Well not really OT as I am going to use it in a PIC.

I've know all the years the different data types (integers) but had an
abrupt awakening yesterday that I don't know how it is represented in
byte form.
Anybody know where I can get more info?
Can anybody please tell me what -999 will be in 4 byte floating notation
(show me the 4 bytes), and how to calculate it?
This is for serial communications, my PIC must recognize the -999 as the
start of the packet.

Thanks
Quentin