Structured Text Programming

Good day to all,

I'm a proficient PLC Programmer in the Ladder format. Just recently I'm studying the Structured Text Programming and it's nature is really different. It's like I'm learning back to basics once again.

I already learned how to utilize the Conditional Statements (If, Else, Case, Of etc...) and also the Mathematical functions of ST. However, I'm still wondering how to use the "Timers, Counters, Shift Regs and Difu/Difd" in Structured Text.

Can anyone provide me a reference/manual on how to fully understand the Structured Text Programming? Any help will be appreciated. I'm by the way using Omron's CX-Programmer. Thank you very much,

Sincerely,
Andrei K.

Timer and Counter variables are not valid data types in OMRON's structured text programming.
You must create your own timer or counter using structured text statements. These both can use an incrementing method [a = a + 1] and comparison statement IF a = 60 THEN *********!

For a timer use one a structured text External Variables clock pulse bits to trigger your incrementer [ie P_1s will increment every second].

For DIFU/DIFD's and Shift Registers you will also have to construct your own version using ST.

In my experience Structured Text programming is best suited to complex math calculations and string manipulations.
Much easier to develop and understand than ladder.

For everything else I still prefer ladder.
Simpler for other using to comprehend, faster to develop and uses less PLC memory.
If you are intent on using ST then be sure to include clear and concise comments for other users.

Here are some examples of incrementing, DIFU and DIFD in structured text in a CP1L using CX Programmer V9.20.

Whoah, thank you there. I learned a lot from you. Another thing about "string manipulations" you have indicated. I want to learn a little bit about that. Can you give me an idea? Thanks so much.

Andreik, glad to help.

Attached is a very simple example of STRING usage within a Function block.
Note that STRING variables are NOT valid in CP series processors so the attached program is for a CJ1 series.

The program examines the string contained in DM100.
If one of three strings are matched then a unique bit is turned ON.

The first section 'LADDER METHOD' shows how to perform a string comparison in conventional ladder.
The Second section FUNCTION_BLOCK_METHOD performs the same comparison using a FB.
Note that a STRING variable can only be declared as an Internal Variable. To access external data it is necessary to use the AT(Specified Address) in the 'Advanced' setting of the internal variable. In the example the Internal Variable 'String_Data' has the AT set for D100.
Also note that DataType is STRING(10). In this case the program will evaluate a string up to 10 characters long contained in D100-D104.

This example demonstrates just how much easier it is to utilize structured text function blocks vs. conventional ladder when processing STRING data.

Hope this helps. Have fun!

CJ1M using CX Programmer V9.20

A Structured Text language referece can be found at page 156 of this appendix to another PLC series' user manual http://www.icpdas-usa.com/documents/User_Manual_I_8xx7_Appendix.pdf .

Oh yes, thank you. I've been wondering how to use these Strings especially with its application to HMI-to-PLC and vice versa. Now I understand how to use the ASCII codes. Thanks so much for the help.

Thank you TechEric, I've been compiling Structured Text Manuals to aid me on my studies and I already have manuals from different Brands. Yours will be helpful too. Thank you very much.

why invent when www.oscat.de has it all

Because not everyone speaks/reads German!
AND the examples show specific requirements of using structured text on an OMRON platform!

BITS N BYTES said:

Here are some examples of incrementing, DIFU and DIFD in structured text in a CP1L using CX Programmer V9.20.

Click to expand...

Thanks a lot Man!
Efficient and to the point!

I find the code rather confusing.

What is wrong with the following code (for a DIFU):

OUT := IN AND NOT IN_PREV;
IN_PREV := IN;

i GUESS the DIFU and DIFD need to created in ladder diagram and insert on symbols then use in ST.