If you could assign function to the *reserved A5 instruction in the 8051, what would it be? My vote: Choice 1, movx dptr,@dptr+a Choise 2, dec dptr *From what I recall, this instruction is reserved for the interrupt mechanism, which (upon an interrupt) crams this instruction into the decoder as a special jump-to-vector command. Thus, its likely we'll never see any variant actually using the A5 instruction, but its fun to wish just the same.
I think (some) debuggers already use this as their software breakpoint instruction?
Working from memory, I think that the op-code is reserved by Intel and has been used in the 251 to switch between the backward compatible 80C51 instruction set and the new super dooper but longer 251 instructions.
The A5 instruction is used as an ESCAPE prefix for the 251 mode instructions (from 8051 mode). It is also used as a prefix for other 8051 devices. In addition, some emulator vendors used it is a single-byte BREAK instruction. Jon
OKI has a 8051 (with a piggy back eprom), wich has a mov bit,bit instruction on A5
I've just checked the datasheet, and the Triscend E5 devices use the 0xA5 instruction as a Software Breakpoint