in the SiLabs forum someone showed SFR = -n
I have never used such and became curuous. I searched the Keil documentation but could nof find it.
Look in the header file - how is the SFR in question defined?
It will be a standard 'C' thing - not specitfic to Keil (other than, maybe, subject to the option to disable integer promotion)
As far as 'C' is concerned, it will follow the standard rules when assigning one type to another type
it is defined as SFR so my question still stands is it rerated as unsigned or signed
You need to be careful to flag it as a C51 question - there's nothing in the forum to tell that any more, and C51 questions are very rare.
I agree, the documentation omits this:
http://www.keil.com/support/man/docs/c51/c51_le_sfr.htm
But it wouldn't make sense to have SFRs signed - as that would imply sign extension, etc.