Re: Gemini 80-Bus System
From the 74LS221 data sheet function table read the row that is H L ^ this is the mode that is used. On a rising edge of input B (eg reset button pressed) the output Q goes high for the timing period and then low.
The timing period will be too short for you to observe with a meter - a logic probe with pulse detection of an 'scope or logic analyser is required. So this might actually be functioning despite so be careful.
This is then fed through the 74LS74 D type flip flop which synchronizes reset with M1. This keeps the reset short and means that it does not cause memory loss by interfering with the Z80 refresh cycles.
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