How does PLC5 convert single floating point to two integers?

[wildswing]

Just curious. Does anyone know the specifics of how the PLC5 converts a single floating point to two integers and back using the COP command? Is it some standard formula?

From floating point to integer: SOR COP #F8:0 #N7:0 2 EOR
and from integer back to floating point: SOR COP #N7:0 #F8:1 1 EOR

 

[kamenges]

The copy instruction doesn't 'convert' anything, and that is really the power of the instruction. The COP command does a direct byte-for-byte transfer from the source to the destination. The float will be in IEEE format. Once you copy it to a pair of integers it is unintelligable when you look at the two integers as raw integers. You need to look at the whole 32-bit quantity as a float for it to make sense.

The real beauty of this comes in if you need to transport some floats in a block of integers or if you data transport mechanism only supports integer transfers. The copy will do a byte-for-byte copy of the float into two successive integers. you can transfer the data and re-assemble the float on the other side.

Keith

 

[TConnolly]

A single precision floating point number occupies 32 bits. Bits 0 to 22 are the mantissa of the number. Bits 23-30 are the exponent normalized to 128, and bit 31 is the sign bit. When you execute the command COP #F8:0 #N7:0 2 then the floating point sign is stored at N7:0/15, the exponent is at N7:0/7 thru N7:0/14 and the first seven bits of the mantissa are stored in N7:0/0 thru N7:0/6. The remaining 16 bits of the mantissa are in N7:1. It is an exact bit for bit copy from four bytes of memory in one location to 4 bytes of memory in another location.

Here is a tech note on how floating point numbers are stored in a PLC: http://domino.automation.rockwell.com/applications/kb/RAKB.nsf/0/85C2838CBFC456D285256AFB00695031?OpenDocument

Here is a handy web utility that lets you see exactly how a floating point number looks in binary: http://babbage.cs.qc.edu/courses/cs341/IEEE-754.html

 

[wildswing]

Thanks for the info fellas!