plc5 fifo instruction help

[roy357]

hi every one,
I have a question about FIFO instruction, i need to to store data in just like the fifo does, but i need to do it with float point data type and in the plc5 instruction set manual tells me that i can use integer only as valid data type. is there a way to do it? the data i need to use are the form 1.33e-7. i use a plc5/20

thanks

roy:book:

 

[Ken Moore]

You can achieve similar results with a stack, and an index, maybe two indexes. You can also create a stack and "pop" the stack and move the data. If you could describe what your goal is, perhaps that will lead us to the best solution for your application.

 

[roy357]

the purpouse of doing this is to be able to see some data during the day maybe every hour, we go end look the last 60 results of a test there's nothing special but the problem is the data type that is float.

 

[roy357]

could you explain me how to do the indexing procedure that you mencioned im not plenty familiar with some expressions used in plc world

 

[Ken Moore]

Here's another way.
In this example F9:0 will hold the latest value, F9:1 the previous value, F9:2 next oldest etc.... all the way up to F9:59 which will hold the oldest value.
F10:0-F10:59 is just a holding register for the shift. The example shows your data coming from F8:0, adjust to fit your program.
When your data store bit is true, we copy the contents of F9 to F10, then copy the data back starting at F9:1, this in effect shifts the data values by one register, then we write the current value to F9:0
There is a more elegant way to do this, but this way is easier to follow.
Hope this gets you started.

 

[Ken Moore]

Forgot:
You will need a one shot after the trigger bit, to ensure you only shift once per event.

 

[roy357]

thanks a lot ken it really helped me.....thank you

 

[TConnolly]

You can avoid using a scratch file and reduce the number of memory copies if you can store the data upside down, That is, F9:0 is the oldest data and F9:60 is the newest data.

COP #F9:1 #F9:0 59
MOV F8:0 F9:59

In this example the COP instruction copies F9:1 down to F9:0, then F9:2 to F9:1, then F9:3 to F9:2, etc. Finally, the newest data is saved at F9:59.