how to use A5 for extened instructions

"I want to have similar extened instructions"

Then you will have to design your own processor, and design-in those instructions.

This forum is for Keil tools; not processor or instruction set design - so you really need to find a more appropriate forum.

Of course, once you've redesigned the instruction set, it will no longer be supported by the Keil tools - or, in fact, any standard 8051 tools.
So, again, you will have to find another forum to discuss tools & programming for your new processor.

"I want to have similar extened instructions"

Then you will have to design your own processor, and design-in those instructions.

This forum is for Keil tools; not processor or instruction set design - so you really need to find a more appropriate forum.

Of course, once you've redesigned the instruction set, it will no longer be supported by the Keil tools - or, in fact, any standard 8051 tools.
So, again, you will have to find another forum to discuss tools & programming for your new processor.

...it will no longer be supported by the Keil tools - or, in fact, any standard 8051 tools.

Yes it will - it's just that the extended instructions will not be used. Hopefully, the chip would be a strict super-set.

Yes, of course - thus rendering the whole operation pointless!

;-)