__SHADOW_RAM__

Greetings, All! Greetings, All. I decided to write this message here on for what reason: the other day Comrade called me. IVAN, and reported that in EMS when working with a disk or modem (Port #F3) Subj pops up (that’s understandable). Any person who has even the slightest idea about how our beloved SPECCY works, knows the port sampling conditions #FB: The Z80 should set its tires to address 11111011 IORQ -> 0 RD -> 0 armed with logic, Subj should respond to such a request, but there is one "BUT": _IN_PORT_DENCRYPTION_#FFFB_ACCEPT_ONLY_ONE_ADDRESS_BUS_ - A2, which is at zero and, accordingly, physical port _SHADOW_RAM_: XXXXXXXX XXXXX0XX ─ A standard request for port #F3, respectively: 11110011 ─ IORQ -> 0 WR or RD -> 0 (depending on which operation passes the processor over the port) The result of all this is obvious. Now it's time to say a few words about the scheme itself: 1) We take TTL logic chips (series 155, 555, 1533) 2) We connect the CS signal to the previous decoding circuit Subj, in that the point where the A2 signal was previously sent In general, I drew the diagram based on the principle:THE SIMPLER, THE MORE RELIABLE. WITH QUESTIONS AND SUGGESTIONS WRITE TO ME, AN. ════════════════════════════════ ════════════════════════════════ LA1 ┌─────┐ 1 │ & │ A0 ─────────┤ │ 2 │ │ A1 ─────────┤ │ 6 4 │ O──────┐ A3 ─────────┤ │ │ 5 │ │ │ LL1 LL1 A4 ─────────┤ │ │ ┌─────┐ ┌─────┐ │ │ │ 1 │ 1 │ 4 │ 1 │ └─────┘ └────┤ │ 3 ┌────┤ │ 6 │ 0────┘ │ O───O CS LA1 2 │ │ 5 │ │ ┌─────┐ ┌────┤ │ ┌────┤ │ 1 │ & │ │ │ │ │ │ │ A5 ─────────┤ │ │ └─────┘ │ └─────┘ 2 │ │ │ │ A6 ─────────┤ │ 6 │ │ 4 │ O──────┘ │ ┌────┤ │ │ ┌───* 5 │ │ │ ┌┴┐ └────┤ │ │ 10k │ │ │ │ │ └┬┘ └─────┘ │ │ │ O +5V │ A2 ──────────────────────────────────────┘═══════════════════════════════════════════════════════════════