6502.org

Hello

I have been wondering, what hidden registers does 6502 have if any?
By hidden registers i mean registers that are not available to the programmer at all, cant be directly modified or read by any instructions and are only used for internal CPU operations.
For example in a hypothetical CPU a hidden register would be a swap register used only to temporary hold register values when swapping between registers.

Not really. The diagram at the end of the Hanson paper shows all the registers and latches in the chip

https://projects.ncsu.edu/wcae//WCAE1/hanson.pdf

The 6502 sometimes uses ALU is temporary storage area during some operations but there aren't any hidden registers as such. Its pretty minimal in its design.

One might consider the Instruction Register (IR) as being used only for internal operations. Unlike A X Y P and PC this register has no explicit instructions to modify it. But, as Bitwise said, it *is* noted in Hanson's diagram.

-- Jeff