More TTL gates

A project log for PDPjr

Standalone DIY 16-bit computer "PDPii Junior"

SHAOSSHAOS 06/28/2019 at 05:193 Comments

Now it looks much closer to completion:

IC11 is bank register, that store 4 bits when LCDE=0, LCDRS=0 and STROB=1 for a short period of time and it's cleaned on boot (when BINIT=0). If LCDE=0 and LCDRS=1 then STROB goes out as OFLAG (will be used in future). Higher byte of the word is always going back to the BBQ-bus when !RDEN is 0 (Q-bus read cycle from address 0xF800...0xFFFE), but lower byte can be LCD data output if !RDEN=0, LCDE=1 and LCDRW=1 (read from LCD) or IEX0...IEX7 if !RDEN=0 and LCDE=0 (LCD disabled). Those 8 extra inputs are reserved for future so if it's not used then IC13 could be omited. REG0...REG7 are connected to LCD data bus only when LCDRW=0 (write to LCD).

Next I should add ROM 27C1024 and show how to mix RAM module and ROM address signals with some logic to get memory modes described earlier - TO BE CONTINUED


Kn/vD wrote 06/28/2019 at 06:42 point

Out of curiosity, what EDA is this?

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SHAOS wrote 06/28/2019 at 08:27 point

My own EDA :)

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Kn/vD wrote 06/28/2019 at 09:47 point

Nice! :)

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