There was also a real time clock chip that only required a free rom socket, to set the time you treated some of the address bits as data. On 10/07/2019 17:09, André Fachat wrote: > > > Am 10. Juli 2019 17:51:00 schrieb laughton_at_cyg.net >> >> >> Interesting... So, you'd read several bytes whose value you actually >> don't care about... but the decoder hardware would recognize *which* >> bytes you'd read; and, from that, infer what MMU operation you wanted? > > Yeah. I used this technique to implement IO ports on the Atari ST ROM > port :-) > > Just used a 256 byte address range and used the lower 8 address bits as > output value when an address in that block was read > > This way my Atari ST became an IEEE488 connected harddisk for my C64 :-) > > André > >> >> >> cheers >> J >> >> >>> and think about very unlikely >>> read sequences that won't be triggered by random register accesses. >>> Of course, with this method, such a register can't be read by the cpu. >>> >>> >>> >>> >>> Frank > > > >Received on 2020-05-29 22:30:05
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