Adding floats to a FIFO queue using FFL and FFU? (AB MicroLogix 1400)

Hello,

I'm currently programming a MicroLogix 1400 in RSLogix Micro, and I'm trying to put data into FIFO queues.

Would you know how to use the FFL and FFU instructions on float data types? RSLogix will not let me do this, as it gives an "invalid data type" error when I attempt to input a float data type into the "Source" entry of the FFL / FFU instructions.

If this is not possible in MicroLogix, is it possible in CompactLogix?

On a possibly related note, I am also confused why RSLogix will not let me view the binary representation of floats in the data table.

Thanks so much for your help.

For legacy systems (including any of the MicroLogix series) only the SLC platform allows floating-point entries into a FIFO "stack"; the rest of the Legacy CPUs allow only Hexadecimal, Binary or Integer constants (I believe ML1500 allows long-integer type constants.
Any of the Logix class controllers allow FIFO floating-point data entries.

About your second question...Since the radix (decimal)point of a floating point number "floats" (it could be placed anywhere relative to the significant digits of the number) its binary value cannot quite be represented at all times.
Currently, the IEEE 754 defines the representation of floating point data within the artificial intelligence systems.
http://en.wikipedia.org/wiki/Floating_point

Thanks for your reply dmargineau! You were really helpful!

Would you know how to use the FFL and FFU instructions on float data types?

Click to expand...

I can see a possible work-around. Use the regular old N7 Integers in your FIFO, but then )outside the FIFO, make each of the N7 words and index to a F8 Floating Point number. For example if your first FIFO stack storage location needs to be F8:1, then your FIFO would actualy use address N7:1, which should be set to a "1", and the Indirect Address to the stack would be F8:[N7:1] = F8:1