if the ALU added zeropage byte to X, does it mean that the hi byte of what is put into the adress bus is always 0?
Zero-page-indexed accesses will wrap within page zero. For instance, the following code will read memory[$0080] into register A:
Code:
ldx #$c0
lda $c0,x
lda $c0,x
a) im sorry i confused zeorpage with zeropage,x i mean the really question is if in zeropage the cpu puts always "0" to the HI part of the addr bus (HI 8 BITS) wich it is a retoric question i think cos if this werent in that way could not load from "zero page".
b) Regarding zeropage,x thats why i think the "wrap around" that there is in a code like: lda $f0,x, where x = $20. Just becouse the cpu cant work in 16 bit mode, in other words has an splited address bus of 8 bits.
But im answering to me.
Thanks anyway.
b) Regarding zeropage,x thats why i think the "wrap around" that there is in a code like: lda $f0,x, where x = $20. Just becouse the cpu cant work in 16 bit mode, in other words has an splited address bus of 8 bits.
But im answering to me.
Thanks anyway.
Yes. Pretty much by definition, if zero page is being accessed, the high 8 lines of the address bus will all be low. This is the case on the 2A03 and on the standard 6502. (I'm not sure if the external address bus is affected at all when accessing the I/O in zero page of special derivatives like the 6510).