[A83] Re: in/out


[Prev][Next][Index][Thread]

[A83] Re: in/out




> From: "Patai Gergely" <patai.ti@freemail.hu>
>
> I'm just reading this:
>
> When direct addressing is used (in a,(n); out (n),a) the
> address n is output on the lower 8 address lines, while the
> contents of a appear on the higher 8 address lines.
>
> Contrary to this, in the case of indirect addressing (in r,
> (c); out (c),r) the data in the register given appears on
> the data lines, while the contents of _BC_ are output on
> the address lines, i. e. 65536 ports can be addressed.
>
> Is that true?

B appears on the top half of the address bus as a side effect of the
internal structure. The IO device only gets selected with the lower part of
the address bus.

At least that's what the official docs say.




Follow-Ups: References: