🚀 go-pugleaf

In article <7576@ucdavis.ucdavis.edu> foss@iris.ucdavis.edu (Jim Alves-Foss) writes:
>In article <90226.104110TOMIII@MTUS5.BITNET> TOMIII@MTUS5.BITNET (Thomas Dwyer III) writes:
>>...
>>Ok people, how can the same port be both read-only and write-only?  Am
>>I missing something? 
>>...
>>Thanks,
>>Thomas Dwyer III                            TOMIII   @ MTUS5.BITNET
>>Network Programmer                          DWYERIII @ MTUS5.BITNET
>>Computing Technology Services
>>Michigan Technological University
>
>Well, In the PC architecture we have 512 (not 256) ports. 256 are Input ports
>and 256 are Output ports. Often a card will have a R/W register with a
>single address. In your case you have TWO DISTINCT registers, one input
>and one output but with the same address (064H(In) and 064H(Out)).
>
>Hope this helps.
>
>-Jim Alves-Foss (foss@iris.ucdavis.edu)  /* Of course these are MY opinions */
>                (foss@[127.120.57.20])   /* and may change without warning. */

I think you missed something here... the 80n806 supports 65535 ports, which
can be r/o, r/w, w/o depending on the hardware designer. An example is the
8250 UART in which the receiver nad transmitter are the same port. If you
write a value to the UART at 3F8H and the UART doesn't remove that byte you
can read that value again. I can't comment on the keyboard, since I have
never programmed the thing other than to make the lights dance on the AT
keyboard. Consider, though, that since the com1 UART lies at port addresses
3F8-3FF your statement about 512 ports is wrong.

Steve

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