HELP! why 253.14 with shift register?

[jeelin118]

hello people, im totally NEW in plc.
i'v read reference of ladder diagram (OMRON PLC CPM1A-20CDR).
why do people use 253.14 as data input of shift register?
i'v search around the internet for the usage of 253.14, but there aren't one!
i understand that 253.14 is normally open, but under which condition it will close and enable the shift register?
could someone please explain??

thanks A LOT!!

 

[sthompson]

hello people, im totally NEW in plc.
i'v read reference of ladder diagram (OMRON PLC).
why do people use 253.14 as data input of shift register?
i'v search around the internet for the usage of 253.14, but there aren't one!
i understand that 253.14 are normally open, but under which condition it will close and enable the shift register?
could someone please explain??

thanks A LOT!!

You are a little sketchy on details, but based on the Address, it looks like you are using a C200H Series PLC. If that is the case, then 253.14 is the Always Off Bit. So, I think you are going to give us a few more details on it's usage in your program. If you could post the Program File (Zip it first), we can have a look at how it is being used for you.

Also, post the exact model of Omron PLC you are using.

Stu......

 

[jeelin118]

hi,
im not sure about the model but i GUESS its CMP1A, because im a college student, we dont go that IN DEPTH about the plc model. we are not taught about the models, we learn only the basic programming language and were given task to write program for cylinder to work.

 

[sthompson]

hi,
im not sure about the model but i GUESS its CMP1A, because im a college student, we dont go that IN DEPTH about the plc model. we are not taught about the models, we learn only the basic programming language and were given task to write program for cylinder to work.

I don't do any programming with the CPM1A, however my CX-Programmer supports it. 253.14 is the Always Off Flag on it as well. Details and information are important if anyone is going to be able to help you. It is somewhat equivalent to "My car is Green, why won't it start?" You at least need to show us the PLC Code that is confusing you. As I said earlier, the entire program is best, since we can see everything in context. I see you have added some code to your original post. That is much more helpful, but is it everything that affects the Shift Register?

Stu....

 

[LadderLogic]

SFT(10) instruction is available for all the Omron PLC models. Below is the exact quote from the Instruction Reference Manual:​

When the execution condition on the shift input changes from OFF to ON, all
the data from St to E is shifted to the left by one bit (from the rightmost bit to
the leftmost bit), and the ON/OFF status of the data input is placed in the rightmost bit.​

So in your case, whenever "Clock" (200.02) bit goes off to on, all the bits in word HR00 are shifted and the available space is filled with a '0' bit - that is why there is 'Always off' (253.14) system bit at the 'Data' input. If someone wanted to fill the space with '1's, he would have to put 'Always on' instead.​

When 'Stop' (000.03) bit goes on, the shift register resets.​

 

[Ventax]

in your logic you move a value of 1 into HR00 in the second line
that gives you a word value of 0000 0001
by shifting a 0 into the register you effectively move the 1 over a bit each cycle
0000 0010
0000 0100

Etc

Have fun

 

[sthompson]

Right Click the SFT Instruction and then click on Instruction Help.

You can also go to the Omron Website at

http://www.omron247.com

Search for Document W353-E1-06. The SFT Instruction is on Page 422 Section 7-16.

There may also be a more suitable site near you that you can get manuals from.

Stu.....