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About Opcodes in 8051 Instruction Set Manual

http://www.keil.com/support/man/docs/is51/is51_opcodes.htm lists 8051 instructions by HEX code. I had saw a line and make me confused. Why MOV direct, R8 appear in Hex Code 90 ?
I mean, in other hex code, only can operate R0~R7. ex: INC/DEC/ADD/ORL/...etc

R8 only can apply in operation MOV direct, R8 ?

And question 2 is: because R9~R15 are not list in this table, would R9~R15 not be operated in C166 system?