Which standard is used by schneider to implement the 32 bit floating in modbus protocol? Has this procedure been recorded in document? As I need to use SUN ultra sparc to talk to Quantum PLC directly.

 

IEC 754

 

From the Modicon Ladder Logic Block Library (840USE10100) manual.

"...(Modicon) floating point functions require values in 32-bit IEEE floating point format. Each
value has two registers assigned to it - the eight most significant bits representing the
exponent and the other 23 bits (plus one assumed bit) representing the mantissa and the sign of
the value.
....
It is virtually impossible to recognize an FP representation on the programming panel..."

 

This standard comes from IEEE. Follow the link below for general description. Your floating point design in MODBUS driver should also account for word swapping and byte swapping.

"http://www.research.microsoft.com/~hollasch/cgindex/coding/ieeefloat.html":http://www.research.microsoft.com/~hollasch/cgindex/coding/ieeefloat.html

Regards,

Alexander Benim
Compressor Controls Corporation