IEEE 754 32bit floating point value.

[Jerson]

I have worked on the floating point library for the 8051. This is a converter I wrote in QuickBasic 4.5 to convert a floating number entered on the PC to floating point representation that can be understood by the micro controller. See if it will help you move ahead in your quest.

To the best of my recollection, the format is
8 bits biased exponent followed by 24 bits signed mantissa.

The idea is to move the mantissa till you get a 1 bit in the highest position of the mantissa and accordingly change the exponent by the amount you moved the mantissa. Then remove the highest bit (it is implicit) and put in the sign bit for the mantissa. A 1 bit here means it is a negative number.

That's all I can offer right now. I am a bit hazy on the details at the moment as it has been more than 10 years ago that I did this. If you need any help, let me know and I'll try to help.

DIM Mant AS SINGLE, Expo AS INTEGER
DIM bits AS INTEGER, Sign AS INTEGER

PRINT "CFLT converter for text to float51 format"
INPUT "Please enter the number : ", num

IF num < 0 THEN
  Sign = 1
  num = -num
END IF

Mant = num
Expo = &H80 + 24
FOR bits = 1 TO 24
  IF (Mant AND &H800000) THEN EXIT FOR
  Mant = Mant * 2
  Expo = Expo - 1
NEXT

'remove the MSB if +ve
IF Sign = 0 THEN
  Mant = Mant AND &H7FFFFF
END IF

PRINT "The floating point representation is  Exp, Mantissa"
PRINT HEX$(Expo); ", "; HEX$(Mant)

[cncmachineguy]

Adding to the confusion to try and shead some light. You say the number you get back could be 751, which would equal 75.1. how is this sent? is it :
00000001 01110111, or is it
00000111 01010001?

The first being stright binary and the second being packed BCD I will assume the first. Now when you say you need a 32 bit, floating point answer, seems to me there must be some format to this. for instance, does the device you are sending it to expect the decimal to be in any special place? is it good with a 5 place decimal or does it assume 2 place? how does the receiving end expect to see the number? I mean 32 bit for tempreture is a bit much I think, could be 32767.32767 to -32767.32767 degrees! or something like that. Either way I don't want to live there!!!

[Cobra_Phil]

I used this information to read floats from an AB plc and it worked fine. There is a subroutine for Int to Float.
http://melabs.com/resources/fp.htm

[shawn]

thanks for the replys everyone,
Ive been gone for a while and havent had time to suddy it all yet. Ill get back to it.
Thanks
Nick

[rsocor01]

thanks for the replys everyone,
Ive been gone for a while and havent had time to suddy it all yet. Ill get back to it.
Thanks
Nick

Shawn,

It looks like we were trying to reinvent the wheel. Everything that you need is provided in the melabs.com link that Cobra_Phil mentions above.

Robert