"will the assembler will support..."

To answer questions like that, you should refer to the Manual for your assembler, and the Manual for the processor's Instruction Set.

The Manual for the 8051 Instruction Set can be found on the page on this site.

"what does it mean to think in negative logic"

Positive logic means '1' = 'True' = 'High' = 'On' etc;
Negative logic means '0' = 'True' = 'High' = 'On' etc.
The two are related by De Morgan's laws - see any standard logic textbook.