part 3
Now You Can Have Robust Data Logging for Free – Part 4
Now You Can Have Robust Data Logging for Free – Part 5
Now You Can Have Robust Data Logging for Free – Part 6
Now You Can Have Robust Data Logging for Free – Part 7
Now You Can Have Robust Data Logging for Free – Part 8
Now You Can Have Robust Data Logging for Free – Part 9
Now You Can Have Robust Data Logging for Free – Part 10




If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.

To get this free article, subscribe to my free email newsletter.


Use the information to inform other people how numbering systems work. Sign up now.

The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.